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

From: Bjorn Helgaas <helgaas@kernel.org>
To: Jim Quinlan <jim2101024@gmail.com>
Cc: linux-pci <linux-pci@vger.kernel.org>,
	"Nicolas Saenz Julienne" <nsaenz@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"James Dutton" <james.dutton@gmail.com>,
	"Cyril Brulebois" <kibi@debian.org>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
	"Jim Quinlan" <james.quinlan@broadcom.com>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE"
	<linux-rpi-kernel@lists.infradead.org>,
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	"open list" <linux-kernel@vger.kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	linux-pm@vger.kernel.org
Subject: Re: [PATCH v1] PCI: brcmstb: Fix regression regarding missing PCIe linkup
Date: Fri, 27 May 2022 18:27:57 -0500	[thread overview]
Message-ID: <20220527232757.GA515159@bhelgaas> (raw)
In-Reply-To: <20220525215739.GA275957@bhelgaas>

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@kernel.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@kernel.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