At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted DPCD register values when reading from the 0xF0000- LTTPR range with an AUX transaction block size bigger than 1. The DP standard requires 0 to be returned - as for any other reserved/invalid addresses - but these monitors return the DPCD_REV register value repeated in each byte of the read buffer. This will in turn corrupt the values returned by the LTTPRs between the source and the monitor: LTTPRs must adjust the values they read from the downstream DPRX, for instance left-shift/init the downstream DP_PHY_REPEATER_CNT value. Since the value returned by the monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description: "LTTPR-related registers at DPCD Addresses F0000h through F02FFh are valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4 refers to the DPCD_REV or to the LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed at the VESA site to clarify this haven't been addressed), one possibility is that it's a restriction due to non-compliant monitors described above. Disabling the non-transparent LTTPR mode for all such monitors is not a viable solution: the transparent LTTPR mode has its own issue causing link training failures and this would affect a lot of monitors in use with DPCD_REV < 1.4. Instead this patch works around the problem by reading the LTTPR common and PHY cap registers one-by-one for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR common capabilities are read, so re-read the DPCD capabilities after the LTTPR common and PHY caps were read out.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531 Signed-off-by: Imre Deak imre.deak@intel.com --- drivers/gpu/drm/dp/drm_dp.c | 58 ++++++++++++------- .../drm/i915/display/intel_dp_link_training.c | 30 +++++++--- include/drm/dp/drm_dp_helper.h | 2 + 3 files changed, 59 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c index 703972ae14c64..f3950d42980f9 100644 --- a/drivers/gpu/drm/dp/drm_dp.c +++ b/drivers/gpu/drm/dp/drm_dp.c @@ -2390,9 +2390,36 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S } EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address, + u8 *buf, int buf_size) +{ + /* + * Some monitors with a DPCD_REV < 0x14 return corrupted values when + * reading from the 0xF0000- range with a block size bigger than 1. + */ + int block_size = dpcd[DP_DPCD_REV] < 0x14 ? 1 : buf_size; + int offset = 0; + int ret; + + while (offset < buf_size) { + ret = drm_dp_dpcd_read(aux, + address + offset, + &buf[offset], block_size); + if (ret < 0) + return ret; + + WARN_ON(ret != block_size); + + offset += block_size; + } + + return 0; +} + /** * drm_dp_read_lttpr_common_caps - read the LTTPR common capabilities * @aux: DisplayPort AUX channel + * @dpcd: DisplayPort configuration data * @caps: buffer to return the capability info in * * Read capabilities common to all LTTPRs. @@ -2400,25 +2427,19 @@ EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs); * Returns 0 on success or a negative error code on failure. */ int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], u8 caps[DP_LTTPR_COMMON_CAP_SIZE]) { - int ret; - - ret = drm_dp_dpcd_read(aux, - DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV, - caps, DP_LTTPR_COMMON_CAP_SIZE); - if (ret < 0) - return ret; - - WARN_ON(ret != DP_LTTPR_COMMON_CAP_SIZE); - - return 0; + return drm_dp_read_lttpr_regs(aux, dpcd, + DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV, + caps, DP_LTTPR_COMMON_CAP_SIZE); } EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps);
/** * drm_dp_read_lttpr_phy_caps - read the capabilities for a given LTTPR PHY * @aux: DisplayPort AUX channel + * @dpcd: DisplayPort configuration data * @dp_phy: LTTPR PHY to read the capabilities for * @caps: buffer to return the capability info in * @@ -2427,20 +2448,13 @@ EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps); * Returns 0 on success or a negative error code on failure. */ int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy, u8 caps[DP_LTTPR_PHY_CAP_SIZE]) { - int ret; - - ret = drm_dp_dpcd_read(aux, - DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy), - caps, DP_LTTPR_PHY_CAP_SIZE); - if (ret < 0) - return ret; - - WARN_ON(ret != DP_LTTPR_PHY_CAP_SIZE); - - return 0; + return drm_dp_read_lttpr_regs(aux, dpcd, + DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy), + caps, DP_LTTPR_PHY_CAP_SIZE); } EXPORT_SYMBOL(drm_dp_read_lttpr_phy_caps);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c index 5d98773efd1b3..fbee20a76cf44 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c @@ -55,6 +55,7 @@ static u8 *intel_dp_lttpr_phy_caps(struct intel_dp *intel_dp, }
static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; @@ -63,7 +64,7 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));
- if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dp_phy, phy_caps) < 0) { + if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dpcd, dp_phy, phy_caps) < 0) { drm_dbg_kms(&dp_to_i915(intel_dp)->drm, "[ENCODER:%d:%s][%s] failed to read the PHY caps\n", encoder->base.base.id, encoder->base.name, phy_name); @@ -77,10 +78,11 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp, phy_caps); }
-static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp) +static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE]) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; struct drm_i915_private *i915 = to_i915(encoder->base.dev); + int ret;
if (intel_dp_is_edp(intel_dp)) return false; @@ -92,8 +94,9 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp) if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915)) return false;
- if (drm_dp_read_lttpr_common_caps(&intel_dp->aux, - intel_dp->lttpr_common_caps) < 0) + ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd, + intel_dp->lttpr_common_caps); + if (ret < 0) goto reset_caps;
drm_dbg_kms(&dp_to_i915(intel_dp)->drm, @@ -122,14 +125,14 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable) return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1; }
-static int intel_dp_init_lttpr(struct intel_dp *intel_dp) +static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE]) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; struct drm_i915_private *i915 = to_i915(encoder->base.dev); int lttpr_count; int i;
- if (!intel_dp_read_lttpr_common_caps(intel_dp)) + if (!intel_dp_read_lttpr_common_caps(intel_dp, dpcd)) return 0;
lttpr_count = drm_dp_lttpr_count(intel_dp->lttpr_common_caps); @@ -168,7 +171,7 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp) }
for (i = 0; i < lttpr_count; i++) - intel_dp_read_lttpr_phy_caps(intel_dp, DP_PHY_LTTPR(i)); + intel_dp_read_lttpr_phy_caps(intel_dp, dpcd, DP_PHY_LTTPR(i));
return lttpr_count; } @@ -193,9 +196,18 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp) */ int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp) { - int lttpr_count = intel_dp_init_lttpr(intel_dp); + u8 dpcd[DP_RECEIVER_CAP_SIZE]; + int lttpr_count;
- /* The DPTX shall read the DPRX caps after LTTPR detection. */ + if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd)) + return -EIO; + + lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd); + + /* + * The DPTX shall read the DPRX caps after LTTPR detection, so re-read + * it here. + */ if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd)) { intel_dp_reset_lttpr_common_caps(intel_dp); return -EIO; diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h index 51e02cf75277e..1eccd97419436 100644 --- a/include/drm/dp/drm_dp_helper.h +++ b/include/drm/dp/drm_dp_helper.h @@ -2148,8 +2148,10 @@ bool drm_dp_read_sink_count_cap(struct drm_connector *connector, int drm_dp_read_sink_count(struct drm_dp_aux *aux);
int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], u8 caps[DP_LTTPR_COMMON_CAP_SIZE]); int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy, u8 caps[DP_LTTPR_PHY_CAP_SIZE]); int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]);
On Mon, Feb 28, 2022 at 10:12:34PM +0200, Imre Deak wrote:
At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted DPCD register values when reading from the 0xF0000- LTTPR range with an AUX transaction block size bigger than 1. The DP standard requires 0 to be returned - as for any other reserved/invalid addresses - but these monitors return the DPCD_REV register value repeated in each byte of the read buffer. This will in turn corrupt the values returned by the LTTPRs between the source and the monitor: LTTPRs must adjust the values they read from the downstream DPRX, for instance left-shift/init the downstream DP_PHY_REPEATER_CNT value. Since the value returned by the monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description: "LTTPR-related registers at DPCD Addresses F0000h through F02FFh are valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4 refers to the DPCD_REV or to the LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed at the VESA site to clarify this haven't been addressed), one possibility is that it's a restriction due to non-compliant monitors described above. Disabling the non-transparent LTTPR mode for all such monitors is not a viable solution: the transparent LTTPR mode has its own issue causing link training failures and this would affect a lot of monitors in use with DPCD_REV < 1.4. Instead this patch works around the problem by reading the LTTPR common and PHY cap registers one-by-one for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR common capabilities are read, so re-read the DPCD capabilities after the LTTPR common and PHY caps were read out.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531 Signed-off-by: Imre Deak imre.deak@intel.com
drivers/gpu/drm/dp/drm_dp.c | 58 ++++++++++++------- .../drm/i915/display/intel_dp_link_training.c | 30 +++++++--- include/drm/dp/drm_dp_helper.h | 2 + 3 files changed, 59 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c index 703972ae14c64..f3950d42980f9 100644 --- a/drivers/gpu/drm/dp/drm_dp.c +++ b/drivers/gpu/drm/dp/drm_dp.c @@ -2390,9 +2390,36 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S } EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address,
u8 *buf, int buf_size)+{
- /*
* Some monitors with a DPCD_REV < 0x14 return corrupted values when* reading from the 0xF0000- range with a block size bigger than 1.*/
This sounds really scary. Have we checked what other registers might end up corrupted? Eg. couple of rounds of comparing full dd bs=1 vs. dd bs=16.
- int block_size = dpcd[DP_DPCD_REV] < 0x14 ? 1 : buf_size;
- int offset = 0;
- int ret;
- while (offset < buf_size) {
Can we use a for loop?
ret = drm_dp_dpcd_read(aux,address + offset,&buf[offset], block_size);if (ret < 0)return ret;WARN_ON(ret != block_size);offset += block_size;- }
- return 0;
+}
On Tue, Mar 01, 2022 at 04:14:24PM +0200, Ville Syrjälä wrote:
On Mon, Feb 28, 2022 at 10:12:34PM +0200, Imre Deak wrote:
At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted DPCD register values when reading from the 0xF0000- LTTPR range with an AUX transaction block size bigger than 1. The DP standard requires 0 to be returned - as for any other reserved/invalid addresses - but these monitors return the DPCD_REV register value repeated in each byte of the read buffer. This will in turn corrupt the values returned by the LTTPRs between the source and the monitor: LTTPRs must adjust the values they read from the downstream DPRX, for instance left-shift/init the downstream DP_PHY_REPEATER_CNT value. Since the value returned by the monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description: "LTTPR-related registers at DPCD Addresses F0000h through F02FFh are valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4 refers to the DPCD_REV or to the LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed at the VESA site to clarify this haven't been addressed), one possibility is that it's a restriction due to non-compliant monitors described above. Disabling the non-transparent LTTPR mode for all such monitors is not a viable solution: the transparent LTTPR mode has its own issue causing link training failures and this would affect a lot of monitors in use with DPCD_REV < 1.4. Instead this patch works around the problem by reading the LTTPR common and PHY cap registers one-by-one for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR common capabilities are read, so re-read the DPCD capabilities after the LTTPR common and PHY caps were read out.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531 Signed-off-by: Imre Deak imre.deak@intel.com
drivers/gpu/drm/dp/drm_dp.c | 58 ++++++++++++------- .../drm/i915/display/intel_dp_link_training.c | 30 +++++++--- include/drm/dp/drm_dp_helper.h | 2 + 3 files changed, 59 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c index 703972ae14c64..f3950d42980f9 100644 --- a/drivers/gpu/drm/dp/drm_dp.c +++ b/drivers/gpu/drm/dp/drm_dp.c @@ -2390,9 +2390,36 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S } EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address,
u8 *buf, int buf_size)+{
- /*
* Some monitors with a DPCD_REV < 0x14 return corrupted values when* reading from the 0xF0000- range with a block size bigger than 1.*/This sounds really scary. Have we checked what other registers might end up corrupted? Eg. couple of rounds of comparing full dd bs=1 vs. dd bs=16.
Yes, checked now on a DELL P2715Q/ADLP/native-DP (w/o any LTTPR):
dd bs=1 count=1M failes at offset 81 and 83, bs=16 doesn't have this problem.
Replacing the above two bytes with 0s in the bs=1 output, the only difference is at 0xf0000:
bs=1: 0x12 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 bs=16: 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12 0x12
I attached the edid and bin files to the bugzilla ticket.
- int block_size = dpcd[DP_DPCD_REV] < 0x14 ? 1 : buf_size;
- int offset = 0;
- int ret;
- while (offset < buf_size) {
Can we use a for loop?
Yes, will change this.
ret = drm_dp_dpcd_read(aux,address + offset,&buf[offset], block_size);if (ret < 0)return ret;WARN_ON(ret != block_size);offset += block_size;- }
- return 0;
+}
-- Ville Syrjälä Intel
On Tue, Mar 01, 2022 at 08:14:25PM +0200, Imre Deak wrote:
On Tue, Mar 01, 2022 at 04:14:24PM +0200, Ville Syrjälä wrote:
On Mon, Feb 28, 2022 at 10:12:34PM +0200, Imre Deak wrote:
At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted DPCD register values when reading from the 0xF0000- LTTPR range with an AUX transaction block size bigger than 1. The DP standard requires 0 to be returned - as for any other reserved/invalid addresses - but these monitors return the DPCD_REV register value repeated in each byte of the read buffer. This will in turn corrupt the values returned by the LTTPRs between the source and the monitor: LTTPRs must adjust the values they read from the downstream DPRX, for instance left-shift/init the downstream DP_PHY_REPEATER_CNT value. Since the value returned by the monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description: "LTTPR-related registers at DPCD Addresses F0000h through F02FFh are valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4 refers to the DPCD_REV or to the LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed at the VESA site to clarify this haven't been addressed), one possibility is that it's a restriction due to non-compliant monitors described above. Disabling the non-transparent LTTPR mode for all such monitors is not a viable solution: the transparent LTTPR mode has its own issue causing link training failures and this would affect a lot of monitors in use with DPCD_REV < 1.4. Instead this patch works around the problem by reading the LTTPR common and PHY cap registers one-by-one for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR common capabilities are read, so re-read the DPCD capabilities after the LTTPR common and PHY caps were read out.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531 Signed-off-by: Imre Deak imre.deak@intel.com
drivers/gpu/drm/dp/drm_dp.c | 58 ++++++++++++------- .../drm/i915/display/intel_dp_link_training.c | 30 +++++++--- include/drm/dp/drm_dp_helper.h | 2 + 3 files changed, 59 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c index 703972ae14c64..f3950d42980f9 100644 --- a/drivers/gpu/drm/dp/drm_dp.c +++ b/drivers/gpu/drm/dp/drm_dp.c @@ -2390,9 +2390,36 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S } EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address,
u8 *buf, int buf_size)+{
- /*
* Some monitors with a DPCD_REV < 0x14 return corrupted values when* reading from the 0xF0000- range with a block size bigger than 1.*/This sounds really scary. Have we checked what other registers might end up corrupted? Eg. couple of rounds of comparing full dd bs=1 vs. dd bs=16.
Yes, checked now on a DELL P2715Q/ADLP/native-DP (w/o any LTTPR):
dd bs=1 count=1M failes at offset 81 and 83, bs=16 doesn't have this problem.
Huh. Oh well, it's a Dell monitor after all. Not sure what else I was expecting tbh.
At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted DPCD register values when reading from the 0xF0000- LTTPR range with an AUX transaction block size bigger than 1. The DP standard requires 0 to be returned - as for any other reserved/invalid addresses - but these monitors return the DPCD_REV register value repeated in each byte of the read buffer. This will in turn corrupt the values returned by the LTTPRs between the source and the monitor: LTTPRs must adjust the values they read from the downstream DPRX, for instance left-shift/init the downstream DP_PHY_REPEATER_CNT value. Since the value returned by the monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description: "LTTPR-related registers at DPCD Addresses F0000h through F02FFh are valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4 refers to the DPCD_REV or to the LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed at the VESA site to clarify this haven't been addressed), one possibility is that it's a restriction due to non-compliant monitors described above. Disabling the non-transparent LTTPR mode for all such monitors is not a viable solution: the transparent LTTPR mode has its own issue causing link training failures and this would affect a lot of monitors in use with DPCD_REV < 1.4. Instead this patch works around the problem by reading the LTTPR common and PHY cap registers one-by-one for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR common capabilities are read, so re-read the DPCD capabilities after the LTTPR common and PHY caps were read out.
v2: - Use for instead of a while loop. (Ville) - Add to code comment the monitor model with the problem.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531 Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: Imre Deak imre.deak@intel.com --- drivers/gpu/drm/dp/drm_dp.c | 57 ++++++++++++------- .../drm/i915/display/intel_dp_link_training.c | 30 +++++++--- include/drm/dp/drm_dp_helper.h | 2 + 3 files changed, 58 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c index 703972ae14c64..58744f83931af 100644 --- a/drivers/gpu/drm/dp/drm_dp.c +++ b/drivers/gpu/drm/dp/drm_dp.c @@ -2390,9 +2390,35 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S } EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address, + u8 *buf, int buf_size) +{ + /* + * At least the DELL P2715Q monitor with a DPCD_REV < 0x14 returns + * corrupted values when reading from the 0xF0000- range with a block + * size bigger than 1. + */ + int block_size = dpcd[DP_DPCD_REV] < 0x14 ? 1 : buf_size; + int offset; + int ret; + + for (offset = 0; offset < buf_size; offset += block_size) { + ret = drm_dp_dpcd_read(aux, + address + offset, + &buf[offset], block_size); + if (ret < 0) + return ret; + + WARN_ON(ret != block_size); + } + + return 0; +} + /** * drm_dp_read_lttpr_common_caps - read the LTTPR common capabilities * @aux: DisplayPort AUX channel + * @dpcd: DisplayPort configuration data * @caps: buffer to return the capability info in * * Read capabilities common to all LTTPRs. @@ -2400,25 +2426,19 @@ EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs); * Returns 0 on success or a negative error code on failure. */ int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], u8 caps[DP_LTTPR_COMMON_CAP_SIZE]) { - int ret; - - ret = drm_dp_dpcd_read(aux, - DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV, - caps, DP_LTTPR_COMMON_CAP_SIZE); - if (ret < 0) - return ret; - - WARN_ON(ret != DP_LTTPR_COMMON_CAP_SIZE); - - return 0; + return drm_dp_read_lttpr_regs(aux, dpcd, + DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV, + caps, DP_LTTPR_COMMON_CAP_SIZE); } EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps);
/** * drm_dp_read_lttpr_phy_caps - read the capabilities for a given LTTPR PHY * @aux: DisplayPort AUX channel + * @dpcd: DisplayPort configuration data * @dp_phy: LTTPR PHY to read the capabilities for * @caps: buffer to return the capability info in * @@ -2427,20 +2447,13 @@ EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps); * Returns 0 on success or a negative error code on failure. */ int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy, u8 caps[DP_LTTPR_PHY_CAP_SIZE]) { - int ret; - - ret = drm_dp_dpcd_read(aux, - DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy), - caps, DP_LTTPR_PHY_CAP_SIZE); - if (ret < 0) - return ret; - - WARN_ON(ret != DP_LTTPR_PHY_CAP_SIZE); - - return 0; + return drm_dp_read_lttpr_regs(aux, dpcd, + DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy), + caps, DP_LTTPR_PHY_CAP_SIZE); } EXPORT_SYMBOL(drm_dp_read_lttpr_phy_caps);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c index 5d98773efd1b3..fbee20a76cf44 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c @@ -55,6 +55,7 @@ static u8 *intel_dp_lttpr_phy_caps(struct intel_dp *intel_dp, }
static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; @@ -63,7 +64,7 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));
- if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dp_phy, phy_caps) < 0) { + if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dpcd, dp_phy, phy_caps) < 0) { drm_dbg_kms(&dp_to_i915(intel_dp)->drm, "[ENCODER:%d:%s][%s] failed to read the PHY caps\n", encoder->base.base.id, encoder->base.name, phy_name); @@ -77,10 +78,11 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp, phy_caps); }
-static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp) +static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE]) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; struct drm_i915_private *i915 = to_i915(encoder->base.dev); + int ret;
if (intel_dp_is_edp(intel_dp)) return false; @@ -92,8 +94,9 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp) if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915)) return false;
- if (drm_dp_read_lttpr_common_caps(&intel_dp->aux, - intel_dp->lttpr_common_caps) < 0) + ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd, + intel_dp->lttpr_common_caps); + if (ret < 0) goto reset_caps;
drm_dbg_kms(&dp_to_i915(intel_dp)->drm, @@ -122,14 +125,14 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable) return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1; }
-static int intel_dp_init_lttpr(struct intel_dp *intel_dp) +static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE]) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; struct drm_i915_private *i915 = to_i915(encoder->base.dev); int lttpr_count; int i;
- if (!intel_dp_read_lttpr_common_caps(intel_dp)) + if (!intel_dp_read_lttpr_common_caps(intel_dp, dpcd)) return 0;
lttpr_count = drm_dp_lttpr_count(intel_dp->lttpr_common_caps); @@ -168,7 +171,7 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp) }
for (i = 0; i < lttpr_count; i++) - intel_dp_read_lttpr_phy_caps(intel_dp, DP_PHY_LTTPR(i)); + intel_dp_read_lttpr_phy_caps(intel_dp, dpcd, DP_PHY_LTTPR(i));
return lttpr_count; } @@ -193,9 +196,18 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp) */ int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp) { - int lttpr_count = intel_dp_init_lttpr(intel_dp); + u8 dpcd[DP_RECEIVER_CAP_SIZE]; + int lttpr_count;
- /* The DPTX shall read the DPRX caps after LTTPR detection. */ + if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd)) + return -EIO; + + lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd); + + /* + * The DPTX shall read the DPRX caps after LTTPR detection, so re-read + * it here. + */ if (drm_dp_read_dpcd_caps(&intel_dp->aux, intel_dp->dpcd)) { intel_dp_reset_lttpr_common_caps(intel_dp); return -EIO; diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h index 51e02cf75277e..1eccd97419436 100644 --- a/include/drm/dp/drm_dp_helper.h +++ b/include/drm/dp/drm_dp_helper.h @@ -2148,8 +2148,10 @@ bool drm_dp_read_sink_count_cap(struct drm_connector *connector, int drm_dp_read_sink_count(struct drm_dp_aux *aux);
int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], u8 caps[DP_LTTPR_COMMON_CAP_SIZE]); int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux, + const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy, u8 caps[DP_LTTPR_PHY_CAP_SIZE]); int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]);
On Tue, Mar 22, 2022 at 04:38:44PM +0200, Imre Deak wrote:
At least some DELL monitors (P2715Q) with DPCD_REV 1.2 return corrupted DPCD register values when reading from the 0xF0000- LTTPR range with an AUX transaction block size bigger than 1. The DP standard requires 0 to be returned - as for any other reserved/invalid addresses - but these monitors return the DPCD_REV register value repeated in each byte of the read buffer. This will in turn corrupt the values returned by the LTTPRs between the source and the monitor: LTTPRs must adjust the values they read from the downstream DPRX, for instance left-shift/init the downstream DP_PHY_REPEATER_CNT value. Since the value returned by the monitor's DPRX is non-zero the adjusted values will be corrupt.
Reading the LTTPR registers one-by-one instead of reading all of them with a single AUX transfer works around the issue.
According to the DP standard's 0xF0000 register description: "LTTPR-related registers at DPCD Addresses F0000h through F02FFh are valid only for DPCD r1.4 (or higher)." While it's unclear if DPCD r1.4 refers to the DPCD_REV or to the LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV register (tickets filed at the VESA site to clarify this haven't been addressed), one possibility is that it's a restriction due to non-compliant monitors described above. Disabling the non-transparent LTTPR mode for all such monitors is not a viable solution: the transparent LTTPR mode has its own issue causing link training failures and this would affect a lot of monitors in use with DPCD_REV < 1.4. Instead this patch works around the problem by reading the LTTPR common and PHY cap registers one-by-one for any monitor with a DPCD_REV < 1.4.
The standard requires the DPCD capabilites to be read after the LTTPR common capabilities are read, so re-read the DPCD capabilities after the LTTPR common and PHY caps were read out.
v2:
- Use for instead of a while loop. (Ville)
- Add to code comment the monitor model with the problem.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4531 Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: Imre Deak imre.deak@intel.com
Reviewed-by: Ville Syrjälä ville.syrjala@linux.intel.com
drivers/gpu/drm/dp/drm_dp.c | 57 ++++++++++++------- .../drm/i915/display/intel_dp_link_training.c | 30 +++++++--- include/drm/dp/drm_dp_helper.h | 2 + 3 files changed, 58 insertions(+), 31 deletions(-)
diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c index 703972ae14c64..58744f83931af 100644 --- a/drivers/gpu/drm/dp/drm_dp.c +++ b/drivers/gpu/drm/dp/drm_dp.c @@ -2390,9 +2390,35 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S } EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
+static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address,
u8 *buf, int buf_size)+{
- /*
* At least the DELL P2715Q monitor with a DPCD_REV < 0x14 returns* corrupted values when reading from the 0xF0000- range with a block* size bigger than 1.*/- int block_size = dpcd[DP_DPCD_REV] < 0x14 ? 1 : buf_size;
- int offset;
- int ret;
- for (offset = 0; offset < buf_size; offset += block_size) {
ret = drm_dp_dpcd_read(aux,address + offset,&buf[offset], block_size);if (ret < 0)return ret;WARN_ON(ret != block_size);- }
- return 0;
+}
/**
- drm_dp_read_lttpr_common_caps - read the LTTPR common capabilities
- @aux: DisplayPort AUX channel
- @dpcd: DisplayPort configuration data
- @caps: buffer to return the capability info in
- Read capabilities common to all LTTPRs.
@@ -2400,25 +2426,19 @@ EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
- Returns 0 on success or a negative error code on failure.
*/ int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux,
const u8 dpcd[DP_RECEIVER_CAP_SIZE], u8 caps[DP_LTTPR_COMMON_CAP_SIZE]){
- int ret;
- ret = drm_dp_dpcd_read(aux,
DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV,caps, DP_LTTPR_COMMON_CAP_SIZE);- if (ret < 0)
return ret;- WARN_ON(ret != DP_LTTPR_COMMON_CAP_SIZE);
- return 0;
- return drm_dp_read_lttpr_regs(aux, dpcd,
DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV,caps, DP_LTTPR_COMMON_CAP_SIZE);} EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps);
/**
- drm_dp_read_lttpr_phy_caps - read the capabilities for a given LTTPR PHY
- @aux: DisplayPort AUX channel
- @dpcd: DisplayPort configuration data
- @dp_phy: LTTPR PHY to read the capabilities for
- @caps: buffer to return the capability info in
@@ -2427,20 +2447,13 @@ EXPORT_SYMBOL(drm_dp_read_lttpr_common_caps);
- Returns 0 on success or a negative error code on failure.
*/ int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux,
const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy, u8 caps[DP_LTTPR_PHY_CAP_SIZE]){
- int ret;
- ret = drm_dp_dpcd_read(aux,
DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy),caps, DP_LTTPR_PHY_CAP_SIZE);- if (ret < 0)
return ret;- WARN_ON(ret != DP_LTTPR_PHY_CAP_SIZE);
- return 0;
- return drm_dp_read_lttpr_regs(aux, dpcd,
DP_TRAINING_AUX_RD_INTERVAL_PHY_REPEATER(dp_phy),caps, DP_LTTPR_PHY_CAP_SIZE);} EXPORT_SYMBOL(drm_dp_read_lttpr_phy_caps);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c index 5d98773efd1b3..fbee20a76cf44 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c @@ -55,6 +55,7 @@ static u8 *intel_dp_lttpr_phy_caps(struct intel_dp *intel_dp, }
static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy){ struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; @@ -63,7 +64,7 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));
- if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dp_phy, phy_caps) < 0) {
- if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dpcd, dp_phy, phy_caps) < 0) { drm_dbg_kms(&dp_to_i915(intel_dp)->drm, "[ENCODER:%d:%s][%s] failed to read the PHY caps\n", encoder->base.base.id, encoder->base.name, phy_name);
@@ -77,10 +78,11 @@ static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp, phy_caps); }
-static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp) +static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE]) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; struct drm_i915_private *i915 = to_i915(encoder->base.dev);
int ret;
if (intel_dp_is_edp(intel_dp)) return false;
@@ -92,8 +94,9 @@ static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp) if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915)) return false;
- if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
intel_dp->lttpr_common_caps) < 0)
ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd,
intel_dp->lttpr_common_caps);if (ret < 0) goto reset_caps;
drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
@@ -122,14 +125,14 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable) return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1; }
-static int intel_dp_init_lttpr(struct intel_dp *intel_dp) +static int intel_dp_init_lttpr(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE]) { struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base; struct drm_i915_private *i915 = to_i915(encoder->base.dev); int lttpr_count; int i;
- if (!intel_dp_read_lttpr_common_caps(intel_dp))
if (!intel_dp_read_lttpr_common_caps(intel_dp, dpcd)) return 0;
lttpr_count = drm_dp_lttpr_count(intel_dp->lttpr_common_caps);
@@ -168,7 +171,7 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp) }
for (i = 0; i < lttpr_count; i++)
intel_dp_read_lttpr_phy_caps(intel_dp, DP_PHY_LTTPR(i));
intel_dp_read_lttpr_phy_caps(intel_dp, dpcd, DP_PHY_LTTPR(i));return lttpr_count;
} @@ -193,9 +196,18 @@ static int intel_dp_init_lttpr(struct intel_dp *intel_dp) */ int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp) {
- int lttpr_count = intel_dp_init_lttpr(intel_dp);
- u8 dpcd[DP_RECEIVER_CAP_SIZE];
- int lttpr_count;
- /* The DPTX shall read the DPRX caps after LTTPR detection. */
- if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd))
return -EIO;- lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd);
- /*
* The DPTX shall read the DPRX caps after LTTPR detection, so re-read* it here.*/diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h index 51e02cf75277e..1eccd97419436 100644 --- a/include/drm/dp/drm_dp_helper.h +++ b/include/drm/dp/drm_dp_helper.h @@ -2148,8 +2148,10 @@ bool drm_dp_read_sink_count_cap(struct drm_connector *connector, int drm_dp_read_sink_count(struct drm_dp_aux *aux);
int drm_dp_read_lttpr_common_caps(struct drm_dp_aux *aux,
const u8 dpcd[DP_RECEIVER_CAP_SIZE], u8 caps[DP_LTTPR_COMMON_CAP_SIZE]);int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux,
const u8 dpcd[DP_RECEIVER_CAP_SIZE], enum drm_dp_phy dp_phy, u8 caps[DP_LTTPR_PHY_CAP_SIZE]);int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]);
2.30.2
dri-devel@lists.freedesktop.org
-
Imre Deak -
Ville Syrjälä