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

[Pandiyan, Dhinakaran]

On Tue, 2016-11-15 at 20:59 +0200, Ville Syrjälä wrote:
> On Mon, Nov 14, 2016 at 09:35:30PM +0000, Pandiyan, Dhinakaran wrote:
> > On Thu, 2016-11-10 at 15:32 -0800, Manasi Navare 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;
> > > 
> > > In the SST equivalent mode_valid function, this variable is named as
> > > max_rate, I think you should name it as max_rate as well for consistency.
> > > Other than that this looks good, we definitely need this for mode validation
> > > at an early stage.
> > > 
> > > Regards
> > > Manasi
> > > 
> > 
> > Well, one of the goals of Patch 1/2 is to reduce ambiguity that has led
> > to some confusing hacks. I prefer clarity over consistency and anyway
> > this variable is local to this function :)
> 
> I'm with Manasi on this one. Consistency wins. We have far too many
> things we call by many names, and that always causes confusion. If you
> think the name isn't good enough, then you should rename it across the
> board.
> 

Alright then, I don't want to bikeshed the variable naming anymore.
Sending another version.


> > 
> > -DK
> > 
> > > > +
> > > > +	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;
> > > > 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
> > > > 
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