Messages in this thread | | | Date | Thu, 5 Feb 2009 17:10:22 +0800 | Subject | Re: [PATCH] Video/UVC: Port mainlined uvc video driver to NOMMU | From | Bryan Wu <> |
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On Tue, Nov 18, 2008 at 9:39 PM, Paul Mundt <lethal@linux-sh.org> wrote: > 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. >
Hi Laurent,
Does this patch make sense? I hope you understand the tricky things in nommu mapping world.
Thanks -Bryan
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