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

[Bjorn Helgaas]

[+to Cyril]

Cyril, if you have a chance to test this and verify that it fixes the
regression, we may still be able to squeeze this into v5.18.

I can add the Reported-by and Tested-by tags myself.

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.
> 
> 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 at gmail.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
>