linux-kernel - Re: Kconfig CONFIG_FB dependency regression

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Date:   Wed, 2 Feb 2022 08:46:00 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     Fabio Estevam <festevam@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        John Youn <John.Youn@...opsys.com>,
        Bing Yuan <Bing.Yuan@...opsys.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Kconfig CONFIG_FB dependency regression

On Wed, Feb 2, 2022 at 1:14 AM Thinh Nguyen <Thinh.Nguyen@...opsys.com> wrote:
> Fabio Estevam wrote:
> > On Tue, Feb 1, 2022 at 8:06 PM Randy Dunlap <rdunlap@...radead.org> wrote:
> >>
> >> On 2/1/22 15:01, Thinh Nguyen wrote:
> >>> Hi,
> >>>
> >>> One of our test setups is unable to boot (stuck at initramfs). Git
> >>> bisection points to the commit below:
> >>>
> >>> f611b1e7624c ("drm: Avoid circular dependencies for CONFIG_FB")
> >>>
> >>> Reverting this patch resolves the issue. This issue persists in mainline
> >>> also. Unfortunately there isn't any meaningful log. Hopefully someone
> >>> can give some insight as to what could be the issue and revert/fix this
> >>> issue.
> >>
> >> Hi,
> >> Did you enable DRM_FBDEV_EMULATION?
>
> I did not enable it.
>
> >> Please provide the failing .config file.
> >
> > Does selecting CONFIG_FB=y help?
> >
>
> On the config that has the issue, this isn't set. After reverting the
> commit above, this was set. Maybe this is what's needed? I need to test it.

CONFIG_FB should not normally be needed for booting, so unless
you have a graphical application in your initramfs that requires the /dev/fb0
device to work, it is not supposed to make a difference.

Are there any other differences in your .config before and after the patch?
It's possible that you use some other driver that in turn depends on
CONFIG_FB. Does your machine have any graphical output device?
If yes, which driver do you use?

You may also want to make sure that you have 9d6366e743f3 ("drm:
fb_helper: improve CONFIG_FB dependency") in your kernel, which
fixes a minor problem with my original patch.

         Arnd