linux-kernel - Re: [PATCH] drm/panthor: Ensure MCU is disabled on suspend

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Message-ID: <d526aaed-b29d-4e19-aab4-aa735282055e@arm.com>
Date: Thu, 9 Oct 2025 11:29:14 +0100
From: Steven Price <steven.price@....com>
To: Ketil Johnsen <ketil.johnsen@....com>,
 Boris Brezillon <boris.brezillon@...labora.com>,
 Liviu Dudau <liviu.dudau@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panthor: Ensure MCU is disabled on suspend

On 08/10/2025 11:51, Ketil Johnsen wrote:
> Currently the Panthor driver needs the GPU to be powered down
> between suspend and resume. If this is not done, then the
> MCU_CONTROL register will be preserved as AUTO, which again will
> cause a premature FW boot on resume. The FW will go directly into
> fatal state in this case.
> 
> This case needs to be handled as there is no guarantee that the
> GPU will be powered down after the suspend callback on all platforms.
> 
> The fix is to call panthor_fw_stop() in "pre-reset" path to ensure
> the MCU_CONTROL register is cleared (set DISABLE). This matches
> well with the already existing call to panthor_fw_start() from the
> "post-reset" path.
> 
> Signed-off-by: Ketil Johnsen <ketil.johnsen@....com>

Reviewed-by: Steven Price <steven.price@....com>

Do we need a Fixes tag? Or is this only actually an issue on newer GPUs?

Thanks,
Steve

> ---
>  drivers/gpu/drm/panthor/panthor_fw.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> index 9bf06e55eaee..df767e82148a 100644
> --- a/drivers/gpu/drm/panthor/panthor_fw.c
> +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> @@ -1099,6 +1099,7 @@ void panthor_fw_pre_reset(struct panthor_device *ptdev, bool on_hang)
>  	}
>  
>  	panthor_job_irq_suspend(&ptdev->fw->irq);
> +	panthor_fw_stop(ptdev);
>  }
>  
>  /**