On Mon, Dec 07, 2015 at 09:38:33AM -0600, Bjorn Helgaas wrote: > On Sat, Dec 05, 2015 at 11:38:37AM +0100, Geert Uytterhoeven wrote: > > Hi Bjorn, > > > > On Fri, Dec 4, 2015 at 10:26 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > On Tue, Dec 01, 2015 at 04:24:30PM +0900, Simon Horman wrote: > > >> Simply document new compat strings. > > >> There appears to be no need for a driver updates. > > >> > > >> Signed-off-by: Simon Horman <horms+renesas@xxxxxxxxxxxx> > > >> --- > > >> Documentation/devicetree/bindings/pci/pci-rcar-gen2.txt | 1 + > > >> 1 file changed, 1 insertion(+) > > >> > > >> diff --git a/Documentation/devicetree/bindings/pci/pci-rcar-gen2.txt b/Documentation/devicetree/bindings/pci/pci-rcar-gen2.txt > > >> index b19be08a8113..7c231b3e5872 100644 > > >> --- a/Documentation/devicetree/bindings/pci/pci-rcar-gen2.txt > > >> +++ b/Documentation/devicetree/bindings/pci/pci-rcar-gen2.txt > > >> @@ -8,6 +8,7 @@ OHCI and EHCI controllers. > > >> Required properties: > > >> - compatible: "renesas,pci-r8a7790" for the R8A7790 SoC; > > >> "renesas,pci-r8a7791" for the R8A7791 SoC; > > >> + "renesas,pci-r8a7793" for the R8A7793 SoC; > > > > > > What's the benefit of adding a string here if the driver doesn't check > > > for it? Since the driver doesn't look for it, there's no way to test > > > anything. > > > > If we ever discover a difference between PCI on r8a7793 compared to PCI on > > other SoCs of the R-Car Gen2 family, we can handle that difference in the > > driver. > > > > > It doesn't seem like this file is an authoritative source of names, so > > > > Yes it is. When adding compatible values to a DTS, checkpatch.pl will check > > for their existence in the binding documentation. Hence we always add the > > compatible values to the DT binding docs, before we start using them. > > > > > if we add it here, there's the possibility the r8a7793 will be > > > canceled or renamed, and then we'd have to update this if the driver > > > ever did need an r8a7793-specific quirk. If we waited until the > > > > I don't understand what you mean here. > > > > > driver actually needs a quirk, then we'd know exactly what name to > > > look for and we could update the driver, DT, and doc all together. > > > > If we update driver, DT, and doc only after we discover the need for a quirk, > > it's already too late, due to stable DT rules. Hence we always document and > > use SoC-specific compatible values, sometimes combined with family-specific > > compatible values. The driver only matches to the as least specific value as > > possible. > > The stable DT rules seem to be the key here, but I don't know what > they are. I found Documentation/devicetree/bindings/ABI.txt, but it > doesn't clear it up for me. > > I was assuming vendors could ship a DT in a platform ROM, in the same > way platforms ship with an ACPI system description. For ACPI, the > _HID/_CID in the ROM in the field is authoritative in the sense that > we have to regard it as a fixed, unchangeable feature of the platform. > If we want a driver to recognize that device, we have to build the ID > from the ROM into the driver, and it doesn't matter what is documented > in the spec or in the kernel source. > > If we had a one-sentence description of why adding the doc update when > we actually need it is too late, that would probably be enough. I agree that would be useful. > I'm perfectly happy with the PCI changes, so if somebody else wants to > just merge all these via a DT tree, I'm happy to ack the PCI ones. I have no fixed ideas about who should take these changes but I think you could take them through the PCI tree if you are so inclined. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
