Re: [PATCH v5] drm/i915/edp: Be less aggressive about changing link config on eDP

Manasi Navare
2017-08-17T19:45:16Z

On Thu, Aug 17, 2017 at 12:20:03PM -0700, Manasi Navare wrote:
> On Thu, Aug 17, 2017 at 10:50:04AM -0700, Jim Bride wrote:
> > On Wed, Aug 16, 2017 at 03:13:06PM -0700, Manasi Navare wrote:
> > > On Wed, Aug 09, 2017 at 02:21:07PM -0700, Jim Bride wrote:
> > > > This set of changes has some history to them. There were several attempts
> > > > to add what was called "fast link training" to i915, which actually wasn't
> > > > fast link training as per the DP spec. These changes were:
> > > >
> > > > commit 5fa836a9d859 ("drm/i915: DP link training optimization")
> > > > commit 4e96c97742f4 ("drm/i915: eDP link training optimization")
> > > >
> > > > which were eventually hand-reverted by:
> > > >
> > > > commit 34511dce4b35 ("drm/i915: Revert DisplayPort fast link training
> > > > feature")
> > > >
> > > > in kernel 4.7-rc4. The eDP pieces of the above revert, however, had some
> > > > very bad side-effects on PSR functionality on Skylake. The issue at
> > > > hand is that when PSR exits i915 briefly emits TP1 followed by TP2/3
> > > > (depending on the original link configuration) in order to quickly get
> > > > the source and sink back in synchronization across the link before handing
> > > > control back to the i915. There's an assumption that none of the link
> > > > configuration information has changed (and thus it's still valid) since the
> > > > last full link training operation. The revert above was identified via a
> > > > bisect as the cause of some of Skylake's PSR woes. This patch, largely
> > > > based on commit 4e96c97742f4 ("drm/i915: eDP link training optimization")
> > > > puts the eDP portions of this patch back in place. None of the flickering
> > > > issues that spurred the revert have been seen, and I suspect the real
> > > > culprits here were addressed by some of the recent link training changes
> > > > that Manasi has implemented, and PSR on Skylake is definitely more happy
> > > > with these changes in-place.
> > > >
> > > > v2 and v3: Rebase
> > > > v4: * Clean up accesses to train_set_valid a bit for easier
> > > > reading. (Chris)
> > > > * Rebase
> > > > v5: * Checkpatch cleanup
> > > > * Rebase
> > > >
> > > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > > Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > > > Cc: Manasi D Navare <manasi.d.navare@intel.com>
> > > > Cc: Mika Kahola <mika.kahola@intel.com>
> > > > Cc: Jani Nikula <jani.nikula@intel.com>
> > > > Fixes: 34511dce4 ("drm/i915: Revert DisplayPort fast link training feature")
> > > > Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
> > > > ---
> > > > drivers/gpu/drm/i915/intel_dp.c | 4 +++-
> > > > drivers/gpu/drm/i915/intel_dp_link_training.c | 15 ++++++++++++++-
> > > > drivers/gpu/drm/i915/intel_drv.h | 2 ++
> > > > 3 files changed, 19 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > > index 76c8a0b..4bd409c 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > @@ -106,7 +106,7 @@ static const int default_rates[] = { 162000, 270000, 540000 };
> > > > * If a CPU or PCH DP output is attached to an eDP panel, this function
> > > > * will return true, and false otherwise.
> > > > */
> > > > -static bool is_edp(struct intel_dp *intel_dp)
> > > > +bool is_edp(struct intel_dp *intel_dp)

I also need this function to be exposed to files outside of intel_dp.c
for the patch:
https://patchwork.freedesktop.org/series/28900/
But one of the review comments I got is to prefix the name of this function with intel_dp
when exposing it to outside of intel_dp.c which makes sense as per the naming conventions
of the other functions. But we already have a function intel_dp_is_edp() used to get VBT information.
Any suggestions for the name? And do you want to make this change as part of your series so
I can rebase my patch on top of this?

Regards
Manasi

> > > > {
> > > > struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> > > >
> > > > @@ -4711,6 +4711,7 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
> > > > intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> > > >
> > > > intel_dp->reset_link_params = false;
> > > > + intel_dp->train_set_valid = false;
> > > > }
> > > >
> > > > intel_dp_print_rates(intel_dp);
> > > > @@ -5979,6 +5980,7 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
> > > > intel_dp_set_source_rates(intel_dp);
> > > >
> > > > intel_dp->reset_link_params = true;
> > > > + intel_dp->train_set_valid = false;
> > > > intel_dp->pps_pipe = INVALID_PIPE;
> > > > intel_dp->active_pipe = INVALID_PIPE;
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > > index 05907fa..67032cf 100644
> > > > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > > > @@ -94,7 +94,8 @@ static bool
> > > > intel_dp_reset_link_train(struct intel_dp *intel_dp,
> > > > uint8_t dp_train_pat)
> > > > {
> > > > - memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> > > > + if (!intel_dp->train_set_valid)
> > > > + memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> > > > intel_dp_set_signal_levels(intel_dp);
> > > > return intel_dp_set_link_train(intel_dp, dp_train_pat);
> > > > }
> > > > @@ -162,9 +163,18 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
> > > > DP_TRAINING_PATTERN_1 |
> > > > DP_LINK_SCRAMBLING_DISABLE)) {
> > > > DRM_ERROR("failed to enable link training\n");
> > > > + intel_dp->train_set_valid = false;
> > > > return false;
> > > > }
> > > >
> > > > + /*
> > > > + * The initial set of link parameters are set by this point, so go
> > > > + * ahead and set intel_dp->train_set_valid to false in case any of
> > > > + * the succeeding steps fail. It will be set back to true if we were
> > > > + * able to achieve clock recovery in the specified configuration.
> > > > + */
> > > > + intel_dp->train_set_valid = false;
> > > > +
> > > > voltage_tries = 1;
> > > > max_vswing_tries = 0;
> > > > for (;;) {
> > > > @@ -179,6 +189,7 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
> > > >
> > > > if (drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count)) {
> > > > DRM_DEBUG_KMS("clock recovery OK\n");
> > > > + intel_dp->train_set_valid = is_edp(intel_dp);
> > > > return true;
> > > > }
> > > >
> > > > @@ -256,6 +267,7 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
> > > > training_pattern |
> > > > DP_LINK_SCRAMBLING_DISABLE)) {
> > > > DRM_ERROR("failed to start channel equalization\n");
> > > > + intel_dp->train_set_valid = false;
> > > > return false;
> > > > }
> > > >
> > > > @@ -296,6 +308,7 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
> > > > /* Try 5 times, else fail and try at lower BW */
> > > > if (tries == 5) {
> > > > intel_dp_dump_link_status(link_status);
> > > > + intel_dp->train_set_valid = false;
> > > > DRM_DEBUG_KMS("Channel equalization failed 5 times\n");
> > > > }
> > >
> > > There are other cases in the channel equalization loop of 5 tries where if drm_dp_clock_recover_ok
> > > is not true then it just breaks from the for loop. Same in case of failure to update link train or
> > > failure to get link status. In this case we dont set train_set_valid to false sinec the tries is not 5 yet
> > > In this case since the train_set_valid was true when it entered this function, it will
> > > stay true without actually succeeding at ch eq.
> > > Shouldnt we be setting train_set_valid to false in these cases?
> > > Or is there something I am missing here?
> >
> > It's set to false before all of those, and then set back to true if the
> > retrain works and we're on eDP. Making the change to do this was some
> > review feedback from Chris on an earlier version of the patch.
> >
> > Jim
> >
> >
>
> I see that it is set to false before starting the clock recovery but after clock recovery
> succeeds, this is set to true and only then you will proceed with channel equalization.
> And in channel equalization, it never gets set to false in case of the failures I mentioned above since
> we just break there.
> It then gets set to false only if the tries are 5 but it should also be set to false in case
> of other failures that I mentioned else we will end up leaving it to true even when channel EQ never
> succeeded.
>
> Manasi
>
> > > Regards
> > > Manasi
> > >
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > > > index f91de9c..792bf547 100644
> > > > --- a/drivers/gpu/drm/i915/intel_drv.h
> > > > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > > > @@ -994,6 +994,7 @@ struct intel_dp {
> > > > struct drm_dp_aux aux;
> > > > enum intel_display_power_domain aux_power_domain;
> > > > uint8_t train_set[4];
> > > > + bool train_set_valid;
> > > > int panel_power_up_delay;
> > > > int panel_power_down_delay;
> > > > int panel_power_cycle_delay;
> > > > @@ -1548,6 +1549,7 @@ static inline unsigned int intel_dp_unused_lane_mask(int lane_count)
> > > > }
> > > >
> > > > bool intel_dp_read_dpcd(struct intel_dp *intel_dp);
> > > > +bool is_edp(struct intel_dp *intel_dp);
> > > > int intel_dp_link_required(int pixel_clock, int bpp);
> > > > int intel_dp_max_data_rate(int max_link_clock, int max_lanes);
> > > > bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
> > > > --
> > > > 2.7.4
> > > >
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