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

["Sharma, Shashank" <shashank.sharma@intel.com>]

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. "

- Shashank

>   	I915_WRITE(PIPEMISC(crtc->pipe), val);
>   }
>   
> diff --git a/drivers/gpu/drm/i915/intel_sprite.h b/drivers/gpu/drm/i915/intel_sprite.h
> index 84be8686be16..500f6bffb139 100644
> --- a/drivers/gpu/drm/i915/intel_sprite.h
> +++ b/drivers/gpu/drm/i915/intel_sprite.h
> @@ -43,13 +43,17 @@ static inline bool icl_is_nv12_y_plane(enum plane_id id)
>   	return false;
>   }
>   
> +static inline u8 icl_hdr_plane_mask(void)
> +{
> +	return BIT(PLANE_PRIMARY) |
> +		BIT(PLANE_SPRITE0) | BIT(PLANE_SPRITE1);
> +}
> +
>   static inline bool icl_is_hdr_plane(struct drm_i915_private *dev_priv,
>   				    enum plane_id plane_id)
>   {
> -	if (INTEL_GEN(dev_priv) < 11)
> -		return false;
> -
> -	return plane_id < PLANE_SPRITE2;
> +	return INTEL_GEN(dev_priv) >= 11 &&
> +		icl_hdr_plane_mask() & BIT(plane_id);
>   }
>   
>   #endif /* __INTEL_SPRITE_H__ */
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