[PATCH] drm/v3d: Enable Performance Counters before clearing them

[Maíra Canal]

Hi Iago,

On 04/12/24 09:36, Iago Toral wrote:
> Reviewed-by: Iago Toral Quiroga <itoral at igalia.com>

Thanks for reviewing! Applied to misc/kernel.git (drm-misc-fixes).

Best Regards,
- Maíra

> 
> El mié, 04-12-2024 a las 09:28 -0300, Maíra Canal escribió:
>> On the Raspberry Pi 5, performance counters are not being cleared
>> when `v3d_perfmon_start()` is called, even though we write to the
>> CLR register. As a result, their values accumulate until they
>> overflow.
>>
>> The expected behavior is for performance counters to reset to zero
>> at the start of a job. When the job finishes and the perfmon is
>> stopped, the counters should accurately reflect the values for that
>> specific job.
>>
>> To ensure this behavior, the performance counters are now enabled
>> before being cleared. This allows the CLR register to function as
>> intended, zeroing the counter values when the job begins.
>>
>> Fixes: 26a4dc29b74a ("drm/v3d: Expose performance counters to
>> userspace")
>> Signed-off-by: Maíra Canal <mcanal at igalia.com>
>> ---
>>   drivers/gpu/drm/v3d/v3d_perfmon.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/v3d/v3d_perfmon.c
>> b/drivers/gpu/drm/v3d/v3d_perfmon.c
>> index b4c3708ea781..c49abb90954d 100644
>> --- a/drivers/gpu/drm/v3d/v3d_perfmon.c
>> +++ b/drivers/gpu/drm/v3d/v3d_perfmon.c
>> @@ -255,9 +255,9 @@ void v3d_perfmon_start(struct v3d_dev *v3d,
>> struct v3d_perfmon *perfmon)
>>   		V3D_CORE_WRITE(0, V3D_V4_PCTR_0_SRC_X(source),
>> channel);
>>   	}
>>   
>> +	V3D_CORE_WRITE(0, V3D_V4_PCTR_0_EN, mask);
>>   	V3D_CORE_WRITE(0, V3D_V4_PCTR_0_CLR, mask);
>>   	V3D_CORE_WRITE(0, V3D_PCTR_0_OVERFLOW, mask);
>> -	V3D_CORE_WRITE(0, V3D_V4_PCTR_0_EN, mask);
>>   
>>   	v3d->active_perfmon = perfmon;
>>   }
>