Re: [PATCH v3] drm/i915/display: Use the recomended min_hblank values

["Murthy, Arun R" <arun.r.murthy@intel.com>]

On 25-06-2025 22:59, Imre Deak wrote:
> On Wed, Jun 25, 2025 at 11:04:07AM +0530, Arun R Murthy wrote:
>> Use recommended values as per wa_14021694213 to compare with the
>> calculated value and choose minimum of them.
>>
>> v2: corrected checkpatch warning and retain the restriction for
>> min_hblank (Jani)
>> v3: use calculated value to compare with recomended value and choose
>> minimum of them (Imre)
>>
>> Bspec: 74379
>> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
>> ---
>> Changes in v3:
>> - EDITME: describe what is new in this series revision.
>> - EDITME: use bulletpoints and terse descriptions.
>> - Link to v2: https://lore.kernel.org/r/20250624-min_hblank-v2-1-9110a9342d8c@intel.com
>>
>> Changes in v2:
>> - EDITME: describe what is new in this series revision.
>> - EDITME: use bulletpoints and terse descriptions.
>> - Link to v1: https://lore.kernel.org/r/20250624-min_hblank-v1-1-5c100e4a8b05@intel.com
> The above 'Changes in vx' templates could be removed imo.
>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 17 ++++++++++++++++-
>>   1 file changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index f48912f308df7fd26c9d089e8f1bd096bfc8df95..c55315fb74734fded40695bae40dd19f71a9786f 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -3175,7 +3175,22 @@ int intel_dp_compute_min_hblank(struct intel_crtc_state *crtc_state,
>>   	 */
>>   	min_hblank = min_hblank - 2;
>>   
>> -	min_hblank = min(10, min_hblank);
>> +	/*
>> +	 * min_hblank formula is undergoing a change, to avoid underrun use the
>> +	 * recomended value in spec to compare with the calculated one and use the
>> +	 * minimum value
>> +	 */
>> +	if (intel_dp_is_uhbr(crtc_state)) {
>> +		if (crtc_state->dsc.compression_enable &&
>> +		    crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 &&
>> +		    crtc_state->pipe_bpp == 18)
> The bspec page describes this format as YUV420 at 6 bpp. Not sure how
> that would align with pipe_bpp == 18 (which is 6 _bpc_). Bspec could
> also refer to the compressed bpp, however the driver's minimum
> compressed bpp is 8. Could you clarify which bpp bspec refers to?

Here since the check if for DSC, its compressed bpp and even though 
driver's minimum bpc is 8 as per the calculations for bpc 6 min_hblank 
should be 2.

Thanks and Regards,
Arun R Murthy
-------------------

>
>> +			min_hblank = min(2, min_hblank);
>> +		else
>> +			min_hblank = min(3, min_hblank);
>> +	} else {
>> +		min_hblank = min(10, min_hblank);
>> +	}
>> +
>>   	crtc_state->min_hblank = min_hblank;
>>   
>>   	return 0;
>>
>> ---
>> base-commit: da56936fad6f5e1d5f0cef8b50277bfb071eefe7
>> change-id: 20250624-min_hblank-8af8d2626ff8
>>
>> Best regards,
>> -- 
>> Arun R Murthy <arun.r.murthy@intel.com>
>>