> This was a bit confusing following the previous paragraph. I meant to say that the > *saa7134* userptr implementation is not USERPTR at all but PAGE_ALIGNED_USERPTR. > > A proper USERPTR implementation (like in bttv) can use any malloc()ed pointer as > it should, but saa7134 can't as it requires the application to align the pointer > to a page boundary, which is non-standard. It's probably worth mentioning at this point that there's a bug in videobuf2_vmalloc() where it forces the buffer provided by userptr mode to be page aligned. This causes issues if you hand it a buffer that isn't actually page aligned, as it writes to an arbitrary offset into the buffer instead of the start of the buffer you provided. I've had the following patch in my private tree for months, but had been hesitant to submit it since I didn't know if it would effect other implementations. I wasn't sure if USERPTR mode required the buffers to be page aligned and I was violating the spec. Devin From: Devin Heitmueller <dheitmueller@xxxxxxxxxxxxxx> Date: Fri, 17 May 2013 19:53:02 +0000 (-0400) Subject: Fix alignment bug when using VB2 with userptr mode Fix alignment bug when using VB2 with userptr mode If we pass in a USERPTR buffer that isn't page aligned, the driver will align it (and not tell userland). The result is that the driver thinks the video starts in one place while userland thinks it starts in another. This manifests itself as the video being horizontally shifted and there being garbage from the start of the field up to that point. This problem was seen with both the em28xx and uvc drivers when testing on the Davinci platform (where the buffers allocated are not necessarily page aligned). --- diff --git a/linux/drivers/media/v4l2-core/videobuf2-vmalloc.c b/linux/drivers/media/v4l2-core/videobuf2-vmalloc.c index 94efa04..ad7ce7c 100644 --- a/linux/drivers/media/v4l2-core/videobuf2-vmalloc.c +++ b/linux/drivers/media/v4l2-core/videobuf2-vmalloc.c @@ -82,7 +82,7 @@ static void *vb2_vmalloc_get_userptr(void *alloc_ctx, unsigned long vaddr, return NULL; buf->write = write; - offset = vaddr & ~PAGE_MASK; + offset = 0; buf->size = size; -- Devin J. Heitmueller - Kernel Labs http://www.kernellabs.com -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
