Re: [PATCH v12 10/15] drm/panfrost: Add debugfs knob for manually triggering a GPU reset

[Steven Price]

On 06/10/2026 14:38, Adrián Larumbe wrote:
> On 2026-10-02 16:10:43+01:00, Steven Price wrote:
>> On 29/09/2026 04:44, Adrián Larumbe wrote:
>>
>>> This will be of great help when testing potential races between the GPU
>>> reset sequence and other parts of the code accessing HW registers.
>>>
>>> We must also disable the reset work item rather than simply cancelling
>>> it, to prevent the knob from triggering another reset when the device
>>> is being removed.
>>>
>>> Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
>>> Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
>>> ---
>>>  drivers/gpu/drm/panfrost/panfrost_device.c | 42 ++++++++++++++++++++++++++++++
>>>  drivers/gpu/drm/panfrost/panfrost_job.c    |  2 +-
>>>  2 files changed, 43 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
>>> index 09a5752a3f40..94d2de341838 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
>>> @@ -2,6 +2,7 @@
>>>  /* Copyright 2018 Marty E. Plummer <hanetzer@xxxxxxxxxxxxx> */
>>>  /* Copyright 2019 Linaro, Ltd, Rob Herring <robh@xxxxxxxxxx> */
>>>  
>>> +#include <linux/debugfs.h>
>>>  #include <linux/clk.h>
>>>  #include <linux/reset.h>
>>>  #include <linux/platform_device.h>
>>> @@ -595,9 +596,50 @@ EXPORT_GPL_DEV_PM_OPS(panfrost_pm_ops) = {
>>>  };
>>>  
>>>  #ifdef CONFIG_DEBUG_FS
>>> +static int reset_get(void *data, u64 *val)
>>> +{
>>> +	struct panfrost_device *pfdev =
>>> +		container_of(data, struct panfrost_device, base);
>>> +
>>> +	*val = atomic_read(&pfdev->reset.pending);
>>> +	return 0;
>>> +}
>>> +
>>> +static int reset_set(void *data, u64 val)
>>> +{
>>> +	struct panfrost_device *pfdev =
>>> +		container_of(data, struct panfrost_device, base);
>>> +	int ret = pm_runtime_get_if_active(pfdev->base.dev);
>>> +
>>> +	if (!ret)
>>> +		return 0;
>>> +
>>> +	panfrost_device_schedule_reset(pfdev);
>>> +	flush_work(&pfdev->reset.work);
>>> +
>>> +	/* ret < 0 means runtime PM for the device is disabled, so we
>>> +	 * only need to return the PM reference in the opposite case
>>> +	 */
>>> +	if (ret > 0)
>>> +		pm_runtime_put(pfdev->base.dev);
>>> +
>>> +	return 0;
>>> +}
>>
>> NIT: If this wasn't debugfs I'd be complaining that you're ignoring
>> 'val' and so this isn't very extensible. But hey, it's debugfs... so:
>>
>> Reviewed-by: Steven Price <steven.price@xxxxxxx>
> 
> I looked into the available debugfs attribute definition macros and none of them provide
> a wrapper that avoid passing the input value when the attribute is to be understood as
> an action rather than a device property. My understanding is that because debugfs doesn't
> become part of the device's uAPI, we can do pretty much whatever we want with it.
> However, on a second thought, maybe in the future we'll want to extend the knob so that
> it performs resets in different ways, and would want to keep backwards compatibility with
> UM binaries that expect certain input values to stand for specific actions.
> 
> I'll change it so that all value other than '1' are returned with -EINVAL.

That would be my preference, but like you say this is debugfs so we
don't consider it part of uAPI. Mostly it seems a bit odd that you could
read the value, get 0 (i.e. no reset), write it back and that would
trigger a reset. But equally this isn't the sort of file which you'd
expect a read-modify-write operation to work on, so it's not a big deal.

Thanks,
Steve