Messages in this thread | | | Subject | Re: [PATCH v3 3/4] PCI/ACPI: Add Broadcom bcm2711 MCFG quirk | From | Jeremy Linton <> | Date | Tue, 5 Oct 2021 18:32:26 -0500 |
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Hi,
On 10/5/21 5:31 PM, Bjorn Helgaas wrote: > On Tue, Oct 05, 2021 at 10:43:32AM -0500, Jeremy Linton wrote: >> On 10/5/21 10:10 AM, Bjorn Helgaas wrote: >>> 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? >> >> This is at the moment an ACPI only DSD, and it must follow the MADT OEM_ID >> format for now because we are effectively just overriding that field. The >> rest of the code in this module is just treating it as a fixed 6 bytes. >> >>> Is there any documentation for this DT property? >> >> Its not a DT property, and its unclear since its linux only if it >> belongs in previously linked ACPI registry. > > Oh, right, it comes from a _DSD. > >>> 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. >> >> I've not tracked down who, if anyone other than the AML compiler is >> guaranteeing a null. The spec says something to the effect "Most other >> string, however, are of variable-length and are automatically null >> terminated by the compiler". Not sure if that helps any. > > Doesn't help for me. The PCI core shouldn't go in the weeds no matter > what junk we might get from an AML compiler. Maybe > fwnode_property_read_string() guarantees null termination, but it's > not documented and not easy to verify. > > I think a strncpy() here might be better. Not sure it's worthwhile to > emit a specific error message for the wrong length.
I think we went around about this a bit, but yes strncpy() is exactly what we want because the rest of the code assumes 6 non-null terminated characters and strncpy won't terminate it if its longer. OTOH, i'm not sure we really want shorter strings padded with nulls either.
strncpy() is easy though, so sure. <shrug>
> >>> It seems a little weird to use an MCFG quirk mechanism when there's no >>> MCFG at all on this platform. >> >> Well its just a point to hook in a CFG space quirk, and since that >> is what most of the MCFG quirks are, it seemed reasonable to reuse >> it rather than recreate it. > > Yeah, it's ugly no matter how we slice it. The pci_no_msi() > especially has nothing to do with ECAM at all. But I don't know how > to identify this thing for a quirk. PNP0A08 devices really rely on > ECAM or a system firmware config accessor. > >>>> + 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 >>>> >>
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