Re: [PATCH v1 27/27] drm/panthor: Release GPU access immediately for out-of-band grants

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] drm/panthor: AW state machine wedges in STOPPED_IDLE on ENOSPC
--

commit fc59dcd4da161e6f76c5425461851d01153db172
Author: Karunika Choo <karunika.choo@arm.com>

    drm/panthor: Release GPU access immediately for out-of-band grants

This commit modifies the window-opened IRQ handler to immediately release
the GPU access when a late grant arrives for a request that has already
timed out and returned to the READY state.

> diff --git a/drivers/gpu/drm/panthor/panthor_aw.c b/drivers/gpu/drm/panthor/panthor_aw.c
> index 7ef13db4acf50..27787c0b2f3a2 100644
> --- a/drivers/gpu/drm/panthor/panthor_aw.c
> +++ b/drivers/gpu/drm/panthor/panthor_aw.c
[ ... ]
> @@ -282,8 +282,13 @@ static void panthor_aw_handle_window_opened(struct panthor_aw *aw)
>  		return;
>  
>  	/* Window opened due to GPU_REQUEST */
> -	panthor_aw_state_try_set(aw, PANTHOR_AW_STATE_GPU_REQUEST,
> -				     PANTHOR_AW_STATE_GPU_GRANTED);
> +	if (panthor_aw_state_try_set(aw, PANTHOR_AW_STATE_GPU_REQUEST,
> +				     PANTHOR_AW_STATE_GPU_GRANTED))
> +		return;
> +
> +	if (panthor_aw_state_try_set(aw, PANTHOR_AW_STATE_READY,
> +				     PANTHOR_AW_STATE_STOPPED_IDLE))
> +		panthor_aw_send_msg(aw, VM_ARB_GPU_STOPPED);

[Severity: High]
If panthor_aw_send_msg() drops the message due to the 4-entry message FIFO
being full (-ENOSPC), does the state machine become permanently wedged in
PANTHOR_AW_STATE_STOPPED_IDLE?

Looking at panthor_aw_send_msg(), if the send FIFO is full, it returns
-ENOSPC and simply logs an error without retrying.

Because this runs in the atomic context of panthor_aw_irq_raw_hander(), it
lacks the wait-and-revert timeout fallback that thread-context callers use.
Since the state was already transitioned to PANTHOR_AW_STATE_STOPPED_IDLE
before the message was sent, dropping the message means the hardware is never
told to stop and the software state never reverts to PANTHOR_AW_STATE_READY.
This could cause all future GPU requests to timeout indefinitely under heavy
GPU load.

>  }
>  
>  static irqreturn_t panthor_aw_irq_raw_hander(int irq, void *data)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260922204535.2850094-1-karunika.choo@arm.com?part=27