On Fri, Mar 19, 2021 at 01:25:08PM -0400, Lyude Paul wrote: > On Fri, 2021-03-19 at 01:17 +0200, Imre Deak wrote: > > On Fri, Mar 19, 2021 at 12:04:54AM +0200, Almahallawy, Khaled wrote: > > > On Thu, 2021-03-18 at 20:06 +0200, Imre Deak wrote: > > > > On Thu, Mar 18, 2021 at 07:49:13PM +0200, Imre Deak wrote: > > > > > On Thu, Mar 18, 2021 at 07:33:20PM +0200, Ville Syrjälä wrote: > > > > > > On Wed, Mar 17, 2021 at 08:48:59PM +0200, Imre Deak wrote: > > > > > > > The spec requires to use at least 3.2ms for the AUX timeout > > > > > > > period if > > > > > > > there are LT-tunable PHY Repeaters on the link (2.11.2). An > > > > > > > upcoming > > > > > > > spec update makes this more specific, by requiring a 3.2ms > > > > > > > minimum > > > > > > > timeout period for the LTTPR detection reading the 0xF0000- > > > > > > > 0xF0007 > > > > > > > range (3.6.5.1). > > > > > > > > > > > > I'm pondering if we could reduce the timeout after having > > > > > > determined > > > > > > wherther LTTPRs are present or not? But maybe that wouldn't > > > > > > really speed > > > > > > up anything since we can't reduce the timeout until after > > > > > > detecting > > > > > > *something*. And once there is something there we shouldn't > > > > > > really get > > > > > > any more timeouts I guess. So probably a totally stupid idea. > > > > > > > > > > Right, if something is connected it would take anyway as much time > > > > > as it > > > > > takes for the sink to reply whether or not we decreased the > > > > > timeout. > > > > > > > > > > However if nothing is connected, we have the excessive timeout > > > > > Khaled > > > > > already noticed (160 * 4ms = 6.4 sec on ICL+). I think to improve > > > > > that > > > > > we could scale the total number of retries by making it > > > > > total_timeout/platform_specific_timeout (letting total_timeout=2sec > > > > > for > > > > > instance) or just changing the drm retry logic to be time based > > > > > instead > > > > > of the number of retries we use atm. > > > > > > > > Doh, reducing simply the HW timeouts would be enough to fix this. > > > > > > What about Lyude's suggestion ( > > > https://patchwork.freedesktop.org/patch/420369/#comment_756572) > > > to drop the retries in intel_dp_aux_xfer() > > > /* Must try at least 3 times according to DP spec */ > > > for (try = 0; try < 5; try++) { > > > > > > And use only the retries in drm_dpcd_access? > > > > I think it would work if we can make the retries configurable and set it > > to > > retries = total_timeout / platform_specific_timeout_per_retry > > > > where total_timeout would be something reasonable like 1 sec. > > I actually think I'm more open to the idea of configurable retries after > learning that apparently this is a thing that the i2c subsystem does - so > there's more precedence for it in the rest of the kernel than I originally > thought. > > I'm still curious if we need these extra retries in here though - there seems to > be one set of retries that is actually platform specific, and then just a random > set of 5 retries that don't seem to have anything to do with platform specific > behavior - so I think it'd still be worth giving a shot at getting rid of that The platform specific part of the timeout is the one desctibed in the maximum timeout values comments. > > > Thanks > > > Khaled > > > > > > > > > > > > > Anyways, this seems about the only thing we can do given the > > > > > > limited > > > > > > hw capabilities. > > > > > > Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > > > > > > > > > > Accordingly disable LTTPR detection until GLK, where the > > > > > > > maximum timeout > > > > > > > we can set is only 1.6ms. > > > > > > > > > > > > > > Link training in the non-transparent mode is known to fail at > > > > > > > least on > > > > > > > some SKL systems with a WD19 dock on the link, which exposes an > > > > > > > LTTPR > > > > > > > (see the References below). While this could have different > > > > > > > reasons > > > > > > > besides the too short AUX timeout used, not detecting LTTPRs > > > > > > > (and so not > > > > > > > using the non-transparent LT mode) fixes link training on these > > > > > > > systems. > > > > > > > > > > > > > > While at it add a code comment about the platform specific > > > > > > > maximum > > > > > > > timeout values. > > > > > > > > > > > > > > v2: Add a comment about the g4x maximum timeout as well. > > > > > > > (Ville) > > > > > > > > > > > > > > Reported-by: Takashi Iwai <tiwai@xxxxxxx> > > > > > > > Reported-and-tested-by: Santiago Zarate < > > > > > > > santiago.zarate@xxxxxxxx> > > > > > > > Reported-and-tested-by: Bodo Graumann <mail@xxxxxxxxxxxxxxx> > > > > > > > References: > > > > > > > https://gitlab.freedesktop.org/drm/intel/-/issues/3166 > > > > > > > Fixes: b30edfd8d0b4 ("drm/i915: Switch to LTTPR non-transparent > > > > > > > mode link training") > > > > > > > Cc: <stable@xxxxxxxxxxxxxxx> # v5.11 > > > > > > > Cc: Takashi Iwai <tiwai@xxxxxxx> > > > > > > > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > > > > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> > > > > > > > --- > > > > > > > drivers/gpu/drm/i915/display/intel_dp_aux.c | 7 +++++++ > > > > > > > .../gpu/drm/i915/display/intel_dp_link_training.c | 15 > > > > > > > ++++++++++++--- > > > > > > > 2 files changed, 19 insertions(+), 3 deletions(-) > > > > > > > > > > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c > > > > > > > b/drivers/gpu/drm/i915/display/intel_dp_aux.c > > > > > > > index eaebf123310a..10fe17b7280d 100644 > > > > > > > --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c > > > > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c > > > > > > > @@ -133,6 +133,7 @@ static u32 g4x_get_aux_send_ctl(struct > > > > > > > intel_dp *intel_dp, > > > > > > > else > > > > > > > precharge = 5; > > > > > > > > > > > > > > +/* Max timeout value on G4x-BDW: 1.6ms */ > > > > > > > if (IS_BROADWELL(dev_priv)) > > > > > > > timeout = DP_AUX_CH_CTL_TIME_OUT_600us; > > > > > > > else > > > > > > > @@ -159,6 +160,12 @@ static u32 skl_get_aux_send_ctl(struct > > > > > > > intel_dp *intel_dp, > > > > > > > enum phy phy = intel_port_to_phy(i915, dig_port- > > > > > > > > base.port); > > > > > > > u32 ret; > > > > > > > > > > > > > > +/* > > > > > > > + * Max timeout values: > > > > > > > + * SKL-GLK: 1.6ms > > > > > > > + * CNL: 3.2ms > > > > > > > + * ICL+: 4ms > > > > > > > + */ > > > > > > > ret = DP_AUX_CH_CTL_SEND_BUSY | > > > > > > > DP_AUX_CH_CTL_DONE | > > > > > > > DP_AUX_CH_CTL_INTERRUPT | > > > > > > > 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 19ba7c7cbaab..c0e25c75c105 100644 > > > > > > > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c > > > > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c > > > > > > > @@ -82,6 +82,18 @@ static void > > > > > > > intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp, > > > > > > > > > > > > > > static bool intel_dp_read_lttpr_common_caps(struct intel_dp > > > > > > > *intel_dp) > > > > > > > { > > > > > > > +struct drm_i915_private *i915 = dp_to_i915(intel_dp); > > > > > > > + > > > > > > > +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 (INTEL_GEN(i915) < 10) > > > > > > > +return false; > > > > > > > + > > > > > > > if (drm_dp_read_lttpr_common_caps(&intel_dp->aux, > > > > > > > intel_dp- > > > > > > > > lttpr_common_caps) < 0) { > > > > > > > memset(intel_dp->lttpr_common_caps, 0, > > > > > > > @@ -127,9 +139,6 @@ int intel_dp_lttpr_init(struct intel_dp > > > > > > > *intel_dp) > > > > > > > bool ret; > > > > > > > int i; > > > > > > > > > > > > > > -if (intel_dp_is_edp(intel_dp)) > > > > > > > -return 0; > > > > > > > - > > > > > > > ret = intel_dp_read_lttpr_common_caps(intel_dp); > > > > > > > if (!ret) > > > > > > > return 0; > > > > > > > -- > > > > > > > 2.25.1 > > > > > > > > > > > > -- > > > > > > Ville Syrjälä > > > > > > Intel > > > > -- > Sincerely, > Lyude Paul (she/her) > Software Engineer at Red Hat > > Note: I deal with a lot of emails and have a lot of bugs on my plate. If you've > asked me a question, are waiting for a review/merge on a patch, etc. and I > haven't responded in a while, please feel free to send me another email to check > on my status. I don't bite! >
