On Tuesday 07 October 2014 15:47:50 Lorenzo Pieralisi wrote: > On Tue, Oct 07, 2014 at 02:52:27PM +0100, Arnd Bergmann wrote: > > On Tuesday 07 October 2014 13:06:59 Lorenzo Pieralisi wrote: > > > On Wed, Oct 01, 2014 at 10:38:45AM +0100, Arnd Bergmann wrote: > > > > > > [...] > > > > > > > pci_mmap_page_range could either get generalized some more in an attempt > > > > to have a __weak default implementation that works on ARM, or it could > > > > be changed to lose the dependency on pci_sys_data instead. In either > > > > case, the change would involve using the generic pci_host_bridge_window > > > > list. > > > > > > On ARM pci_mmap_page_range requires pci_sys_data to retrieve its > > > mem_offset parameter. I had a look, and I do not understand *why* > > > it is required in that function, so I am asking. That function > > > is basically used to map PCI resources to userspace, IIUC, through > > > /proc or /sysfs file mappings. As far as I understand those mappings > > > expect VMA pgoff to be the CPU address when files representing resources > > > are mmapped from /proc and 0 when mmapped from /sys (I mean from > > > userspace, then VMA pgoff should be updated by the kernel to map the > > > resource). > > > > Applying the mem_offset is certainly the more intuitive way, since > > that lets you read the PCI BAR values from a device and access the > > device with the appropriate offsets. > > Ok, but I am referring to this snippet (drivers/pci/pci-sysfs.c): > > /* pci_mmap_page_range() expects the same kind of entry as coming > * from /proc/bus/pci/ which is a "user visible" value. If this is > * different from the resource itself, arch will do necessary fixup. > */ > pci_resource_to_user(pdev, i, res, &start, &end); > > --> Here start represents a CPU physical address, if pci_resource_to_user() > does not fix it up, correct ? > > vma->vm_pgoff += start >> PAGE_SHIFT; > > [...] > > return pci_mmap_page_range(...); > > pci_mmap_page_range() applies (mem_offset >> PAGE_SHIFT) to pgoff in the > ARM implemention. > > Is not there a mismatch here on platforms where mem_offset != 0 ? Yes, I think that's right: ARM never gained its own pci_resource_to_user() implementation, presumably because nobody ran into this problem and debugged it all the way. Arnd -- 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
