Re: POSSIBLE REGRESSION: PCI/pwrctrl: Skip scanning for the device further if pwrctrl device is created

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, May 05, 2025 at 01:39:39PM -0400, Jim Quinlan wrote:
> Hello,
> 
> I recently rebased to the latest Linux master
> 
> ebd297a2affa Linus.Torvalds Merge tag 'net-6.15-rc5' of
> git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
> 
> and noticed that PCI is broken for
> "drivers/pci/controller/pcie-brcmstb.c"  I've bisected this to the
> following commit
> 
> 2489eeb777af PCI/pwrctrl: Skip scanning for the device further if
> pwrctrl device is created
> 
> which is part of the series [1].  The driver in pcie-brcmstb.c is
> expecting the add_bus() method to be invoked twice per boot-up, but
> the second call does not happen.  Not only does this code in
> brcm_pcie_add_bus() turn on regulators, it also subsequently initiates
> PCIe linkup.
> 
> If I revert the aforementioned commit, all is well.
> 
> FWIW, I have included the relevant sections of the PCIe DT we use at [2].

Mani, Bartosz, where are we at with this?  The 2489eeb777af commit log
doesn't mention a problem fixed by that commit; it sounds more like an
optimization -- just avoiding an unnecessary scan.

2489eeb777af appeared in v6.15-rc1, so there's still time to revert it
before v6.15 if that's the right way to fix this regression.

> [1] https://lore.kernel.org/lkml/20241231-pci-pwrctrl-slot-v2-0-6a15088ba541@linaro.org/T/#t
> [2]
> 
> pcie@1000110000 {
>         reg = <0x10 0x110000 0x0 0x9130>;
>         ...
> 
>         pci@0,0 {
>                 vpcie3v3-supply = <0x45>;
>                 vpcie12v-supply = <0x44>;
>                 reg = <0x0 0x0 0x0 0x0 0x0>;
>                 ranges;
>                 bus-range = <0x1 0xff>;
>                 compatible = "pciclass,0604";
>                 device_type = "pci";
>                 #address-cells = <0x3>;
>                 #size-cells = <0x2>;
> 
>                 pci-ep@0,0 {
>                         local-mac-address = [ 00 10 18 f0 35 55 ];
>                         reg = <0x10000 0x0 0x0 0x0 0x0>;
>                 };
>         };
> }