Some DP dongles in particular seem to be fussy about too large link M/N values. Set specific value for N divider can resolve this issue per dongle vendor's comment. So configure N as constant value (0x8000) to instead of reduce M/N formula when specific DP dongle connected.
v2: add more comments for issue description and fix typo. v3: add lost commit messages back for version 2
Cc: Jani Nikula jani.nikula@intel.com Cc: Cooper Chiou cooper.chiou@intel.com Cc: Matt Atwood matthew.s.atwood@intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Dhinakaran Pandiyan dhinakaran.pandiyan@intel.com Cc: Clint Taylor clinton.a.taylor@intel.com Signed-off-by: Lee, Shawn C shawn.c.lee@intel.com --- drivers/gpu/drm/drm_dp_helper.c | 2 +- drivers/gpu/drm/i915/intel_display.c | 28 +++++++++++++--------------- drivers/gpu/drm/i915/intel_display.h | 2 +- drivers/gpu/drm/i915/intel_dp.c | 8 ++++---- drivers/gpu/drm/i915/intel_dp_mst.c | 6 +++--- include/drm/drm_dp_helper.h | 6 +++--- 6 files changed, 25 insertions(+), 27 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 0362c645d96e..f3a7563eb8a1 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -1269,7 +1269,7 @@ struct dpcd_quirk {
static const struct dpcd_quirk dpcd_quirk_list[] = { /* Analogix 7737 needs reduced M and N at HBR2 link rates */ - { OUI(0x00, 0x22, 0xb9), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_LIMITED_M_N) }, + { OUI(0x00, 0x22, 0xb9), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_CONSTANT_N) }, };
#undef OUI diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index ec3e24f07486..da0c7fbef3ef 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -6680,22 +6680,20 @@ intel_reduce_m_n_ratio(uint32_t *num, uint32_t *den)
static void compute_m_n(unsigned int m, unsigned int n, uint32_t *ret_m, uint32_t *ret_n, - bool reduce_m_n) + bool constant_n) { /* - * Reduce M/N as much as possible without loss in precision. Several DP - * dongles in particular seem to be fussy about too large *link* M/N - * values. The passed in values are more likely to have the least - * significant bits zero than M after rounding below, so do this first. + * Several DP dongles in particular seem to be fussy about + * too large link M/N values. Give N value as 0x8000 that + * should be acceptable by specific devices. 0x8000 is the + * specified fixed N value for asynchronous clock mode, + * which the devices expect also in synchronous clock mode. */ - if (reduce_m_n) { - while ((m & 1) == 0 && (n & 1) == 0) { - m >>= 1; - n >>= 1; - } - } + if (constant_n) + *ret_n = 0x8000; + else + *ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
- *ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX); *ret_m = div_u64((uint64_t) m * *ret_n, n); intel_reduce_m_n_ratio(ret_m, ret_n); } @@ -6704,18 +6702,18 @@ void intel_link_compute_m_n(int bits_per_pixel, int nlanes, int pixel_clock, int link_clock, struct intel_link_m_n *m_n, - bool reduce_m_n) + bool constant_n) { m_n->tu = 64;
compute_m_n(bits_per_pixel * pixel_clock, link_clock * nlanes * 8, &m_n->gmch_m, &m_n->gmch_n, - reduce_m_n); + constant_n);
compute_m_n(pixel_clock, link_clock, &m_n->link_m, &m_n->link_n, - reduce_m_n); + constant_n); }
static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv) diff --git a/drivers/gpu/drm/i915/intel_display.h b/drivers/gpu/drm/i915/intel_display.h index 43f080c6538d..8e8bd5eed2c2 100644 --- a/drivers/gpu/drm/i915/intel_display.h +++ b/drivers/gpu/drm/i915/intel_display.h @@ -379,7 +379,7 @@ struct intel_link_m_n { void intel_link_compute_m_n(int bpp, int nlanes, int pixel_clock, int link_clock, struct intel_link_m_n *m_n, - bool reduce_m_n); + bool constant_n);
bool is_ccs_modifier(u64 modifier); #endif diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c index 436c22de33b6..6b4c19123f2a 100644 --- a/drivers/gpu/drm/i915/intel_dp.c +++ b/drivers/gpu/drm/i915/intel_dp.c @@ -1998,8 +1998,8 @@ intel_dp_compute_config(struct intel_encoder *encoder, struct intel_connector *intel_connector = intel_dp->attached_connector; struct intel_digital_connector_state *intel_conn_state = to_intel_digital_connector_state(conn_state); - bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc, - DP_DPCD_QUIRK_LIMITED_M_N); + bool constant_n = drm_dp_has_quirk(&intel_dp->desc, + DP_DPCD_QUIRK_CONSTANT_N);
if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv) && port != PORT_A) pipe_config->has_pch_encoder = true; @@ -2064,7 +2064,7 @@ intel_dp_compute_config(struct intel_encoder *encoder, adjusted_mode->crtc_clock, pipe_config->port_clock, &pipe_config->dp_m_n, - reduce_m_n); + constant_n);
if (intel_connector->panel.downclock_mode != NULL && dev_priv->drrs.type == SEAMLESS_DRRS_SUPPORT) { @@ -2074,7 +2074,7 @@ intel_dp_compute_config(struct intel_encoder *encoder, intel_connector->panel.downclock_mode->clock, pipe_config->port_clock, &pipe_config->dp_m2_n2, - reduce_m_n); + constant_n); }
if (!HAS_DDI(dev_priv)) diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c index 352e5216cc65..184023435b08 100644 --- a/drivers/gpu/drm/i915/intel_dp_mst.c +++ b/drivers/gpu/drm/i915/intel_dp_mst.c @@ -45,8 +45,8 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder, int lane_count, slots; const struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode; int mst_pbn; - bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc, - DP_DPCD_QUIRK_LIMITED_M_N); + bool constant_n = drm_dp_has_quirk(&intel_dp->desc, + DP_DPCD_QUIRK_CONSTANT_N);
if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN) return false; @@ -87,7 +87,7 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder, adjusted_mode->crtc_clock, pipe_config->port_clock, &pipe_config->dp_m_n, - reduce_m_n); + constant_n);
pipe_config->dp_m_n.tu = slots;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 05cc31b5db16..f59359e42428 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -1260,12 +1260,12 @@ int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc, */ enum drm_dp_quirk { /** - * @DP_DPCD_QUIRK_LIMITED_M_N: + * @DP_DPCD_QUIRK_CONSTANT_N: * * The device requires main link attributes Mvid and Nvid to be limited - * to 16 bits. + * to 16 bits. So will give a constant value (0x8000) for compatability. */ - DP_DPCD_QUIRK_LIMITED_M_N, + DP_DPCD_QUIRK_CONSTANT_N, };
/**