On Thu, Aug 20, 2020 at 06:43:47AM +0200, Christoph Hellwig wrote:
On Wed, Aug 19, 2020 at 03:57:53PM +0200, Tomasz Figa wrote:
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.
Ok, I'll switch to just ignoring it for the next version.
So I took a deeper look. I don't really think it qualifies as a UAPI in our traditional sense. For one it only appeared in 5.9-rc1, so we can trivially expedite the patch into 5.9-rc and not actually make it show up in any released kernel version. And even as of the current Linus' tree the only user is a test driver. So I really think the best way to go ahead is to just revert it ASAP as the design wasn't thought out at all.