linux-kernel - Re: [PATCH] drm/mxsfb: fix missing rollback on failure in mxsfb

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Message-ID: <CABGWkvqtj+05sdOuXg1WO99VNm9qdFgcYWEGuUPPZPoHZa6Dew@mail.gmail.com>
Date: Thu, 13 Mar 2025 21:43:24 +0100
From: Dario Binacchi <dario.binacchi@...rulasolutions.com>
To: Thomas Zimmermann <tzimmermann@...e.de>
Cc: Luca Ceresoli <luca.ceresoli@...tlin.com>, Marek Vasut <marex@...x.de>, 
	Stefan Agner <stefan@...er.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, 
	Michael Trimarchi <michael@...rulasolutions.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>, dri-devel@...ts.freedesktop.org, 
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/mxsfb: fix missing rollback on failure in mxsfb_probe()

Hi All,

On Thu, Mar 13, 2025 at 3:40 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
>
> Hi
>
> Am 13.03.25 um 15:25 schrieb Luca Ceresoli:
> > When aperture_remove_all_conflicting_devices() fails, the current code
> > returns without going through the rollback actions at the end of the
> > function, thus the actions done by drm_dev_alloc() and mxsfb_load() are not
> > undone.
> >
> > Fix by using a goto statament, as done for the previous and following error
> > conditions.
> >
> > Fixes: c8e7b185d45b ("drm/mxsfb: Remove generic DRM drivers in probe function")
> > Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > ---
> > The offending commit is not yet merged into master, and even less in a
> > released kernel, so this does not need to go through stable.
> > ---
> >   drivers/gpu/drm/mxsfb/mxsfb_drv.c | 7 ++++---
> >   1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> > index c183b1112bc4e9fe4f3b048a2b6e4c98d1d47cb3..b4273e678d26dbc3dee2014266d61470da4e8010 100644
> > --- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> > +++ b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
> > @@ -365,9 +365,10 @@ static int mxsfb_probe(struct platform_device *pdev)
> >        * located anywhere in RAM
> >        */
> >       ret = aperture_remove_all_conflicting_devices(mxsfb_driver.name);
> > -     if (ret)
> > -             return dev_err_probe(&pdev->dev, ret,
> > -                                  "can't kick out existing framebuffers\n");
> > +     if (ret) {
> > +             dev_err_probe(&pdev->dev, ret, "can't kick out existing framebuffers\n");
> > +             goto err_unload;
> > +     }
>
> I must have missed that when I reviewed the patch. But this call should
> happen much earlier. right at the top of the probe function before
> drm_dev_alloc().

I had added the call to aperture_remove_all_conflicting_devices()
after mxsfb_load() to
keep the splash screen loaded by U-Boot. So, IMHO, it would be better
to add the
goto in case of an error rather than moving
aperture_remove_all_conflicting_devices()
to the beginning of the probe function.

Thanks and regards,
Dario

> Conflicting drivers need to be kicked out before
> setting up DRM. Could you please send a patch to move the call to the
> top? No extra cleanup would be required then.
>
> Best regards
> Thomas
>
> >
> >       ret = drm_dev_register(drm, 0);
> >       if (ret)
> >
> > ---
> > base-commit: f9f087d946266bc5da7c3a17bd8fd9d01969e3cf
> > change-id: 20250313-mxsfb_probe-fix-rollback-on-error-3074b9080f34
> >
> > Best regards,
>
> --
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
>


-- 

Dario Binacchi

Senior Embedded Linux Developer

dario.binacchi@...rulasolutions.com

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