linux-kernel - Re: [PATCH 1/2] fbdev/offb: Update expected device name

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Message-ID: <20230615211924.cf2qs52cfaf7m3f7@debamax.com>
Date:   Thu, 15 Jun 2023 23:19:24 +0200
From:   Cyril Brulebois <cyril@...amax.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Michal Suchánek <msuchanek@...e.de>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Linux regressions mailing list <regressions@...ts.linux.dev>,
        Salvatore Bonaccorso <carnil@...ian.org>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] fbdev/offb: Update expected device name

Hi Rob,

Rob Herring <robh@...nel.org> (2023-06-15):
> On Thu, Jun 15, 2023 at 03:21:07PM +0200, Michal Suchánek wrote:
> > At the time this was proposed it was said that "of-display", is wrong,
> > and that "of-display.0" must be used for the first device instead, and
> > if something breaks an alias can be provided.
> > 
> > So how does one provide an alias so that offb can find "of-display.0"
> > as "of-display"?
> 
> I'm not aware of any way. There isn't because device names and paths are 
> not considered ABI. There are mechanisms for getting stable class device 
> indices (e.g. i2c0, mmcblk0, fb0, fb1, etc.) though not implemented for 
> fbN (and please don't add it). 
> 
> In any case, this should be an easy fix. Though if "linux,opened" or 
> "linux,boot-display" is not set, then you'd still get "of-display.0":
> 
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 78ae84187449..e46482cef9c7 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -553,7 +553,7 @@ static int __init of_platform_default_populate_init(void)
>                         if (!of_get_property(node, "linux,opened", NULL) ||
>                             !of_get_property(node, "linux,boot-display", NULL))
>                                 continue;
> -                       dev = of_platform_device_create(node, "of-display.0", NULL);
> +                       dev = of_platform_device_create(node, "of-display", NULL);
>                         of_node_put(node);
>                         if (WARN_ON(!dev))
>                                 return -ENOMEM;

I've just replaced my clueless workaround with this patch on top of the
kernel found in Debian 12 (Bookworm), i.e. 6.1.27 at this point, and it
indeed fixes the black screen problem in the installer's context.

I didn't run a full installation to check whether this kernel is also fine
after rebooting into the installed system, but as far as I understood for
the original bug report[1], it wasn't affected in the first place.

 1. https://bugs.debian.org/1033058

Will somebody else pick up the torch from here, and submit that for
inclusion in master? Or should I re-submit the above patch on my own?

I see my Debian colleagues have already pushed an updated v6.4-rc6 in
experimental, so it should be rather easy to combine checking latest
master with the distribution's packaging. Once that's done, I'm quite
familiar with building an updated installer image on top of it…


Thanks,
-- 
Cyril Brulebois -- Debian Consultant @ DEBAMAX -- https://debamax.com/

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