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 4/26/2019 8:07 PM, Ville Syrjälä wrote:
> 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.

Lets make this a bit more clear, may be rename the bit to 
PIPEMISC_HDR_PRECISION_MODE instead?

With that change, this patch is

Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>

>
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