From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6A3BCC433ED for ; Thu, 20 Aug 2020 04:44:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4939C20786 for ; Thu, 20 Aug 2020 04:44:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725838AbgHTEny (ORCPT ); Thu, 20 Aug 2020 00:43:54 -0400 Received: from verein.lst.de ([213.95.11.211]:40376 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725772AbgHTEnx (ORCPT ); Thu, 20 Aug 2020 00:43:53 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 5BE8868BEB; Thu, 20 Aug 2020 06:43:47 +0200 (CEST) Date: Thu, 20 Aug 2020 06:43:47 +0200 From: Christoph Hellwig To: Tomasz Figa Cc: Christoph Hellwig , Mauro Carvalho Chehab , Thomas Bogendoerfer , "James E.J. Bottomley" , Joonyoung Shim , Seung-Woo Kim , Kyungmin Park , Ben Skeggs , Pawel Osciak , Marek Szyprowski , Matt Porter , "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , Tom Lendacky , alsa-devel@alsa-project.org, linux-samsung-soc , linux-ia64@vger.kernel.org, linux-scsi@vger.kernel.org, linux-parisc@vger.kernel.org, Linux Doc Mailing List , nouveau@lists.freedesktop.org, Linux Kernel Mailing List , linux-nvme@lists.infradead.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , Linux Media Mailing List Subject: Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT Message-ID: <20200820044347.GA4533@lst.de> References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-6-hch@lst.de> <20200819135454.GA17098@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org 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. > 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. It isn't just disputable, but by kernel policies simply is not relevant.