On Friday 02 January 2015 17:13:19 Rob Herring wrote: > On Fri, Jan 2, 2015 at 2:52 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Friday 02 January 2015 12:14:43 Rob Herring wrote: > >> On Tue, Dec 30, 2014 at 3:58 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > >> > On Tuesday 30 December 2014 13:28:33 Rob Herring wrote: > >> > Maybe just return PCIBIOS_BAD_REGISTER_NUMBER in this case? > >> > >> Perhaps. We could probably simplify the config space read/write > >> functions and just provide the PCI core a bus/devfn/offset to config > >> address translation function. That would not work in all cases, but > >> propably most that have memory mapped config space. > > > > Actually, thinking about this some more, the implementation seems to > > be "CAM" compliant, and we could share the confic space accessors with > > the ones from drivers/pci/host/pci-host-generic.c. > > Almost. It uses readl for all size accesses. Yet writes support > different access sizes. I would guess that the h/w can support byte > and word reads if writes are supported, but I can't really verify. > Dword-only sized reads or reads and writes seem to be the main > variations for config space accesses. There's a few hosts with more > complex config space access setup, but quite a few only vary in > address decode. It was probably just done the current way because it seemed simpler at the time, but I agree that we can just keep it like this if there is any chance it's required as a workaround for a hardware glitch. With your other patch you just posted, it really becomes trivial to do. > >> I'm a bit puzzled myself. I think that the devices are not probed > >> until after pci_assign_unassigned_bus_resources. It certainly doesn't > >> work without that call. Really, I think of_irq_parse_and_map_pci > >> should be the default if no one else has set the device's irq (and the > >> host has a device node of course). > >> > >> It also seems to be a bit of random set of pci functions that are > >> called here. It would be nice to simplify this chunk of code. > > > > Yes, and we recently had some attempts at creating a better interface posted > > on the mailing list, not sure what the latest status on it is. I think we > > want to end up with a two-stage interface along the lines of: > > > > /* allocate a pci_host_bridge, scan DT, set default operations, map > > I/O space if necessary, request all resources ... */ > > phb = pci_host_bridge_create(parent, ..., sizeof(struct my_pci_private)); > > Humm, I wondered what happened to pci_host_bridge_create and thought > we had abandoned it. It wasn't too clear reading thru the threads. The > host drivers generally still have to walk thru the resources anyway to > setup inbound and outbound windows, so we don't gain too much moving > that out. I think the discussion has not ended yet, I'm still in favor of doing it like that. The current of_pci_get_host_bridge_resources() function is indeed lacking a bit because it just returns the resources that are needed for setting up the PCI side, but it doesn't provide a list of the host side windows that may need to get programmed into hardware registers on machines without a firmware that has set them up in advance (i.e. most ARM32 and MIPS32 machines). We could add another exported function to return those, or we could find a way to pass those back through the pci_host_bridge pointer from the common function. Setting up the PCI side by itself does seem useful to me though, mainly to prevent host controller drivers from getting it wrong. > And the error clean-up gets complicated too. In what way? I would hope that we could come up with a way to make pci_host_bridge_create() able to roll-back, so it does nothing in case of an error, and allocate all resources using devm_* so it all gets undone if probe() fails for another reason. Arnd -- 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
