Re: [PATCH] drm/i915/dp: Fix potential infinite loop in 128b/132b SST

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 04 Feb 2025, Imre Deak <imre.deak@intel.com> wrote:
> On Tue, Feb 04, 2025 at 05:49:25PM +0200, Jani Nikula wrote:
>> Passing 0 as the step only works when there are other reasons to break
>> out of the BPP loop in intel_dp_mtp_tu_compute_config(). Otherwise, an
>> infinite loop might occur. Fix it by explicitly checking for 0 step.
>> 
>> Fixes: ef0a0757bbea ("drm/i915/dp: compute config for 128b/132b SST w/o DSC")
>> Reported-by: Imre Deak <imre.deak@intel.com>
>> Closes: https://lore.kernel.org/r/Z6I0knh2Kt5T0JrT@ideak-desk.fi.intel.com
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>
> Reviewed-by: Imre Deak <imre.deak@intel.com>

Pushed to din, thanks for the review!

>
>> ---
>> 
>> Note: This needs a backport with (!step) for -rc1.
>> ---
>>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> index 95abc6ea85eb..1587be5cd0a7 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> @@ -353,6 +353,10 @@ int intel_dp_mtp_tu_compute_config(struct intel_dp *intel_dp,
>>  
>>  			break;
>>  		}
>> +
>> +		/* Allow using zero step to indicate one try */
>> +		if (!bpp_step_x16)
>> +			break;
>>  	}
>>  
>>  	if (slots < 0) {
>> -- 
>> 2.39.5
>> 

-- 
Jani Nikula, Intel