Re: [PATCH 2/2] drm/i915/lspcon: Add workaround for resuming in PCON mode

Imre Deak
2016-10-20T21:41:11Z

On Thu, 2016-10-20 at 23:50 +0300, Jani Nikula wrote:
> On Thu, 20 Oct 2016, Imre Deak <imre.deak@intel.com> wrote:
> > On Thu, 2016-10-20 at 22:24 +0300, Jani Nikula wrote:
> > > On Thu, 20 Oct 2016, Jani Nikula <jani.nikula@intel.com> wrote:
> > > > On Thu, 20 Oct 2016, Imre Deak <imre.deak@intel.com> wrote:
> > > > > On my APL the LSPCON firmware resumes in PCON mode as opposed to the
> > > > > expected LS mode. It also appears to be in a state where AUX DPCD reads
> > > > > will succeed but return garbage recovering only after a few hundreds of
> > > > > milliseconds. After the recovery time DPCD reads will result in the
> > > > > correct values and things will continue to work. If I2C over AUX is
> > > > > attempted during this recovery time (implying an AUX write transaction)
> > > > > the firmware won't recover and will stay in this broken state.
> > > > >
> > > > > As a workaround check if the firmware is in PCON state after resume and
> > > > > if so wait until the correct DPCD values are returned. For this we
> > > > > compare the branch descriptor with the one we cached during init time.
> > > > > If the firmware was in the LS state, we skip the w/a and continue as
> > > > > before.
> > > > >
> > > > > Cc: Shashank Sharma <shashank.sharma@intel.com>
> > > > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > > Cc: Jani Nikula <jani.nikula@intel.com>
> > > > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/intel_dp.c     |  2 +-
> > > > >  drivers/gpu/drm/i915/intel_drv.h    |  6 ++++-
> > > > >  drivers/gpu/drm/i915/intel_lspcon.c | 52 ++++++++++++++++++++++++++++++-------
> > > > >  3 files changed, 48 insertions(+), 12 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > > > index e90211e..ec031db 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > > @@ -3487,7 +3487,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
> > > > >   intel_dp->DP = DP;
> > > > >  }
> > > > >
> > > > > -static bool
> > > > > +bool
> > > > >  intel_dp_read_dpcd(struct intel_dp *intel_dp)
> > > > >  {
> > > > >   if (drm_dp_dpcd_read(&intel_dp->aux, 0x000, intel_dp->dpcd,
> > > > > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > > > > index a35e241..9a2366e 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_drv.h
> > > > > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > > > > @@ -972,7 +972,9 @@ struct intel_dp {
> > > > >  struct intel_lspcon {
> > > > >   bool active;
> > > > >   enum drm_lspcon_mode mode;
> > > > > - struct drm_dp_aux *aux;
> > > > > + struct intel_dp *intel_dp;
> > > > > + bool desc_valid;
> > > > > + struct intel_dp_desc desc;
> > > >
> > > > I guess we could cache the desc in intel_dp directly. Independent of
> > > > this patch.
> > > >
> > > > Also, I'm wondering if we could stick with just aux here, and read
> > > > something else from dpcd instead.
> > > >
> > > > >  };
> > > > >
> > > > >  struct intel_digital_port {
> > > > > @@ -1469,6 +1471,8 @@ static inline unsigned int intel_dp_unused_lane_mask(int lane_count)
> > > > >  }
> > > > >
> > > > >  bool
> > > > > +intel_dp_read_dpcd(struct intel_dp *intel_dp);
> > > > > +bool
> > > > >  intel_dp_read_desc(struct intel_dp *intel_dp, struct intel_dp_desc *desc);
> > > > >  void
> > > > >  intel_dp_print_desc(struct intel_dp *intel_dp, struct intel_dp_desc *desc);
> > > > > diff --git a/drivers/gpu/drm/i915/intel_lspcon.c b/drivers/gpu/drm/i915/intel_lspcon.c
> > > > > index d2c8cb2..54c6173 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_lspcon.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_lspcon.c
> > > > > @@ -30,7 +30,7 @@
> > > > >  static enum drm_lspcon_mode lspcon_get_current_mode(struct intel_lspcon *lspcon)
> > > > >  {
> > > > >   enum drm_lspcon_mode current_mode = DRM_LSPCON_MODE_INVALID;
> > > > > - struct i2c_adapter *adapter = &lspcon->aux->ddc;
> > > > > + struct i2c_adapter *adapter = &lspcon->intel_dp->aux.ddc;
> > > > >
> > > > >   if (drm_lspcon_get_mode(adapter, ¤t_mode))
> > > > >   DRM_ERROR("Error reading LSPCON mode\n");
> > > > > @@ -45,7 +45,7 @@ static int lspcon_change_mode(struct intel_lspcon *lspcon,
> > > > >  {
> > > > >   int err;
> > > > >   enum drm_lspcon_mode current_mode;
> > > > > - struct i2c_adapter *adapter = &lspcon->aux->ddc;
> > > > > + struct i2c_adapter *adapter = &lspcon->intel_dp->aux.ddc;
> > > > >
> > > > >   err = drm_lspcon_get_mode(adapter, ¤t_mode);
> > > > >   if (err) {
> > > > > @@ -72,7 +72,7 @@ static int lspcon_change_mode(struct intel_lspcon *lspcon,
> > > > >  static bool lspcon_probe(struct intel_lspcon *lspcon)
> > > > >  {
> > > > >   enum drm_dp_dual_mode_type adaptor_type;
> > > > > - struct i2c_adapter *adapter = &lspcon->aux->ddc;
> > > > > + struct i2c_adapter *adapter = &lspcon->intel_dp->aux.ddc;
> > > > >
> > > > >   /* Lets probe the adaptor and check its type */
> > > > >   adaptor_type = drm_dp_dual_mode_detect(adapter);
> > > > > @@ -89,8 +89,42 @@ static bool lspcon_probe(struct intel_lspcon *lspcon)
> > > > >   return true;
> > > > >  }
> > > > >
> > > > > +static void lspcon_resume_in_pcon_wa(struct intel_lspcon *lspcon)
> > > > > +{
> > > > > + unsigned long start = jiffies;
> > > > > +
> > > > > + if (!lspcon->desc_valid)
> > > > > + return;
> > > > > +
> > > > > + while (1) {
> > > > > + struct intel_dp_desc desc;
> > > > > +
> > > > > + /*
> > > > > +  * The w/a only applies in PCON mode and we don't expect any
> > > > > +  * AUX errors.
> > > > > +  */
> > > > > + if (!intel_dp_read_desc(lspcon->intel_dp, &desc))
> > > > > + return;
> > > > > +
> > > > > + if (!memcmp(&lspcon->desc, &desc, sizeof(desc))) {
> > > > > + DRM_DEBUG_KMS("LSPCON recovering in PCON mode after %u ms\n",
> > > > > +       jiffies_to_msecs(jiffies - start));
> > > > > + return;
> > > > > + }
> > > > > +
> > > > > + if (time_after(jiffies, start + msecs_to_jiffies(1000)))
> > > > > + break;
> > > > > +
> > > > > + msleep(10);
> > > > > + }
> > > > > +
> > > > > + DRM_DEBUG_KMS("LSPCON DP descriptor mismatch after resume\n");
> > > > > +}
> > > >
> > > > I think we need to go through the LSPCON spec once more before we merge
> > > > this. Maybe we don't reset the LSPCON properly. Maybe we don't handle
> > > > the resume properly. Maybe this isn't a "workaround" after all.
> > >
> > > Looks like this stuff is normal behaviour if the LSPCON has been in low
> > > power state, and we need to wake it up. In PCON mode, this is done using
> > > DP_SET_POWER. And while waking up, it'll issue AUX DEFER, as we can see
> > > from the logs.
> >
> > I did think about that, but waking the device via DP_SET_POWER(D0)
> > didn't help. Doing any AUX write transactions actually gets the device
> > into a stuck state for good (until next reboot on APL).
> >
> > More over, we don't get AUX DEFERs the AUX transactions succeed, it's
> > only that reads will return corrupted values for the given time period.
>
> The bug at hand has native defers
> https://bugs.freedesktop.org/show_bug.cgi?id=98353

For I2C-over-AUX I also get defers, but not for DPCD transactions for
native AUX registers for instance DP_SET_POWER or the OUI, device-ID
registers. I also tried the LS mode wake-up sequence via
I2C-over-AUX (offset 0x20), but didn't help either.

The bug above could be a different issue, although I did see this
particular scenario getting fixed on the same machine see
/archive/results/CI_IGT_test/Patchwork_2778/

--Imre