[Intel-gfx] [PATCH] drm/i915/xelpd: Calculate first_line_bpg_offset for DSC 1.1

[Tseng, William]

Thank you for the comments.  It seems the correction is for DSC 1.1 and DSC 1.2 at the same time.
Can you submit a patch for the correction?  Because the original patch is specifically for the original specification DSC 1.1.

-----Original Message-----
From: Nautiyal, Ankit K <ankit.k.nautiyal at intel.com> 
Sent: Wednesday, August 2, 2023 7:39 PM
To: Kandpal, Suraj <suraj.kandpal at intel.com>; Tseng, William <william.tseng at intel.com>; intel-gfx at lists.freedesktop.org
Cc: Heikkila, Juha-pekka <juha-pekka.heikkila at intel.com>
Subject: Re: [Intel-gfx] [PATCH] drm/i915/xelpd: Calculate first_line_bpg_offset for DSC 1.1


On 8/2/2023 4:45 PM, Kandpal, Suraj wrote:
> 1.1
>> This change is required for DSC 1.1 because the current calculation 
>> is for DSC
>> 1.2 and may get a calculated value which is not recommended by DSC 
>> 1.1, for example, the calculated value at 8bpp becomes 15, not the 
>> value of 12 recommened by DSC 1.1.
>>
>> Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
>> Cc: Juha-Pekka Heikkil <juha-pekka.heikkila at intel.com>
>> Signed-off-by: William Tseng <william.tseng at intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_vdsc.c | 17 ++++++++++++-----
>>   1 file changed, 12 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c
>> b/drivers/gpu/drm/i915/display/intel_vdsc.c
>> index bd9116d2cd76..9b350f5f8ebb 100644
>> --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
>> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
>> @@ -72,11 +72,18 @@ calculate_rc_params(struct drm_dsc_config
>> *vdsc_cfg)
>>   	int qp_bpc_modifier = (bpc - 8) * 2;
>>   	u32 res, buf_i, bpp_i;
>>
>> -	if (vdsc_cfg->slice_height >= 8)
>> -		vdsc_cfg->first_line_bpg_offset =
>> -			12 + DIV_ROUND_UP((9 * min(34, vdsc_cfg-

This seem to be incorrect as per the spec this should have been first_line_bpg_offset = 12 + floor(0.09 * MIN (34, slice_height - 8))for slice_height ≥ 8

So instead of rounding up we should have just divided.


>>> slice_height - 8)), 100);
>> -	else
>> -		vdsc_cfg->first_line_bpg_offset = 2 * (vdsc_cfg-
>>> slice_height - 1);
>> +	if (vdsc_cfg->dsc_version_minor == 2) {
> I think the check here should be for minor version 1 and move the code 
> in this block to the else block and vice versa as this 8 bpp corner 
> case is applicable only to DSC 1.1
>   
>> +		if (vdsc_cfg->slice_height >= 8)
>> +			vdsc_cfg->first_line_bpg_offset =
>> +				12 + DIV_ROUND_UP((9 * min(34, vdsc_cfg-
>>> slice_height - 8)), 100);
>> +		else
>> +			vdsc_cfg->first_line_bpg_offset = 2 * (vdsc_cfg-
>>> slice_height - 1);
>> +	} else {
>> +		if (bpp == 8)
>> +			rc->first_line_bpg_offset = 12;
>> +		else
>> +			rc->first_line_bpg_offset = 15;
>> +	}
> Add the section in DSC spec/ Cmodel from where one can verify this in 
> comments

I think this is coming from the recommended/ required value from DSC 1.1.


Regards,

Ankit

>
> Regards,
> Suraj Kandpal
>>   	/* Our hw supports only 444 modes as of today */
>>   	if (bpp >= 12)
>> --
>> 2.34.1