On Wed, Dec 27, 2017 at 12:45:42PM -0600, Bjorn Helgaas wrote:

[...]

quoted

+		/* Set up class code for MT7622 */
+		val = PCI_CLASS_BRIDGE_PCI << 16;
+		writel(val, port->base + PCIE_CONF_CLASS);

1) Your comments mention MT7622 specifically, but this code is run for
both mt2712-pcie and mt7622-pcie.  If this code is safe and necessary
for both mt2712-pcie and mt7622-pcie, please remove the mention of
MT7622.

2) The first comment mentions both "vendor ID and device ID" but you
don't write the device ID.  Since this code applies to both
mt2712-pcie and mt7622-pcie, my guess is that you don't *want* to
write the device ID.  If that's the case, please fix the comment.

3) If you only need to set the vendor ID, you're performing a 32-bit
write (writel()) to update a 16-bit value.  Please use writew()
instead.

4) If you only need to set the vendor ID, please use a definition like
"PCIE_CONF_VENDOR_ID" instead of the ambiguous "PCIE_CONF_ID".

5) If you only need to set the vendor ID, please update the changelog
to mention "vendor ID" specifically instead of the ambiguous "IDs".

6) Please add a space before the closing "*/" of the first comment.

7) PCI_CLASS_BRIDGE_PCI is for a PCI-to-PCI bridge, i.e., one that has
PCI on both the primary (upstream) side and the secondary (downstream)
side.  That kind of bridge has a type 1 config header (see
PCI_HEADER_TYPE) and the PCI_PRIMARY_BUS and PCI_SECONDARY_BUS
registers tell us the bus number of the primary and secondary sides.

I don't believe this device is a PCI-to-PCI bridge.  I think it's a
*host* bridge that has some non-PCI interface on the upstream side and
should have a type 0 config header.  If that's the case you should use
PCI_CLASS_BRIDGE_HOST instead.

I think these registers actually programme the root port register space
in the RC (whether real or fake - that depends on the RC design) so
the class is PCI_CLASS_BRIDGE_PCI, that's what most of host bridge
drivers in drivers/pci/host do.

I would like to get to the bottom of this since it is indeed misleading
(and I do not have HW to test it myself to check my understanding).

Thanks,
Lorenzo