On Tue, 16 Mar 2021 17:54:26 +0100, 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). > > 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. > > Reported-by: Takashi Iwai <tiwai@xxxxxxx> > 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> > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> Thanks! I'm now building a test kernel and ask people testing it. https://apibugzilla.suse.com/show_bug.cgi?id=1183294 BTW, the patch isn't applicable cleanly to 5.11.x kernel as is. The file intel_dp_aux.c needs to be changed to intel_dp.c. Hopefully Greg can manage the file rename. Takashi > --- > drivers/gpu/drm/i915/display/intel_dp_aux.c | 7 +++++++ > drivers/gpu/drm/i915/display/intel_dp_link_training.c | 8 ++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c > index eaebf123310a..b581e8acce07 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 ILK-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..de6d70a29b47 100644 > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c > @@ -123,10 +123,18 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable) > */ > int intel_dp_lttpr_init(struct intel_dp *intel_dp) > { > + struct drm_i915_private *i915 = dp_to_i915(intel_dp); > int lttpr_count; > bool ret; > int i; > > + /* > + * 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 0; > + > if (intel_dp_is_edp(intel_dp)) > return 0; > > -- > 2.25.1 >
