From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH] drm/xen-front: Make shmem backed display buffer coherent Date: Thu, 20 Dec 2018 09:39:50 -0800 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="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by gabe.freedesktop.org (Postfix) with ESMTPS id 228E36F485 for ; Thu, 20 Dec 2018 17:39:53 +0000 (UTC) Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Oleksandr Andrushchenko Cc: jgross@suse.com, Oleksandr Andrushchenko , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Christoph Hellwig , daniel.vetter@intel.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com List-Id: dri-devel@lists.freedesktop.org T24gVGh1LCBEZWMgMjAsIDIwMTggYXQgMDU6NDk6MzlQTSArMDIwMCwgT2xla3NhbmRyIEFuZHJ1 c2hjaGVua28gd3JvdGU6Cj4gVGhpcyBpcyB0aGUgb25seSBwYXRjaCBbMV0sIG5vIHNlcmllcy4g QW5kIGF0IHRoZSBtb21lbnQgSSB0aGluawo+IHRoZXJlIGlzIG5vdGhpbmcgdG8gcmV2aWV3IGFz IEkgYW0gbm90IHN1cmUgaG93IHRvIGRlYWwgd2l0aCB0aG9zZQo+IHNobWVtIHBhZ2VzOiB0aGlz IHBhdGNoIGlzIHJhdGhlciB0byBzdGFydCBhIGRpc2N1c3Npb24gb24gaG93IHNobWVtCj4gcGFn ZXMgY2FuIGJlIGZsdXNoZWQgb24gQVJNICh0aGUgb25seSB3b3JrYXJvdW5kIEkgaGF2ZSBzbyBm YXIgaXMKPiBpbiB0aGlzIHBhdGNoIHdoaWNoIHVzZXMgRE1BIEFQSSkuIFRoaXMgaXMgd2hlcmUg SSBhbSBsb29raW5nIGZvcgo+IHNvbWUgYWR2aWNlLCBzbyBJIGNhbiBpbXBsZW1lbnQgdGhlIHBh dGNoIHRoZSByaWdodCB3YXkuCgpzaG1lbSBpcyBiYXNpY2FsbHkgcGFnZSBjYWNoZS4gIFNvIHlv dSBuZWVkIHRvIHVzZSB0aGUgRE1BIHN0cmVhbWluZwpBUEkgKGRtYV9tYXBfKikgdG8gbWFwIGl0 IGZvciBETUEuICBZb3UgbmVlZCB0byBtYWtlIHN1cmUgbm8gb25lCmFjY2VzcyB0aGUga2VybmVs IG1hcHBpbmcgYXQgdGhlIHNhbWUgdGltZSBhcyB5b3UgZG8gRE1BIHRvIGl0LApzbyB0aGUgcGFn ZXMgc2hvdWxkIGJlIGxvY2tlZC4gIFRoaXMgaXMgaG93IHRoZSBub3JtYWwgZmlsZSBzeXN0ZW0K SS9PIHBhdGggd29ya3MuCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fCmRyaS1kZXZlbCBtYWlsaW5nIGxpc3QKZHJpLWRldmVsQGxpc3RzLmZyZWVkZXNrdG9w Lm9yZwpodHRwczovL2xpc3RzLmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2RyaS1k ZXZlbAo= 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 ; 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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.