On Thu, Oct 09, 2014 at 11:51:43AM +0100, Arnd Bergmann wrote: [...] > > Last changes where introduced by commit 8c05cd08a, whose commit log adds > > to my confusion: > > > > "[...] I think what we want here is for pci_start to be 0 when mmap_api == > > PCI_MMAP_PROCFS.[...]" > > > > But that's not what the code does. > > My best guess is that this is a typo and that Darrick meant PCI_MMAP_SYSFS > in the changelog, which is the same thing that the code does. It's also > the sensible thing to do. > > This probably means that the procfs interface is now also broken on > sparc. > > > I will try to grab an integrator board to give it a go. > > Ok, good idea. Grabbed, tested it, my theory was correct, I can't map PCI resources to userspace. Actually, if I pass resource offset as a fixed-up address, mmap succeeds through proc, but it does not mmap the resource, it maps the resource + mem_offset that happens to be RAM :D for the PCI slot I am using. I am testing on an oldish (3.16) kernel since I am having trouble with mainline PCI and my network adapter on integrator, but I do not see why this is a problem, this bug has been there forever. By removing mem_offset from pci_mmap_page_range() everything works fine, both proc and sys mappings are ok. > > > > Or we can add mem_offset to the host bridge (after all architectures like > > > > PowerPC and Microblaze have a pci_mem_offset variable in their host > > > > controllers), but still, this removes pci_sys_data dependency but does > > > > not solve the pci_mmap_page_range() issue. > > > > > > The host bridge already stores the mem_offset in terms of the resource > > > list, so we could readily use that, except that it might break the > > > powerpc hack if that is still in use. > > > > Well, yes, I am not saying it can't be done by using the resources list, > > I am just trying to understand if that's really useful. > > The PCI core tries to be ready for PCI host bridges that have multiple > discontiguous memory spaces with different offsets, although I don't know > of anybody has that. However if we decide to implement a generic > pci_mmap_page_range that tries to take the offset into account, we should > use the resource list in the host bridge because it can tell us the correct > offsets. > > However, given what you found, the procfs interface being broken since > 2010 on both architectures (arm32 and sparc) that try to honor the offset, > we should probably go back to your previous suggestion of removing > the offset handling, which would make it possible to use the procfs > interface and the sysfs interface on all architectures. > > Would you be able to prepare a patch that does this and circulate that > with the sparc, powerpc and microblaze maintainers as well as Darrick > and Martin who were involved with the pci_mmap_fits change? Yes, but let's step back a second. I think that the proc interface should expect an offset as passed to the user in /proc/bus/pci/devices, and there the resource is exposed through pci_resource_to_user(). Hence, the pci_mmap_fits() should check the offset against the resource filtered through pci_resource_to_user(), job done, patch is trivial, and does what pci_resource_to_user() was meant for IMHO. Then we have to decide what to do with arm32 code: 1) we remove mem_offset from pci_mmap_page_range() (and rely on default pci_resource_to_user()) or 2) we provide pci_resource_to_user() for arm32 which does the CPU->bus conversion for us (and leave mem_offset as-is in pci_mmap_range()) Thoughts ? Thanks, Lorenzo -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
