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, HEADER_FROM_DIFFERENT_DOMAINS,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 0E741C43387 for ; Wed, 16 Jan 2019 06:36:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD58E20840 for ; Wed, 16 Jan 2019 06:36:38 +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="r+C0N8SN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387943AbfAPGgh (ORCPT ); Wed, 16 Jan 2019 01:36:37 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:56026 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730938AbfAPGgg (ORCPT ); Wed, 16 Jan 2019 01:36:36 -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=Y3Cfd4hD9ItjyLiX9AKzSPaNAJ0TUVsQI0XwBuOzzUU=; b=r+C0N8SNJQksJTXIEK8l1jSU7 0ZU7Qe5WFurFX8kdHS8yN/Vx+NZ80+UiHMFNwl8AmyUsTBd+Ki1jU+UbhPzN7K57IA220tDAB3Fa6 opy9l1gUmg8Mc9NqBXiZghu+UBFOLVIaAMoWsNr8cFHwFqmzUxk1aSYQaKr4U0JsLj8ijU43+aaAf RipQxP0294S2bIxwB122e05L8j46kCLTqtK31PqdXEsjoC+pUoOqWfNloRuaQlDnlaAP3/91k6MeT vVZMwz0D/AiQiAUbdEJRQO9mx14sZ41aEsoc4fht43sGluYmS73B8jGD1maExYifyuhEvBpie8ACW ICA4SxnfA==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gjeoR-0004Ct-AY; Wed, 16 Jan 2019 06:36:31 +0000 Date: Tue, 15 Jan 2019 22:36:31 -0800 From: Christoph Hellwig To: Gerd Hoffmann Cc: Oleksandr Andrushchenko , 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, noralf@tronnes.org, hch@infradead.org, Oleksandr Andrushchenko Subject: Re: [PATCH v2] drm/xen-front: Make shmem backed display buffer coherent Message-ID: <20190116063631.GA10881@infradead.org> References: <20190115140420.4652-1-andr2000@gmail.com> <20190116063002.jq3aas6ofhaogmyk@sirius.home.kraxel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190116063002.jq3aas6ofhaogmyk@sirius.home.kraxel.org> 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 Wed, Jan 16, 2019 at 07:30:02AM +0100, Gerd Hoffmann wrote: > Hi, > > > + if (!dma_map_sg(dev->dev, xen_obj->sgt->sgl, xen_obj->sgt->nents, > > + DMA_BIDIRECTIONAL)) { > > + ret = -EFAULT; > > + goto fail_free_sgt; > > + } > > Hmm, so it seems the arm guys could not come up with a suggestion how to > solve that one in a better way. Ok, lets go with this then. > > But didn't we agree that this deserves a comment exmplaining the purpose > of the dma_map_sg() call is to flush caches and that there is no actual > DMA happening here? Using a dma mapping call to flush caches is complete no-go. But the real question is why you'd even want to flush cashes if you do not want a dma mapping? This whole issue keeps getting more and more confusing.