On Thu, Apr 14, 2022 at 01:49:54PM +0300, Jani Nikula wrote: > On Sat, 09 Apr 2022, Imre Deak <imre.d...@intel.com> wrote: > > Some ADLP DP link configuration at least with multiple LTTPRs expects > > the first DPCD access during the LTTPR/DPCD detection after hotplug to > > be a read from the LTTPR range starting with > > DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV. The side effect of > > this read is to put each LTTPR into the LTTPR transparent or LTTPR > > non-transparent mode. > > > > The lack of the above read may leave some of the LTTPRs in non-LTTPR > > mode, while other LTTPRs in LTTPR transparent or LTTPR non-transparent > > mode (for instance LTTPRs after system suspend/resume that kept their > > mode from before suspend). Due to the different AUX timeouts the > > different modes imply, the DPCD access from a non-LTTPR range will > > timeout and lead to an LTTPR generated hotplug towards the source (which > > the LTTPR firmware uses to account for buggy TypeC adapters with a long > > wake-up delay). > > > > To avoid the above AUX timeout and subsequent hotplug interrupt, make > > sure that the first DPCD access during detection is a read from an > > LTTPR register. > > > > VLK: SYSCROS-72939 > > > > v2: Keep DPCD read-out working on non-LTTPR platforms. > > > > Signed-off-by: Imre Deak <imre.d...@intel.com> > > I kinda dislike how complicated this looks for a diff so small. *shrug*. > Seems to do what it says on the box,
I can have a better summary of what the patch does and why at the beginning of the commit message. Imo the details for the related LTTPR behavior are still useful for later reference; it's not too intuitive with the read side-effects for instance, neither it is well documented by the DP standard. > Reviewed-by: Jani Nikula <jani.nik...@intel.com> Thanks. I pushed the dependent d8bb92e70a43 ("drm/dp: Factor out a function to probe a DPCD address") patch to drm-misc-next. Could you help back merging it to drm-intel-next? > > --- > > .../drm/i915/display/intel_dp_link_training.c | 33 ++++++++++--------- > > 1 file changed, 17 insertions(+), 16 deletions(-) > > > > 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 26f9e2b748e40..9feaf1a589f38 100644 > > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c > > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c > > @@ -82,19 +82,8 @@ 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; > > - > > - /* > > - * Detecting LTTPRs must be avoided on platforms with an AUX timeout > > - * period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1). > > - */ > > - if (DISPLAY_VER(i915) < 10 || IS_GEMINILAKE(i915)) > > - return false; > > - > > ret = drm_dp_read_lttpr_common_caps(&intel_dp->aux, dpcd, > > intel_dp->lttpr_common_caps); > > if (ret < 0) > > @@ -197,13 +186,25 @@ static int intel_dp_init_lttpr(struct intel_dp > > *intel_dp, const u8 dpcd[DP_RECEI > > */ > > int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp) > > { > > - u8 dpcd[DP_RECEIVER_CAP_SIZE]; > > - int lttpr_count; > > + struct drm_i915_private *i915 = dp_to_i915(intel_dp); > > + int lttpr_count = 0; > > > > - if (drm_dp_read_dpcd_caps(&intel_dp->aux, dpcd)) > > - return -EIO; > > + /* > > + * Detecting LTTPRs must be avoided on platforms with an AUX timeout > > + * period < 3.2ms. (see DP Standard v2.0, 2.11.2, 3.6.6.1). > > + */ > > + if (!intel_dp_is_edp(intel_dp) && > > + (DISPLAY_VER(i915) >= 10 && !IS_GEMINILAKE(i915))) { > > + u8 dpcd[DP_RECEIVER_CAP_SIZE]; > > > > - lttpr_count = intel_dp_init_lttpr(intel_dp, dpcd); > > + if (drm_dp_dpcd_probe(&intel_dp->aux, > > DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV)) > > + return -EIO; > > + > > + 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 > > -- > Jani Nikula, Intel Open Source Graphics Center