Hi,

On 10/5/21 5:31 PM, Bjorn Helgaas wrote:

On Tue, Oct 05, 2021 at 10:43:32AM -0500, Jeremy Linton wrote:

quoted

On 10/5/21 10:10 AM, Bjorn Helgaas wrote:

quoted

On Thu, Aug 26, 2021 at 02:15:56AM -0500, Jeremy Linton wrote:

quoted

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 <redacted>
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.

quoted

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.

quoted

quoted

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>

quoted

quoted

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.

quoted

quoted

quoted

+			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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