Re: [PATCH] drm/i915/mst: limit DP MST ESI service loop

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

On Wed, 01 Jul 2026, Imre Deak <imre.deak@intel.com> wrote:
> On Thu, Jun 25, 2026 at 05:22:04PM +0300, Jani Nikula wrote:
>> The loop in intel_dp_check_mst_status() keeps servicing interrupts
>> originating from the sink without bound. Add an upper bound to the new
>> interrupts occurring during interrupt processing to not get stuck on
>> potentially stuck sink devices. Use arbitrary 32 tries to clear incoming
>> interrupts in one go.
>> 
>> Discovered using AI-assisted static analysis confirmed by Intel Product
>> Security.
>> 
>> Note: The condition likely pre-dates the commit in the Fixes: tag, but
>> this is about as far back as a backport has any chance of
>> succeeding. Before that, the retry had a goto.
>> 
>> Reported-by: Martin Hodo <martin.hodo@intel.com>
>> Fixes: 3c0ec2c2d594 ("drm/i915: Flatten intel_dp_check_mst_status() a bit")
>> Cc: <stable@vger.kernel.org> # v5.8+
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Imre Deak <imre.deak@intel.com>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>
> Reviewed-by: Imre Deak <imre.deak@intel.com>

Thanks, pushed to din.

BR,
Jani.

>
>> ---
>>  drivers/gpu/drm/i915/display/intel_dp.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 6e3fa6662cbe..ade7e51e7590 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -5590,8 +5590,9 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>>  	struct intel_display *display = to_intel_display(intel_dp);
>>  	bool force_retrain = intel_dp_link_training_get_force_retrain(intel_dp->link.training);
>>  	bool reprobe_needed = false;
>> +	int tries = 33;
>>  
>> -	for (;;) {
>> +	while (--tries) {
>>  		u8 esi[4] = {};
>>  		u8 ack[4] = {};
>>  		bool new_irqs;
>> @@ -5634,6 +5635,11 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
>>  			break;
>>  	}
>>  
>> +	if (!tries) {
>> +		drm_dbg_kms(display->drm, "DPRX ESI not clearing, device may be stuck\n");
>> +		reprobe_needed = true;
>> +	}
>> +
>>  	return !reprobe_needed;
>>  }
>>  
>> -- 
>> 2.47.3
>> 

-- 
Jani Nikula, Intel