linux-kernel - Re: [PATCH v1] PCI: brcmstb: Fix regression regarding missing PCIe linkup

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Message-ID: <20220527232757.GA515159@bhelgaas>
Date:   Fri, 27 May 2022 18:27:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jim Quinlan <jim2101024@...il.com>
Cc:     linux-pci <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        James Dutton <james.dutton@...il.com>,
        Cyril Brulebois <kibi@...ian.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v1] PCI: brcmstb: Fix regression regarding missing PCIe
 linkup

On Wed, May 25, 2022 at 04:57:39PM -0500, Bjorn Helgaas wrote:
> On Tue, May 24, 2022 at 12:54:48PM -0400, Jim Quinlan wrote:
> > On Mon, May 23, 2022 at 6:10 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > On Sat, May 21, 2022 at 02:51:42PM -0400, Jim Quinlan wrote:
> > > > On Sat, May 21,
> > > > 2CONFIG_INITRAMFS_SOURCE="/work3/jq921458/cpio/54-arm64-rootfs.cpio022
> > > > at 12:43 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > > > On Wed, May 18, 2022 at 03:42:11PM -0400, Jim Quinlan wrote:
> > > > > > commit 93e41f3fca3d ("PCI: brcmstb: Add control of subdevice
> > > > > > voltage regulators")
> > > > > >
> > > > > > introduced a regression on the PCIe RPi4 Compute Module.  If the
> > > > > > PCIe endpoint node described in [2] was missing, no linkup would
> > > > > > be attempted, and subsequent accesses would cause a panic
> > > > > > because this particular PCIe HW causes a CPU abort on illegal
> > > > > > accesses (instead of returning 0xffffffff).
> > > > > >
> > > > > > We fix this by allowing the DT endpoint subnode to be missing.
> > > > > > This is important for platforms like the CM4 which have a
> > > > > > standard PCIe socket and the endpoint device is unknown.
> 
> > > But above you say it's the *endpoint* node that doesn't exist.  The
> > > existing code looks like it's checking for the *bridge* node
> > > (bus->dev->of_node).  We haven't even enumerated the devices on the
> > > child bus, so we don't know about them at this point.
> >
> > You are absolutely correct and I must change the commit message
> > to say the "root port DT node".   I'm sorry; this mistake likely did not
> > help you understand the fix. :-(
> 
> Great, that will help me out!  I think including the relevant DT
> snippet would also make it more concrete and might conceivably be
> helpful to somebody working around it on a kernel without the fix.

Where are we at with this?  Linus just merged my pull request, and I'd
really like to get this resolved before -rc1 (expected June 5 or so),
which means I'd like to ask him to pull the fix early next week.

The alternative is to ask him to pull these reverts, which have
actually been in -next since May 11:

  4246970a3bcb ("Revert "PCI: brcmstb: Split brcm_pcie_setup() into two funcs"")
  f35b19f02e01 ("Revert "PCI: brcmstb: Add mechanism to turn on subdev regulators"")
  ae65b283d7a4 ("Revert "PCI: brcmstb: Add control of subdevice voltage regulators"")
  d938b26e9b14 ("Revert "PCI: brcmstb: Do not turn off WOL regulators on suspend"")

Bjorn