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

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Message-ID: <20251009134544.4502df0d@fedora>
Date: Thu, 9 Oct 2025 13:45:44 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Steven Price <steven.price@....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 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.