On Tue, Nov 11, 2014 at 4:48 AM, Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> wrote: > On Mon, Nov 10, 2014 at 11:04:54PM +0000, Bjorn Helgaas wrote: >> ... >> Here's what I think I understand so far: >> >> Applications can mmap PCI memory space via either sysfs or procfs (the >> procfs method is deprecated but still supported): >> >> - In sysfs, there's a separate /sys/devices/pci*/.../resource* file >> for each device BAR, and the application opens the appropriate >> file and supplies the offset from the beginning of the BAR as the >> mmap(2) offset. >> >> - In procfs, the application opens the single /proc/bus/pci/... file >> for the device. On most platforms, it supplies the CPU physical >> address as the mmap(2) offset. On a few platforms, such as SPARC, >> it supplies the bus address, i.e., a BAR value, instead. >> >> But I'm not sure I have this right. If the procfs offset is either the >> CPU physical address or the BAR value, then pci_resource_to_user() >> should be (depending on the arch) either a no-op or use >> pci_resource_to_bus(). > > Exactly (pcibios_resource_to_bus() ?). > >> But that's not how it's implemented. Maybe it *could* be? If >> pci_resource_to_user() gives you something that's not a CPU physical >> address and not a bus address, what *does* it give you, and why would we >> need this third kind of thing? > > Well, you need a per arch function implementation where to define if > the conversion from CPU physical address to PCI bus should take place > or not right ? As you mentioned above, if that should be a per-arch > decision, there has to be a per-arch function to filter the resource > in question, I guess that's my understanding behind pci_resource_to_user(), > but I am not sure either, and understanding that was the primary reason > for this patchset so comments are welcome. I agree that we need pci_resource_to_user() because arches do different things, so we can't just remove pci_resource_to_user() and replace it with pci_resource_to_bus(). My point is that we have a generic pci_resource_to_user() implementation that does nothing, and if an arch *does* implement its own pci_resource_to_user(), it seems like it should simply call pci_resource_to_user(). Bjorn -- 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
