Re: [PATCH v3 3/4] PCI/ACPI: Add Broadcom bcm2711 MCFG quirk

Bjorn Helgaas
2021-10-05T15:10:45Z

On Thu, Aug 26, 2021 at 02:15:56AM -0500, Jeremy Linton wrote:
> Now that there is a bcm2711 quirk, it needs to be enabled when the
> MCFG is missing. Use an ACPI namespace _DSD property
> "linux-ecam-quirk-id" as an alternative to the MCFG OEM.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> Acked-by: Florian Fainelli <f.fainelli@gmail.com>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
> drivers/acpi/pci_mcfg.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/drivers/acpi/pci_mcfg.c b/drivers/acpi/pci_mcfg.c
> index 53cab975f612..04c517418365 100644
> --- a/drivers/acpi/pci_mcfg.c
> +++ b/drivers/acpi/pci_mcfg.c
> @@ -169,6 +169,9 @@ static struct mcfg_fixup mcfg_quirks[] = {
> ALTRA_ECAM_QUIRK(1, 13),
> ALTRA_ECAM_QUIRK(1, 14),
> ALTRA_ECAM_QUIRK(1, 15),
> +
> + { "bc2711", "", 0, 0, MCFG_BUS_ANY, &bcm2711_pcie_ops,
> + DEFINE_RES_MEM(0xFD500000, 0xA000) },
> };
>
> static char mcfg_oem_id[ACPI_OEM_ID_SIZE];
> @@ -198,8 +201,22 @@ static void pci_mcfg_apply_quirks(struct acpi_pci_root *root,
> u16 segment = root->segment;
> struct resource *bus_range = &root->secondary;
> struct mcfg_fixup *f;
> + const char *soc;
> int i;
>
> + /*
> + * This may be a machine with a PCI/SMC conduit, which means it doesn't
> + * have an MCFG. Use an ACPI namespace definition instead.
> + */
> + if (!fwnode_property_read_string(acpi_fwnode_handle(root->device),
> + "linux-ecam-quirk-id", &soc)) {
> + if (strlen(soc) != ACPI_OEM_ID_SIZE)

From a reviewing perspective, it's not obvious why soc must be exactly
ACPI_OEM_ID_SIZE. Does that imply space-padding in the DT string or
something?

Is there any documentation for this DT property?

Also not obvious why strlen() is safe here. I mean, I looked a couple
levels deep in fwnode_property_read_string(), but whatever guarantees
null termination is buried pretty deep.

It seems a little weird to use an MCFG quirk mechanism when there's no
MCFG at all on this platform.

> + dev_err(&root->device->dev, "ECAM quirk should be %d characters\n",
> + ACPI_OEM_ID_SIZE);
> + else
> + memcpy(mcfg_oem_id, soc, ACPI_OEM_ID_SIZE);
> + }
> +
> for (i = 0, f = mcfg_quirks; i < ARRAY_SIZE(mcfg_quirks); i++, f++) {
> if (pci_mcfg_quirk_matches(f, segment, bus_range)) {
> if (f->cfgres.start)
> --
> 2.31.1
>