From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Date: Thu, 20 Aug 2020 05:20:04 +0000 Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT Message-Id: <20200820052004.GA5305@lst.de> List-Id: References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-6-hch@lst.de> <20200819135454.GA17098@lst.de> <20200820044347.GA4533@lst.de> In-Reply-To: <20200820044347.GA4533@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tomasz Figa Cc: alsa-devel@alsa-project.org, linux-ia64@vger.kernel.org, Linux Doc Mailing List , nouveau@lists.freedesktop.org, linux-nvme@lists.infradead.org, linux-mips@vger.kernel.org, "James E.J. Bottomley" , linux-mm@kvack.org, Christoph Hellwig , linux-samsung-soc , Joonyoung Shim , linux-scsi@vger.kernel.org, Kyungmin Park , Ben Skeggs , Matt Porter , Linux Media Mailing List , Tom Lendacky , Pawel Osciak , Mauro Carvalho Chehab , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, Seung-Woo Kim , Linux Kernel Mailing List , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " 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.