[+cc Loongson folks, thread at https://lore.kernel.org/r/20230521115141.2384444-1-vladimir.oltean@xxxxxxx] On Wed, May 31, 2023 at 07:58:19PM +0300, Vladimir Oltean wrote: > On Wed, May 31, 2023 at 11:56:02AM -0500, Bjorn Helgaas wrote: > > What bad things happen without this patch? > > It's in the commit title: probing the entire device (PCI device!!!) is > skipped if function 0 has status = "disabled". Aka PCIe functions 1, 2, 3, 4, ... I guess I should have asked "what bad things happen without this patch and without the DT 'disabled' status"? I think 6fffbc7ae137 ("PCI: Honor firmware's device disabled status") was basically a workaround for Loongson making a device visible in PCI config space when it shouldn't have been [1]. 6fffbc7ae137 [2] means we pretend the PCI device doesn't exist if DT status is "disabled". If the device happens to be Function 0, that means we don't look for any more functions. I guess that doesn't matter for Loongson. But it does matter for this NXP platform, where we don't want to use Function 0, but we *do* want to use other Functions. There are several PCIe things that are required to be in Function 0 (MPS, ASPM, IDE, CMA/SPDM, etc), at least in certain cases. What would happen if instead of making pci_setup_device() fail (as both 6fffbc7ae137 and this patch do, which means the device doesn't even show up in "lspci"), we just prevent drivers from binding to it, e.g., by making pci_device_probe() fail? The device would then appear in "lspci" and the PCI core would configure things as usual, but no drivers would be able to claim it. Bjorn [1] https://lore.kernel.org/all/20221114074346.23008-1-liupeibao@xxxxxxxxxxx/ [2] https://git.kernel.org/linus/6fffbc7ae137
