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). Question is: why pci_mmap_page_range() should apply an additional shift to the VMA pgoff based on pci_sys_data.mem_offset, which represents the offset from cpu->bus offset. I do not understand that. PowerPC does not seem to apply that fix-up (in PowerPC __pci_mmap_make_offset there is commented out code which prevents the pci_mem_offset shift to be applied). I think it all boils down to what the userspace interface is expecting when the memory areas are mmapped, if anyone has comments on this that is appreciated. 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
