Add a helper to probe a DP link (read out the supported DPCD revision, maximum rate, link count and capabilities) as well as power up the DP link and configure it accordingly.
Reviewed-by: Alex Deucher alexander.deucher@amd.com Reviewed-by: Jani Nikula jani.nikula@intel.com Signed-off-by: Thierry Reding treding@nvidia.com --- Changes in v4: - fix a couple of typos in comments as pointed out by Alex Deucher
Changes in v3: - split into drm_dp_link_power_up() and drm_dp_link_configure() - do not change sink state for DPCD versions earlier than 1.1 - sleep for 1-2 ms after setting local sink to D0 state - read and write consecutive registers where possible - read DPCD revision when link is probed - remove duplicate kerneldoc
drivers/gpu/drm/drm_dp_helper.c | 94 +++++++++++++++++++++++++++++++++++++++++ include/drm/drm_dp_helper.h | 17 ++++++++ 2 files changed, 111 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index b26d46b00b05..eea15b1414ed 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -472,3 +472,97 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux, DP_LINK_STATUS_SIZE); } EXPORT_SYMBOL(drm_dp_dpcd_read_link_status); + +/** + * drm_dp_link_probe() - probe a DisplayPort link for capabilities + * @aux: DisplayPort AUX channel + * @link: pointer to structure in which to return link capabilities + * + * The structure filled in by this function can usually be passed directly + * into drm_dp_link_power_up() and drm_dp_link_configure() to power up and + * configure the link based on the link's capabilities. + * + * Returns 0 on success or a negative error code on failure. + */ +int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link) +{ + u8 values[3]; + int err; + + memset(link, 0, sizeof(*link)); + + err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values)); + if (err < 0) + return err; + + link->revision = values[0]; + link->rate = drm_dp_bw_code_to_link_rate(values[1]); + link->num_lanes = values[2] & DP_MAX_LANE_COUNT_MASK; + + if (values[2] & DP_ENHANCED_FRAME_CAP) + link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING; + + return 0; +} + +/** + * drm_dp_link_power_up() - power up a DisplayPort link + * @aux: DisplayPort AUX channel + * @link: pointer to a structure containing the link configuration + * + * Returns 0 on success or a negative error code on failure. + */ +int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link) +{ + u8 value; + int err; + + /* DP_SET_POWER register is only available on DPCD v1.1 and later */ + if (link->revision < 0x11) + return 0; + + err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value); + if (err < 0) + return err; + + value &= ~DP_SET_POWER_MASK; + value |= DP_SET_POWER_D0; + + err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value); + if (err < 0) + return err; + + /* + * According to the DP 1.1 specification, a "Sink Device must exit the + * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink + * Control Field" (register 0x600). + */ + usleep_range(1000, 2000); + + return 0; +} + +/** + * drm_dp_link_configure() - configure a DisplayPort link + * @aux: DisplayPort AUX channel + * @link: pointer to a structure containing the link configuration + * + * Returns 0 on success or a negative error code on failure. + */ +int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link) +{ + u8 values[2]; + int err; + + values[0] = drm_dp_link_rate_to_bw_code(link->rate); + values[1] = link->num_lanes; + + if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING) + values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN; + + err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values)); + if (err < 0) + return err; + + return 0; +} diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 8af695277a84..c7b3c736c40a 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -291,6 +291,7 @@ #define DP_SET_POWER 0x600 # define DP_SET_POWER_D0 0x1 # define DP_SET_POWER_D3 0x2 +# define DP_SET_POWER_MASK 0x3
#define DP_PSR_ERROR_STATUS 0x2006 /* XXX 1.2? */ # define DP_PSR_LINK_CRC_ERROR (1 << 0) @@ -468,4 +469,20 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux, int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux, u8 status[DP_LINK_STATUS_SIZE]);
+/* + * DisplayPort link + */ +#define DP_LINK_CAP_ENHANCED_FRAMING (1 << 0) + +struct drm_dp_link { + unsigned char revision; + unsigned int rate; + unsigned int num_lanes; + unsigned long capabilities; +}; + +int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link); +int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link); +int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link); + #endif /* _DRM_DP_HELPER_H_ */