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@xxxxxxxxxxxxxxx> > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > --- > 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]); > -- > 2.30.2 -- Ville Syrjälä Intel
