On Tue, Nov 11, 2014 at 02:20:31PM +0000, Bjorn Helgaas wrote: > 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(). to_bus() you mean. Well, I agree, but I am not sure it would work on all arches that deviate from the generic implementation, I can't speak for other architectures since I do not have an in-depth knowledge of their PCI internal implementations, in particular in relation to CPU <-> PCI address map conversions/mappings. I read your comment as an agreement on the approach I took in my patch, except for the current pci_resource_to_user() implementation(s), which I did not touch. Thanks, Lorenzo -- 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
