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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 6E22CC43387 for ; Thu, 20 Dec 2018 17:39:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F08C2186A for ; Thu, 20 Dec 2018 17:39:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="oRDDkOJW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388058AbeLTRjx (ORCPT ); Thu, 20 Dec 2018 12:39:53 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:59490 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730526AbeLTRjw (ORCPT ); Thu, 20 Dec 2018 12:39:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=xlP1es0E/CTI638jb51O8he5KmaEfgJt9PkANcyjU3g=; b=oRDDkOJWpzAPLKWeA77FYj0CS HUNI2eP+1uUZC6AtOi5Hl7CdVhAkX+YfnSJxefY1LC6uMOSSkRttKoD/1x+o4RnXc0niNS0n86zoi 6WR4BZSgjflcoS9oDio47eqOsdY2As1ieaIl9fneGaSuIDoIee8E+I/u+02VUQ7vkGG931kkNqtvi WZGbZg+g7u1xS6Gd6kJajjJ90y5nel9tz/ironWn8I270eimHowAkRAUsfGAMEBRo+OfY1pw0kUAc iI5r8nKlk/e5SfV6tRyudC5V7qNR+X+F/DusFVXfs75NI1Qy3LSDFgwaeJ4jQaqqLnW9gnDF/feOh ZzxovbF7A==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1ga2IY-00075g-9x; Thu, 20 Dec 2018 17:39:50 +0000 Date: Thu, 20 Dec 2018 09:39:50 -0800 From: Christoph Hellwig To: Oleksandr Andrushchenko Cc: Christoph Hellwig , Noralf =?iso-8859-1?Q?Tr=F8nnes?= , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, daniel.vetter@intel.com, jgross@suse.com, boris.ostrovsky@oracle.com, Oleksandr Andrushchenko Subject: Re: [PATCH] drm/xen-front: Make shmem backed display buffer coherent Message-ID: <20181220173950.GA19641@infradead.org> References: <20181127103252.20994-1-andr2000@gmail.com> <17640791-5306-f7e4-8588-dd39c14e975b@tronnes.org> <20181220153646.GA22997@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 20, 2018 at 05:49:39PM +0200, Oleksandr Andrushchenko wrote: > This is the only patch [1], no series. And at the moment I think > there is nothing to review as I am not sure how to deal with those > shmem pages: this patch is rather to start a discussion on how shmem > pages can be flushed on ARM (the only workaround I have so far is > in this patch which uses DMA API). This is where I am looking for > some advice, so I can implement the patch the right way. shmem is basically page cache. So you need to use the DMA streaming API (dma_map_*) to map it for DMA. You need to make sure no one access the kernel mapping at the same time as you do DMA to it, so the pages should be locked. This is how the normal file system I/O path works.