[PATCH] drm/i915/dp: Limit max compressed bpp to 18 when forcing DSC

[Nautiyal, Ankit K]

On 11/11/2024 12:25 PM, Srikanth V, NagaVenkata wrote:
>
>> -----Original Message-----
>> From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of Ankit
>> Nautiyal
>> Sent: Wednesday, October 30, 2024 2:11 PM
>> To: intel-gfx at lists.freedesktop.org
>> Cc: intel-xe at lists.freedesktop.org
>> Subject: [PATCH] drm/i915/dp: Limit max compressed bpp to 18 when
>> forcing DSC
>>
>> While forcing DSC when it is not actually required, the max compressed bpp
>> from the source gets picked for compression for some pipe bpps.
>> Apparently, when DSC is not required, forcing DSC to the maximum
>> compressed bpp seems to cause underruns.
>>
>> To avoid this, limit the max compressed bpp to 18 while forcing DSC. This
>> value works across platforms with different pipe bpps and prevents
>> underruns.
>>
>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> Looks good to me.
> Reviewed-by: Naga Venkata Srikanth V <nagavenkata.srikanth.v at intel.com>

Thank you Srikanth for the review. This is now pushed to drm-intel-next.

Regards,

Ankit

>
>> ---
>>   drivers/gpu/drm/i915/display/intel_dp.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
>> b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 28fa5e2d0c33..0ce29cefaa13 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -2021,6 +2021,15 @@ static int dsc_src_max_compressed_bpp(struct
>> intel_dp *intel_dp)  {
>>   	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>>
>> +	/*
>> +	 * Forcing DSC and using the platform's max compressed bpp is seen
>> to cause
>> +	 * underruns. Since DSC isn't needed in these cases, limit the
>> +	 * max compressed bpp to 18, which is a safe value across platforms
>> with different
>> +	 * pipe bpps.
>> +	 */
>> +	if (intel_dp->force_dsc_en)
>> +		return 18;
>> +
>>   	/*
>>   	 * Max Compressed bpp for Gen 13+ is 27bpp.
>>   	 * For earlier platform is 23bpp. (Bspec:49259).
>> --
>> 2.45.2