linux-kernel - Re: [REGRESSION] [Bug 216859] New: PCI bridge to bus boot hang at enumeration

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Date:   Wed, 1 Feb 2023 16:30:32 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Krzysztof Wilczyński <kw@...ux.com>,
        alsa-devel@...a-project.org, regressions@...ts.linux.dev,
        Antonino Daplas <adaplas@...il.com>,
        Takashi Iwai <tiwai@...e.de>, linux-pci@...r.kernel.org,
        Helge Deller <deller@....de>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Javier Martinez Canillas <javierm@...hat.com>,
        linux-fbdev@...r.kernel.org,
        "Zeno R.R. Davatz" <zdavatz@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [REGRESSION] [Bug 216859] New: PCI bridge to bus boot hang at
 enumeration

[+cc Geert]

On Thu, Jan 26, 2023 at 06:11:24AM -0600, Bjorn Helgaas wrote:
> On Thu, Jan 12, 2023 at 02:08:19PM -0600, Bjorn Helgaas wrote:
> > On Wed, Dec 28, 2022 at 06:02:48AM -0600, Bjorn Helgaas wrote:
> > > On Wed, Dec 28, 2022 at 08:37:52AM +0000, bugzilla-daemon@...nel.org wrote:
> > > > https://bugzilla.kernel.org/show_bug.cgi?id=216859
> > > 
> > > >            Summary: PCI bridge to bus boot hang at enumeration
> > > >     Kernel Version: 6.1-rc1
> > > > ...
> > > 
> > > > With Kernel 6.1-rc1 the enumeration process stopped working for me,
> > > > see attachments.
> > > > 
> > > > The enumeration works fine with Kernel 6.0 and below.
> > > > 
> > > > Same problem still exists with v6.1. and v6.2.-rc1
> 
> This is a regression between v6.0 and v6.1-rc1.  Console output during
> boot freezes after nvidiafb deactivates the VGA console.
> 
> It was a lot of work for Zeno, but we finally isolated this console
> hang to 145eed48de27 ("fbdev: Remove conflicting devices on PCI bus").
> 
> The system actually does continue to boot and is accessible via ssh, 
> but the console appears hung, at least for output.  More details in
> the bugzilla starting at
> https://bugzilla.kernel.org/show_bug.cgi?id=216859#c47 .

145eed48de27 ("fbdev: Remove conflicting devices on PCI bus") doesn't
say what the benefit is, or what would break if we reverted it.

Does anybody have any clues?  It would be nice to resolve this
regression before v6.2, which will probably be released 2/12 or 2/19.

Bjorn