[Intel-gfx] [PATCH 2/2] drm/i915/dp: Validate mode against max. link data rate for DP MST

[Pandiyan, Dhinakaran]

On Fri, 2016-11-11 at 19:41 +0200, Ville Syrjälä wrote:
> On Wed, Nov 09, 2016 at 09:32:30PM -0800, Dhinakaran Pandiyan wrote:
> > Not validating the the mode rate against link rate results not pruning
> > invalid modes. For e.g, HBR2 5.4 Gpbs 2 lane configuration does not
> > support 4k @ 60Hz. But, we do not reject this mode currently.
> > 
> > So, make use of the helpers in intel_dp in validate mode rates against
> > max. data rate of a configuration.
> > 
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c     |  4 ++--
> >  drivers/gpu/drm/i915/intel_dp_mst.c | 12 +++++++++++-
> >  drivers/gpu/drm/i915/intel_drv.h    |  2 ++
> >  3 files changed, 15 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 7a9e122..7a73e43 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -161,14 +161,14 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
> >  	return min(source_max, sink_max);
> >  }
> >  
> > -static int
> > +int
> >  intel_dp_link_required(int pixel_clock, int bpp)
> >  {
> >  	/* pixel_clock is in kHz, divide bpp by 8 to return the value in kBps*/
> >  	return (pixel_clock * bpp + 7) / 8;
> >  }
> >  
> > -static int
> > +int
> >  intel_dp_max_data_rate(int max_link_clock, int max_lanes)
> >  {
> >  	/* max_link_clock is the link symbol clock (LS_Clk) in kHz and not the
> > diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> > index 3ffbd69..38d2ce0 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> > @@ -335,7 +335,17 @@ static enum drm_mode_status
> >  intel_dp_mst_mode_valid(struct drm_connector *connector,
> >  			struct drm_display_mode *mode)
> >  {
> > +	struct intel_connector *intel_connector = to_intel_connector(connector);
> > +	struct intel_dp *intel_dp = intel_connector->mst_port;
> >  	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
> > +	int link_clock = intel_dp_max_link_rate(intel_dp);
> > +	int lane_count = drm_dp_max_lane_count(intel_dp->dpcd);
> > +	int bpp = 24; /* MST uses fixed bpp */
> > +	int mode_rate;
> > +	int link_max_data_rate;
> > +
> > +	link_max_data_rate = intel_dp_max_data_rate(link_clock, lane_count);
> > +	mode_rate = intel_dp_link_required(mode->clock, bpp);
> >  
> >  	/* TODO - validate mode against available PBN for link */
> >  	if (mode->clock < 10000)
> > @@ -344,7 +354,7 @@ intel_dp_mst_mode_valid(struct drm_connector *connector,
> >  	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
> >  		return MODE_H_ILLEGAL;
> >  
> > -	if (mode->clock > max_dotclk)
> > +	if (mode_rate > link_max_data_rate || mode->clock > max_dotclk)
> >  		return MODE_CLOCK_HIGH;
> >  
> >  	return MODE_OK;
> 
> You'll also want to fix intel_dp_mst_compute_config(). Actually that one
> should check against the remaining link bw, but we don't track that
> sufficiently well. Well, actually the topology manager does track it,
> but just not atomically so it's not good enough in its current form.
> 
> But as a first step just checking against the total link bw would be an
> improvement.
> 

I am trying to understand why drm_dp_find_vcpi_slots() returns a value
greater than 64  in the 2 lane HBR2, 4k at 60Hz config. Will send out this
patch once that is clear.

-DK


> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index c2f3863..313419d 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -1471,6 +1471,8 @@ 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);
> >  bool intel_dp_read_desc(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);
> >  
> >  /* intel_dp_aux_backlight.c */
> >  int intel_dp_aux_init_backlight_funcs(struct intel_connector *intel_connector);
> > -- 
> > 2.7.4
>