[PATCH v2] drm/xe/client: Check return value of xe_force_wake_get

[Nirmoy Das]

On 6/3/2024 11:07 AM, Ghimiray, Himal Prasad wrote:
>
> On 03-06-2024 14:01, Nirmoy Das wrote:
>> xe_force_wake_get() can return error so check it's return value
>> before reading gpu_timestamp value.
>>
>> v2: set HWE to NULL instead of setting timestamp to 0(Lucas)
>>      Add a warn on for xe_force_wake_put(Himal)
>>
>> Fixes: 188ced1e0ff8 ("drm/xe/client: Print runtime to fdinfo")
>> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray at intel.com>
>> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_drm_client.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_drm_client.c 
>> b/drivers/gpu/drm/xe/xe_drm_client.c
>> index 4a19b771e3a0..4bdb909eabfc 100644
>> --- a/drivers/gpu/drm/xe/xe_drm_client.c
>> +++ b/drivers/gpu/drm/xe/xe_drm_client.c
>> @@ -264,9 +264,13 @@ static void show_run_ticks(struct drm_printer 
>> *p, struct drm_file *file)
>>           if (!hwe)
>>               continue;
>>   -        xe_force_wake_get(gt_to_fw(gt), XE_FW_GT);
>> +        if (xe_force_wake_get(gt_to_fw(gt), XE_FW_GT)) {
>
> Since xe_force_wake_get will increase the ref count irrespective of 
> acknowledgment from forcewake ack register fails or succeeds.

General pattern is to skip xe_force_wake_put() though at some places we 
do call xe_force_wake_put() when the caller is unabortable.

I don't know the exact reason but I  guess failure to wake a domain is 
serious enough so we want to  keep already woken domains  in wake state 
for system stability.


Regards,

Nirmoy


>
> It is required to decrement the ref count taken by xe_force_wake_get 
> by calling xe_force_wake_put before break.
>
> something like :
>
> if (xe_force_wake_get(gt_to_fw(gt), XE_FW_GT))
>
> hwe = NULL;
>
> else
>
> gpu_timestamp = xe_hw_engine_read_timestamp(hwe);
>
> XE_WARN_ON(xe_force_wake_put(gt_to_fw(gt), XE_FW_GT));
>
>
>> +            hwe = NULL;
>> +            break;
>> +        }
>> +
>>           gpu_timestamp = xe_hw_engine_read_timestamp(hwe);
>> -        xe_force_wake_put(gt_to_fw(gt), XE_FW_GT);
>> +        XE_WARN_ON(xe_force_wake_put(gt_to_fw(gt), XE_FW_GT));
>>           break;
>>       }