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

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Message-ID: <f3b04a09-561f-4eb6-9730-7084e5b9697b@arm.com>
Date: Thu, 9 Oct 2025 13:51:19 +0100
From: Steven Price <steven.price@....com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Ketil Johnsen <ketil.johnsen@....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>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panthor: Ensure MCU is disabled on suspend

On 09/10/2025 12:45, Boris Brezillon wrote:
> On Thu, 9 Oct 2025 11:29:14 +0100
> Steven Price <steven.price@....com> wrote:
> 
>> 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?
> 
> I think it'd be good to have a Fixes tag, if it's known to be the right
> thing to do after a HALT, even if it's not needed on the GPUs currently
> supported by this driver.

Yeah, at the very least it won't do any harm. I'll add a:

Fixes: 2718d91816ee ("drm/panthor: Add the FW logical block")

And merge this to drm-misc-fixes.

Thanks,
Steve