Re: [PATCH v2 5/5] drm/msm/dpu: rate limit snapshot capture for mmu faults

[Jessica Zhang <quic_jesszhan@quicinc.com>]

On 12/18/2024 3:20 AM, Dmitry Baryshkov wrote:
> On Tue, Dec 17, 2024 at 04:27:57PM -0800, Jessica Zhang wrote:
>> From: Abhinav Kumar <quic_abhinavk@quicinc.com>
>>
>> There is no recovery mechanism in place yet to recover from mmu
>> faults for DPU. We can only prevent the faults by making sure there
>> is no misconfiguration.
>>
>> Rate-limit the snapshot capture for mmu faults to once per
>> msm_atomic_commit_tail() as that should be sufficient to capture
>> the snapshot for debugging otherwise there will be a lot of DPU
>> snapshots getting captured for the same fault which is redundant
>> and also might affect capturing even one snapshot accurately.
>>
>> Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
>> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
>> ---
>>   drivers/gpu/drm/msm/msm_atomic.c | 2 ++
>>   drivers/gpu/drm/msm/msm_kms.c    | 5 ++++-
>>   drivers/gpu/drm/msm/msm_kms.h    | 3 +++
>>   3 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
>> index 9c45d641b5212c11078ab38c13a519663d85e10a..9ad7eeb14d4336abd9d8a8eb1382bdddce80508a 100644
>> --- a/drivers/gpu/drm/msm/msm_atomic.c
>> +++ b/drivers/gpu/drm/msm/msm_atomic.c
>> @@ -228,6 +228,8 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
>>   	if (kms->funcs->prepare_commit)
>>   		kms->funcs->prepare_commit(kms, state);
>>   
>> +	kms->fault_snapshot_capture = 0;
>> +
> 
> - Please move it before the prepare_commit().
> - You are accessing the same variable from different threads / cores.
>    There should be some kind of a sync barrier.

Hi Dmitry,

Ack, will add a lock for the snapshot capture counter.

Thanks,

Jessica Zhang

> 
>>   	/*
>>   	 * Push atomic updates down to hardware:
>>   	 */
>> diff --git a/drivers/gpu/drm/msm/msm_kms.c b/drivers/gpu/drm/msm/msm_kms.c
>> index 78830e446355f77154fa21a5d107635bc88ba3ed..3327caf396d4fc905dc127f09515559c12666dc8 100644
>> --- a/drivers/gpu/drm/msm/msm_kms.c
>> +++ b/drivers/gpu/drm/msm/msm_kms.c
>> @@ -168,7 +168,10 @@ static int msm_kms_fault_handler(void *arg, unsigned long iova, int flags, void
>>   {
>>   	struct msm_kms *kms = arg;
>>   
>> -	msm_disp_snapshot_state(kms->dev);
>> +	if (!kms->fault_snapshot_capture) {
>> +		msm_disp_snapshot_state(kms->dev);
>> +		kms->fault_snapshot_capture++;
>> +	}
>>   
>>   	return -ENOSYS;
>>   }
>> diff --git a/drivers/gpu/drm/msm/msm_kms.h b/drivers/gpu/drm/msm/msm_kms.h
>> index e60162744c669773b6e5aef824a173647626ab4e..3ac089e26e14b824567f3cd2c62f82a1b9ea9878 100644
>> --- a/drivers/gpu/drm/msm/msm_kms.h
>> +++ b/drivers/gpu/drm/msm/msm_kms.h
>> @@ -128,6 +128,9 @@ struct msm_kms {
>>   	int irq;
>>   	bool irq_requested;
>>   
>> +	/* rate limit the snapshot capture to once per attach */
>> +	int fault_snapshot_capture;
>> +
>>   	/* mapper-id used to request GEM buffer mapped for scanout: */
>>   	struct msm_gem_address_space *aspace;
>>   
>>
>> -- 
>> 2.34.1
>>
> 
> -- 
> With best wishes
> Dmitry