linux-kernel - Re: [PATCH v2] PCI: Coalesce contiguous regions for host bridges

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Message-ID: <20210709234314.GA1181719@bjorn-Precision-5520>
Date:   Fri, 9 Jul 2021 18:43:14 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>, bhelgaas@...gle.com,
        "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: Coalesce contiguous regions for host bridges

On Fri, Jul 09, 2021 at 04:15:29PM -0700, Guenter Roeck wrote:
> Hi,
> 
> On Thu, Apr 01, 2021 at 09:12:52PM +0800, Kai-Heng Feng wrote:
> > Built-in graphics on HP EliteDesk 805 G6 doesn't work because graphics
> > can't get the BAR it needs:
> > [    0.611504] pci_bus 0000:00: root bus resource [mem 0x10020200000-0x100303fffff window]
> > [    0.611505] pci_bus 0000:00: root bus resource [mem 0x10030400000-0x100401fffff window]
> > ...
> > [    0.638083] pci 0000:00:08.1:   bridge window [mem 0xd2000000-0xd23fffff]
> > [    0.638086] pci 0000:00:08.1:   bridge window [mem 0x10030000000-0x100401fffff 64bit pref]
> > [    0.962086] pci 0000:00:08.1: can't claim BAR 15 [mem 0x10030000000-0x100401fffff 64bit pref]: no compatible bridge window
> > [    0.962086] pci 0000:00:08.1: [mem 0x10030000000-0x100401fffff 64bit pref] clipped to [mem 0x10030000000-0x100303fffff 64bit pref]
> > [    0.962086] pci 0000:00:08.1:   bridge window [mem 0x10030000000-0x100303fffff 64bit pref]
> > [    0.962086] pci 0000:07:00.0: can't claim BAR 0 [mem 0x10030000000-0x1003fffffff 64bit pref]: no compatible bridge window
> > [    0.962086] pci 0000:07:00.0: can't claim BAR 2 [mem 0x10040000000-0x100401fffff 64bit pref]: no compatible bridge window
> > 
> > However, the root bus has two contiguous regions that can contain the
> > child resource requested.
> > 
> > Bjorn Helgaas pointed out that we can simply coalesce contiguous regions
> > for host bridges, since host bridge don't have _SRS. So do that
> > accordingly to make child resource can be contained. This change makes
> > the graphics works on the system in question.
> > 
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212013
> > Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> 
> With this patch in place, I can no longer boot the ppc:sam460ex
> qemu emulation from nvme. I see the following boot error:
> 
> nvme nvme0: Device not ready; aborting initialisation, CSTS=0x0
> nvme nvme0: Removing after probe failure status: -19

Thanks for the report and bisection!

I'll try to get this reverted before v5.14-rc1.

Bjorn