[PATCH 1/3] drm/amd/display: Fix refactored DSC cap calculation

[Alex Hung]

This patch may be related and conflict to 
https://www.mail-archive.com/amd-gfx@lists.freedesktop.org/msg125873.html

amd-staging-drm-next should include the above patch but it is not 
updated for 2 weeks, so let's wait for ASDN to be updated.


On 7/24/25 16:32, Rodrigo Siqueira wrote:
> On 010/22, Timur Kristóf wrote:
>> After refactoring the DSC capability calculation, the
>> get_min_slice_count_for_odm could crash on some GPUs due to a
>> division by zero when max_total_throughput_mps was zero.
>> As a result, DC was broken when connecting a GPU that doesn't
>> support DSC to a monitor that supports DSC.
>> Tested on Oland (DCE 6) and Fiji (DCE 10).
>>
>> This commit fixes it by returning zero instead.
>>
>> Fixes: 4909b8b3846c ("drm/amd/display: Refactor DSC cap calculations")
>> Signed-off-by: Timur Kristóf <timur.kristof at gmail.com>
>> ---
>>   drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c | 17 +++++++++--------
>>   1 file changed, 9 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
>> index a454d16e6586..4169ece9c535 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
>> @@ -642,14 +642,15 @@ static unsigned int get_min_slice_count_for_odm(
>>   	unsigned int max_dispclk_khz;
>>   
>>   	/* get max pixel rate and combine caps */
>> -	max_dispclk_khz = dsc_enc_caps->max_total_throughput_mps * 1000;
>> -	if (dsc && dsc->ctx->dc) {
>> -		if (dsc->ctx->dc->clk_mgr &&
>> -			dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz) {
>> -			/* dispclk is available */
>> -			max_dispclk_khz = dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz(dsc->ctx->dc->clk_mgr, CLK_TYPE_DISPCLK);
>> -		}
>> -	}
>> +	if (dsc && dsc->ctx->dc && dsc->ctx->dc->clk_mgr &&
>> +		dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz)
>> +		max_dispclk_khz =
>> +			dsc->ctx->dc->clk_mgr->funcs->get_max_clock_khz(
>> +				dsc->ctx->dc->clk_mgr, CLK_TYPE_DISPCLK);
>> +	else if (dsc_enc_caps->max_total_throughput_mps)
>> +		max_dispclk_khz = dsc_enc_caps->max_total_throughput_mps * 1000;
>> +	else
>> +		return 0;
>>   
>>   	/* consider minimum odm slices required due to
>>   	 * 1) display pipe throughput (dispclk)
>> -- 
>> 2.50.1
>>
> 
> This patch lgtm.
> 
> Reviewed-by: Rodrigo Siqueira <siqueira at igalia.com>
> 
> I added other display folks to this patch.
> 
> I'm not sure if the original modification (4909b8b3846c) is already in
> the stable kernel; if so, it could be a good idea to send this fix to
> the stable kernel as well.
> 
> Thanks
>