Re: [PATCH 2/2] drm/i915: Enable pipe HDR mode on ICL if only HDR planes are used

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Apr 26, 2019 at 06:40:11PM +0530, Sharma, Shashank wrote:
> 
> On 4/13/2019 12:00 AM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > The pipe has a special HDR mode with higher precision when only
> > HDR planes are active. Let's use it.
> >
> > Curiously this fixes the kms_color gamma/degamma tests when
> > using a HDR plane, which is always the case unless one hacks
> > the test to use an SDR plane. If one does hack the test to use
> > an SDR plane it does pass already.
> >
> > I have no actual explanation how the output after the gamma
> > LUT can be different between the two modes. The way the tests
> > are written should mean that the output should be identical
> > between the solid color vs. the gradient. But clearly that
> > somehow doesn't hold true for the HDR planes in non-HDR pipe
> > mode. Anyways, as long as we stick to one type of plane the
> > test should produce sensible results now.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_reg.h      |  1 +
> >   drivers/gpu/drm/i915/intel_display.c |  7 +++++++
> >   drivers/gpu/drm/i915/intel_sprite.h  | 12 ++++++++----
> >   3 files changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index 8ad2f0a03f28..90d60ecd3317 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -5767,6 +5767,7 @@ enum {
> >   #define _PIPE_MISC_B			0x71030
> >   #define   PIPEMISC_YUV420_ENABLE	(1 << 27)
> >   #define   PIPEMISC_YUV420_MODE_FULL_BLEND (1 << 26)
> > +#define   PIPEMISC_HDR_MODE		(1 << 23) /* icl+ */
> >   #define   PIPEMISC_OUTPUT_COLORSPACE_YUV  (1 << 11)
> >   #define   PIPEMISC_DITHER_BPC_MASK	(7 << 5)
> >   #define   PIPEMISC_DITHER_8_BPC		(0 << 5)
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 490bd49ff42a..d0dbdbd5db3f 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -4055,6 +4055,9 @@ static void intel_update_pipe_config(const struct intel_crtc_state *old_crtc_sta
> >   			ironlake_pfit_disable(old_crtc_state);
> >   	}
> >   
> > +	if (INTEL_GEN(dev_priv) >= 9 || IS_BROADWELL(dev_priv))
> > +		bdw_set_pipemisc(new_crtc_state);
> > +
> >   	if (INTEL_GEN(dev_priv) >= 11)
> >   		icl_set_pipe_chicken(crtc);
> >   }
> > @@ -8869,6 +8872,10 @@ static void bdw_set_pipemisc(const struct intel_crtc_state *crtc_state)
> >   		val |= PIPEMISC_YUV420_ENABLE |
> >   			PIPEMISC_YUV420_MODE_FULL_BLEND;
> >   
> > +	if (INTEL_GEN(dev_priv) >= 11 &&
> > +	    (crtc_state->active_planes & ~icl_hdr_plane_mask()) == 0)
> > +		val |= PIPEMISC_HDR_MODE;
> > +
> 
> Shouldn't we check if the content being played on plane is HDR before 
> enabling this bit (even though I am not sure if there is any harm in 
> doing that)? Or maybe check the connector->output_hdr_metadata ? Most of 
> the times we would be sending SDR buffers on this plane. What happens 
> exactly when we set this bit ? The bspec says:
> 
> "This field enables the HDR mode, allowing for higher precision output 
> from the HDR supporting planes and bypassing the SDR planes in blending. "

I think the bit is just misnamed (like most things with "HDR" in their
name). It's just a "gimme moar precision" bit.


-- 
Ville Syrjälä
Intel
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