Re: [Intel-gfx] [PATCH 20/20] drm/i915/dp: Disable DFP RGB->YCbCr conversion for now

From: "Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 20/20] drm/i915/dp: Disable DFP RGB->YCbCr conversion for now
Date: Fri, 10 Dec 2021 11:34:29 +0530	[thread overview]
Message-ID: <7fcd7e4f-7d5b-c834-8e18-0414b9af0251@intel.com> (raw)
In-Reply-To: <YXkTvw2SQCxIFm+S@intel.com>

On 10/27/2021 2:24 PM, Ville Syrjälä wrote:
> On Wed, Oct 27, 2021 at 12:57:37PM +0530, Nautiyal, Ankit K wrote:
>> On 10/15/2021 7:09 PM, Ville Syrjala wrote:
>>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>
>>> We lack sufficient state tracking to figure out whether
>>> we want the DFP to perform the RGB->YCbCr conversion for us
>>> or not. So currently we are blindly just enabling that all the
>>> time when supported by the DFP. That is nonsense. So until
>>> we imporve our state tracking for this just disable the feature.
>>>
>>> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
>>> Cc: Uma Shankar <uma.shankar@intel.com>
>>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/display/intel_dp.c | 10 ++++++++++
>>>    1 file changed, 10 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>>> index 29b12456c461..3e2a29b589a9 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>>> @@ -1107,6 +1107,7 @@ static bool intel_dp_supports_dsc(struct intel_dp *intel_dp,
>>>    static bool intel_dp_is_ycbcr420(struct intel_dp *intel_dp,
>>>    				 const struct intel_crtc_state *crtc_state)
>>>    {
>>> +	/* FIXME see intel_dp_update_420() regarding rgb_to_ycbcr */
>>>    	return crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 ||
>>>    		(crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR444 &&
>>>    		 intel_dp->dfp.ycbcr_444_to_420);
>>> @@ -2456,6 +2457,7 @@ void intel_dp_configure_protocol_converter(struct intel_dp *intel_dp,
>>>    			    "Failed to %s protocol converter YCbCr 4:2:0 conversion mode\n",
>>>    			    enabledisable(intel_dp->dfp.ycbcr_444_to_420));
>>>    
>>> +	/* FIXME see intel_dp_update_420() regarding rgb_to_ycbcr */
>>>    	tmp = intel_dp->dfp.rgb_to_ycbcr ?
>>>    		DP_CONVERSION_BT709_RGB_YCBCR_ENABLE : 0;
>>>    
>>> @@ -4261,6 +4263,14 @@ intel_dp_update_420(struct intel_dp *intel_dp)
>>>    	rgb_to_ycbcr = drm_dp_downstream_rgb_to_ycbcr_conversion(intel_dp->dpcd,
>>>    								 intel_dp->downstream_ports,
>>>    								 DP_DS_HDMI_BT709_RGB_YCBCR_CONV);
>>> +	/*
>>> +	 * FIXME need to actually track whether we're really
>>> +	 * going to be doing the RGB->YCbCr connversion or not.
>>> +	 * We can't tell by simply looking at intel_dp->dfp.rgb_to_ycbcr.
>>> +	 * Readout is going to annoying due to having to read that
>>> +	 * state from external hardware that may vanish at any time :(
>>> +	 */
>>
>> Hmm right. Do you have any suggestion what should be the better place
>> for defining the policy for using DFPs CSC or use our own HW, in case of
>> YCbCr 420 output?
> One idea that came to mind was just adding some kind of
> sink_format thing into the crtc_state, and computing that appropriately
> during .compute_config(). But as mentioned the readout part is going to
> be annoying. Maybe we just won't have readout for it.

Agreed.

As mentioned in the FIX ME, lets have dfp->rgb_to_ycbcr only to capture 
that the dfp supports conversion.

and dfp->ycbcr_444_420 to capture that it supports 444_420.

Whether we need to program the DPCD to avail these support can be 
captured in another member to crtc_state->dp_dfp_444_420, and 
crtc_state->dp_dfp_rgb_ycbcr based on crtc_state->sink_format.

We can fill these members, during compute_config along with dsc 
considerations.

These can then be used in dp_configure_protocol_converter().

Regards,

Ankit