Messages in this thread | | | Date | Tue, 18 Nov 2008 22:39:09 +0900 | From | Paul Mundt <> | Subject | Re: [PATCH] Video/UVC: Port mainlined uvc video driver to NOMMU |
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On Fri, Nov 14, 2008 at 12:52:10AM +0100, Laurent Pinchart wrote: > On Monday 10 November 2008, Hennerich, Michael wrote: > > >On Thursday 06 November 2008, Bryan Wu wrote: > > > > @@ -1071,7 +1072,20 @@ static int uvc_v4l2_mmap(struct file *file, > > > > struct vm_area_struct *vma) addr += PAGE_SIZE; > > > > size -= PAGE_SIZE; > > > > } > > > > +#else > > > > + if (i == video->queue.count || > > > > + PAGE_ALIGN(size) != video->queue.buf_size) { > > > > > > Just out of curiosity, why do you need to PAGE_ALIGN size for non-MMU > > > platforms ? > > > > Size and video->queue.buf_size is not the 100% same size (off by a few > > bytes < pagesize), I think it's because on NOMMU the kernel calls > > kmalloc() to allocate the buffer, not get_free_page(). > > That's right, but only for private mappings. It makes little sense to create a > private mapping on a V4L2 device as the kernel will read() device data into > the buffer when mapping the device (at least on NOMMU platforms). Only shared > mappings make sense in this case. > The change itself is crap anyways, since it is just working around the fact that vm_insert_page() presently -EINVAL's out on nommu. The vmalloc_to_page()/vm_insert_page() pair is used extensively across the v4l drivers, and it's unrealistic to expect to patch every call site with this sort of a workaround.
While we can't support vm_insert_page() in most cases, these sorts of use cases where it is just iterating over a contiguous block of pages on a VMA that has already been established is something that can at least be handled fairly easily (in this case, even just doing nothing in vm_insert_page() would likely give the desired result, although we ought to fix up vm_insert_page() to do something more useful instead). Working out the bounds of the VMA isn't exactly difficult either, since we have all of that already filled in the VMA by the time vma_insert_page() is called.
Regarding the VMA flag, this can be rectified by providing a dummy get_unmapped_area() for the v4l devices which will set some default capabilities. After that, determine_vm_flags() should take care of setting up the proper VMA flags without hacking every driver's mmap() routine. This sort of thing has absolutely no place in the driver, though.
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