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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 80AC5C2D0A8 for ; Mon, 28 Sep 2020 13:31:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22A4920759 for ; Mon, 28 Sep 2020 13:31:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=crapouillou.net header.i=@crapouillou.net header.b="P4xXMCay" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726460AbgI1Nbn (ORCPT ); Mon, 28 Sep 2020 09:31:43 -0400 Received: from crapouillou.net ([89.234.176.41]:54178 "EHLO crapouillou.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726327AbgI1Nbn (ORCPT ); Mon, 28 Sep 2020 09:31:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1601299899; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0SzWACBuI9QMwCiW7RkNoVRmCLnHWeSCxcbUL7DcVfc=; b=P4xXMCayyWAAUDEbXfTSxFl4XMI4I4+bQRS2Qk7dt0KhWyH5QLZ1rKOaIo3hAxLyYoHIxC r6YtBANmwXXU6POC+6apbG+i/HWU/ed63WaAfGWgrKlrr7kaoa0PEVoQKKY3vISb3E/yBG NucA0ykHdNpTVz8EiYXLt+7u6qAwppU= Date: Mon, 28 Sep 2020 15:31:28 +0200 From: Paul Cercueil Subject: Re: linux-next: build failure after merge of the drm tree To: Christoph Hellwig Cc: Stephen Rothwell , Dave Airlie , DRI , Linux Next Mailing List , Linux Kernel Mailing List Message-Id: In-Reply-To: <20200928121002.GA3219@lst.de> References: <20200928135405.73404219@canb.auug.org.au> <20200928060427.GA15041@lst.de> <20200928113415.GA555@lst.de> <72ADHQ.T6LL1SHQF0RG3@crapouillou.net> <20200928121002.GA3219@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org Le lun. 28 sept. 2020 =E0 14:10, Christoph Hellwig a =E9crit=20 : > On Mon, Sep 28, 2020 at 01:46:55PM +0200, Paul Cercueil wrote: >>> dma_mmap_attrs can only be used on allocations from dma_mmap_attrs=20 >>> with >>> the same attrs. As there is no allocation using=20 >>> DMA_ATTR_NON_CONSISTENT >>> in the drm core, something looks very fishy here. >>=20 >> Is that a fact? I don't see why you couldn't change the cache=20 >> settings >> after allocation. In practice it works just fine. >=20 > Accessing the same physical address using different caching attributes > is undefined behavior and fairly dangerous on most architectures, and > thus not supported by the DMA API. It's allocated with dma_alloc_wc, but then it's only accessed as=20 non-coherent. Anyway, for the time being I guess you could revert 37054fc81443. But I=20 have patches on top of it in drm-misc-next so it's going to be a mess. If we have time I can come up with a custom dumb_create() fonction, to=20 make sure that the GEM buffers are allocated with=20 dma_alloc_noncoherent(). Is there a dma_mmap_noncoherent() too? -Paul