linux-kernel - Re: [PATCH] drm/panthor: Fix NULL pointer dereference on panthor_fw

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Message-ID: <20251216113949.3d737b77@fedora>
Date: Tue, 16 Dec 2025 11:39:49 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Karunika Choo <karunika.choo@....com>
Cc: dri-devel@...ts.freedesktop.org, nd@....com, Steven Price
 <steven.price@....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>,
 linux-kernel@...r.kernel.org, aishwarya.tcv@....com
Subject: Re: [PATCH] drm/panthor: Fix NULL pointer dereference on
 panthor_fw_unplug

On Mon, 15 Dec 2025 20:33:12 +0000
Karunika Choo <karunika.choo@....com> wrote:

> This patch removes the MCU halt and wait for halt procedures during
> panthor_fw_unplug() as the MCU can be in a variety of states or the FW
> may not even be loaded/initialized at all, the latter of which can lead
> to a NULL pointer dereference.
> 
> It should be safe on unplug to just disable the MCU without waiting for
> it to halt as it may not be able to.
> 
> Fixes: 514072549865 ("drm/panthor: Support GLB_REQ.STATE field for Mali-G1 GPUs")
> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Karunika Choo <karunika.choo@....com>

Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_fw.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> index 4beaa589ba66..a64ec8756bed 100644
> --- a/drivers/gpu/drm/panthor/panthor_fw.c
> +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> @@ -1261,10 +1261,6 @@ void panthor_fw_unplug(struct panthor_device *ptdev)
>  		if (ptdev->fw->irq.irq)
>  			panthor_job_irq_suspend(&ptdev->fw->irq);
>  
> -		panthor_fw_halt_mcu(ptdev);
> -		if (!panthor_fw_wait_mcu_halted(ptdev))
> -			drm_warn(&ptdev->base, "Failed to halt MCU on unplug");
> -
>  		panthor_fw_stop(ptdev);
>  	}
>