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

[Imre Deak <imre.deak@intel.com>]

On Fri, 2016-10-21 at 11:16 +0530, Sharma, Shashank wrote:
> Regards
> 
> Shashank
> 
> 
> On 10/21/2016 12:50 AM, Imre Deak wrote:
> > On Thu, 2016-10-20 at 21:20 +0300, Jani Nikula 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;
> IMHO, Its not required to have the intel_dp inside lspcon. we can always 
> get intel_dig_port from lspcon, and intel_dp from intel_dig_port

Yea I missed that, so the above change isn't needed, I'll fix this.

> The reason why I kept aux here was thats the only thing required to 
> read/write from/to lspcon.
> > > > +	bool desc_valid;
> > > > +	struct intel_dp_desc desc;
> > > I guess we could cache the desc in intel_dp directly. Independent of
> > > this patch.
> > It's not used anywhere else, but I can move it to intel_dp.
> > 
> > > Also, I'm wondering if we could stick with just aux here, and read
> > > something else from dpcd instead.
> > Not sure either, I picked desc since we read it out anyway during init.
> > 
> > > >   };
> > > >   
> > > >   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.
> > I haven't found at least any way to reset things. I also tried to
> > change to LS mode when suspending or switch here to LS mode first and
> > only then to PCON mode but these didn't help.
> > 
> > --Imre
> I agree with Imre. There is nothing like that in specs as such, and even 
> If this was something missing during the reset/power down time, we 
> should have seen this on all/most of the boards.
> 
> Regards
> Shashank
> > 
> > > Maybe this isn't a "workaround" after all.
> > > 
> > > BR,
> > > Jani.
> > > 
> > > > +
> > > >   void lspcon_resume(struct intel_lspcon *lspcon)
> > > >   {
> > > > +	lspcon_resume_in_pcon_wa(lspcon);
> > > > +
> > > >   	if (lspcon_change_mode(lspcon, DRM_LSPCON_MODE_PCON, true))
> > > >   		DRM_ERROR("LSPCON resume failed\n");
> > > >   	else
> > > > @@ -111,7 +145,7 @@ bool lspcon_init(struct intel_digital_port *intel_dig_port)
> > > >   
> > > >   	lspcon->active = false;
> > > >   	lspcon->mode = DRM_LSPCON_MODE_INVALID;
> > > > -	lspcon->aux = &dp->aux;
> > > > +	lspcon->intel_dp = dp;
> > > >   
> > > >   	if (!lspcon_probe(lspcon)) {
> > > >   		DRM_ERROR("Failed to probe lspcon\n");
> > > > @@ -131,12 +165,10 @@ bool lspcon_init(struct intel_digital_port *intel_dig_port)
> > > >   		}
> > > >   	}
> > > >   
> > > > -	if (drm_debug & DRM_UT_KMS) {
> > > > -		struct intel_dp_desc desc;
> > > > -
> > > > -		if (intel_dp_read_desc(dp, &desc))
> > > > -			intel_dp_print_desc(dp, &desc);
> > > > -	}
> > > > +	lspcon->desc_valid = intel_dp_read_dpcd(dp) &&
> > > > +			     intel_dp_read_desc(dp, &lspcon->desc);
> > > > +	if ((drm_debug & DRM_UT_KMS) && lspcon->desc_valid)
> > > > +		intel_dp_print_desc(dp, &lspcon->desc);
> > > >   
> > > >   	DRM_DEBUG_KMS("Success: LSPCON init\n");
> > > >   	return true;
> 
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