[Intel-gfx] [PATCH v2 5/6] drm/i915: Avoid a full port detection in the first eDP short pulse

[Dhinakaran Pandiyan]

On Thu, 2018-10-11 at 16:21 +0300, Ville Syrjälä wrote:
> On Wed, Oct 10, 2018 at 05:41:23PM -0700, José Roberto de Souza
> wrote:
> > Some eDP panels do not set a valid sink count value and even for
> > the
> > ones that sets is should always be one for eDP, that is why it is
> > not
> > cached in intel_edp_init_dpcd().
> > 
> > But intel_dp_short_pulse() compares the old count with the read one
> > if there is a mistmatch a full port detection will be executed,
> > what
> > was happening in the first short pulse interruption of eDP panels
> > that sets sink count.
> > 
> > Instead of just skip the compasison for eDP panels, lets not read
> > the sink count at all for eDP.
> > 
> > v2: the previous version of this patch was caching the sink count
> > in intel_edp_init_dpcd() but I was pointed out by Ville a patch
> > that
> > handled a case of a eDP panel that do not set sink count
> > 
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 44 +++++++++++++++++++--------
> > ------
> >  1 file changed, 26 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > index 13ff89be6ad6..1826d491efd7 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4034,8 +4034,6 @@ intel_edp_init_dpcd(struct intel_dp
> > *intel_dp)
> >  static bool
> >  intel_dp_get_dpcd(struct intel_dp *intel_dp)
> >  {
> > -	u8 sink_count;
> > -
> >  	if (!intel_dp_read_dpcd(intel_dp))
> >  		return false;
> >  
> > @@ -4045,25 +4043,35 @@ intel_dp_get_dpcd(struct intel_dp
> > *intel_dp)
> >  		intel_dp_set_common_rates(intel_dp);
> >  	}
> >  
> > -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT,
> > &sink_count) <= 0)
> > -		return false;
> > -
> >  	/*
> > -	 * Sink count can change between short pulse hpd hence
> > -	 * a member variable in intel_dp will track any changes
> > -	 * between short pulse interrupts.
> > +	 * Some eDP panels do not set a valid value for sink count,
> > that is why
> > +	 * it don't care about read it here and in
> > intel_edp_init_dpcd().
> 
> Can't quite parse that.
> 
> "Some eDP panels do not set a valid value
>  for sink count, so we ignore it."
> 
> or something like that perhaps.
> 
> >  	 */
> > -	intel_dp->sink_count = DP_GET_SINK_COUNT(sink_count);
> > +	if (!intel_dp_is_edp(intel_dp)) {
> > +		u8 count;
> > +		ssize_t r;
> >  
> > -	/*
> > -	 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies
> > that
> > -	 * a dongle is present but no display. Unless we require to
> > know
> > -	 * if a dongle is present or not, we don't need to update
> > -	 * downstream port information. So, an early return here saves
> > -	 * time from performing other operations which are not
> > required.
> > -	 */
> > -	if (!intel_dp_is_edp(intel_dp) && !intel_dp->sink_count)
> > -		return false;
> > +		r = drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT,
> > &count);
> > +		if (r < 1)
> > +			return false;
> 
> My earlier suggestion was that we should keep reading this
> anyway because some cts maybe required it. Would at least
> avoid mixing in two functional changes into once patch.

Documenting the outcome of IRC discussion so that we are on the same
page -  CTS does not test eDP, hence it is okay to skip reading sink
count for eDP panels. 



> 
> > +
> > +		/*
> > +		 * Sink count can change between short pulse hpd hence
> > +		 * a member variable in intel_dp will track any changes
> > +		 * between short pulse interrupts.
> > +		 */
> > +		intel_dp->sink_count = DP_GET_SINK_COUNT(count);
> > +
> > +		/*
> > +		 * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1
> > implies that
> > +		 * a dongle is present but no display. Unless we
> > require to know
> > +		 * if a dongle is present or not, we don't need to
> > update
> > +		 * downstream port information. So, an early return
> > here saves
> > +		 * time from performing other operations which are not
> > required.
> > +		 */
> > +		if (!intel_dp->sink_count)
> > +			return false;
> > +	}
> >  
> >  	if (!drm_dp_is_branch(intel_dp->dpcd))
> >  		return true; /* native DP sink */
> > -- 
> > 2.19.1
> 
>