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

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Date:   Wed, 18 May 2022 15:42:11 -0400
From:   Jim Quinlan <jim2101024@...il.com>
To:     linux-pci@...r.kernel.org,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, james.dutton@...il.com,
        kibi@...ian.org, bcm-kernel-feedback-list@...adcom.com,
        jim2101024@...il.com, james.quinlan@...adcom.com
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-rpi-kernel@...ts.infradead.org (moderated list:BROADCOM
        BCM2711/BCM2835 ARM ARCHITECTURE),
        linux-arm-kernel@...ts.infradead.org (moderated list:BROADCOM
        BCM2711/BCM2835 ARM ARCHITECTURE),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v1] PCI: brcmstb: Fix regression regarding missing PCIe linkup

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.

Please do not accept this commit until someone with a CM4 has tested
this solution; I have only emulated the problem and fix on different
platform.

Note that a bisection identified

commit 830aa6f29f07 ("PCI: brcmstb: Split brcm_pcie_setup() into two funcs")

as the first failing commit.  This commit is a regression, but is unrelated
and was fixed by a subsequent commit in the original patchset.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=215925
[2] Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml

Fixes: 93e41f3fca3d ("PCI: brcmstb: Add control of subdevice voltage regulators")
Fixes: 830aa6f29f07 ("PCI: brcmstb: Split brcm_pcie_setup() into two funcs")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215925
Signed-off-by: Jim Quinlan <jim2101024@...il.com>
---
 drivers/pci/controller/pcie-brcmstb.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
index ba5c120816b2..adca74e235cb 100644
--- a/drivers/pci/controller/pcie-brcmstb.c
+++ b/drivers/pci/controller/pcie-brcmstb.c
@@ -540,16 +540,18 @@ static int pci_subdev_regulators_add_bus(struct pci_bus *bus)
 
 static int brcm_pcie_add_bus(struct pci_bus *bus)
 {
-	struct device *dev = &bus->dev;
 	struct brcm_pcie *pcie = (struct brcm_pcie *) bus->sysdata;
 	int ret;
 
-	if (!dev->of_node || !bus->parent || !pci_is_root_bus(bus->parent))
+	/* Only busno==1 requires us to linkup */
+	if ((int)bus->number != 1)
 		return 0;
 
 	ret = pci_subdev_regulators_add_bus(bus);
-	if (ret)
+	if (ret) {
+		pcie->refusal_mode = true;
 		return ret;
+	}
 
 	/* Grab the regulators for suspend/resume */
 	pcie->sr = bus->dev.driver_data;

base-commit: ef1302160bfb19f804451d0e919266703501c875
prerequisite-patch-id: 23a425390a4226bd70bbff459148c80f5e28379c
prerequisite-patch-id: e3f2875124b46b2b1cf9ea28883bf0c864b79479
prerequisite-patch-id: 9cdd706ee2038c7b393c4d65ff76a1873df1ca03
prerequisite-patch-id: 332ac90be6e4e4110e27bdd1caaff212c129f547
prerequisite-patch-id: 32a74f87cbfe9e8d52c34a4edeee6d271925665a
prerequisite-patch-id: f57cdf7ec7080bb8c95782bc7c3ec672db8ec1ce
prerequisite-patch-id: 18dc9236aed47f708f5c854afd832f3c80be5ea7
prerequisite-patch-id: dd147c6854c4ca12a9a8bd4f5714968a59d60e4e
-- 
2.17.1