[Intel-gfx] [PATCH v4 2/2] drm/i915/dp: Extend BDW DP audio workaround to GEN9 platforms

[Pandiyan, Dhinakaran]

On Tue, 2016-11-01 at 21:35 +0200, Jani Nikula wrote:
> On Tue, 01 Nov 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com> wrote:
> > According to BSpec, cdclk for BDW has to be not less than 432 MHz with DP
> > audio enabled, port width x4, and link rate HBR2 (5.4 GHz). With cdclk less
> > than 432 MHz, enabling audio leads to pipe FIFO underruns and displays
> > cycling on/off.
> >
> > Let's apply this work around to GEN9 platforms too, as it fixes the same
> > issue.
> 
> I'm too tired to read bspec now, but is gen9 really the answer, or just
> Skylake?
> 
> 

Gen9, applies to BXT and KBL as well. 

-DK

> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97907
> > Cc: stable at vger.kernel.org
> > Cc: Libin Yang <libin.yang at linux.intel.com>
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 37483ee..c0ae147 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -10264,8 +10264,10 @@ static void bxt_modeset_commit_cdclk(struct drm_atomic_state *old_state)
> >  static int bdw_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
> >  					  int pixel_rate)
> >  {
> > +	struct drm_device *dev = crtc_state->base.crtc->dev;
> 
> Nitpick, I guess I'd make that
> 
> 	struct drm_i915_private *dev_priv = to_i915(crtc_state->base.crtc->dev);
> 
> but no big deal.
> 
> > +
> >  	/* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
> > -	if (crtc_state->ips_enabled)
> > +	if (IS_BROADWELL(to_i915(dev)) && crtc_state->ips_enabled)
> >  		pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
> >  
> >  	/* BSpec says "Do not use DisplayPort with CDCLK less than
> > @@ -10307,7 +10309,7 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
> >  
> >  		pixel_rate = ilk_pipe_pixel_rate(crtc_state);
> >  
> > -		if (IS_BROADWELL(dev_priv))
> > +		if (IS_BROADWELL(dev_priv) || IS_GEN9(dev_priv))
> >  			pixel_rate = bdw_adjust_min_pipe_pixel_rate(crtc_state,
> >  								    pixel_rate);
>