On Wed, Aug 19, 2020 at 3:55 PM Christoph Hellwig <hch@xxxxxx> wrote: > > On Wed, Aug 19, 2020 at 01:16:51PM +0200, Tomasz Figa wrote: > > Hi Christoph, > > > > On Wed, Aug 19, 2020 at 8:56 AM Christoph Hellwig <hch@xxxxxx> wrote: > > > > > > The V4L2-FLAG-MEMORY-NON-CONSISTENT flag is entirely unused, > > > > Could you explain what makes you think it's unused? It's a feature of > > the UAPI generally supported by the videobuf2 framework and relied on > > by Chromium OS to get any kind of reasonable performance when > > accessing V4L2 buffers in the userspace. > > Because it doesn't do anything except on PARISC and non-coherent MIPS, > so by definition it isn't used by any of these media drivers. It's still an UAPI feature, so we can't simply remove the flag, it must stay there as a no-op, until the problem is resolved. Also, it of course might be disputable as an out-of-tree usage, but selecting CONFIG_DMA_NONCOHERENT_CACHE_SYNC makes the flag actually do something on other platforms, including ARM64. Best regards, Tomasz
