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=-1.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 0E50FC43387 for ; Wed, 16 Jan 2019 00:33:52 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D092D20657 for ; Wed, 16 Jan 2019 00:33:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Cjf1ktXk" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D092D20657 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Mime-Version:References:In-Reply-To: Date:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Gz1KhR4ouHc5nmPBbcuOX1tuC7rhRV+mZA1Tgfk0dS0=; b=Cjf1ktXk/NKAc6 QV4cpHvy0IrtkweSOwvX+k3fVrZPH1fwrG3htsKq51gnvLM9GJo2Elb77FIy/rkYyva+JNyU+cBz6 U7blYF2IKjP1C83pE4tcR+a/tLoGwBghBBclFOasm0h0Xc2HQv0HjP16xHj01V0iLWoqzHCImqWJK TmitMGl7+tHdVAS2Rbbk/yrt0WwBlcuNLniKGAU80URk8aSoroxy8TkJF2g59jykvTGX30vdrcWFN 9jkIA5FhyrllvLCmKPLdHrbskbwlkVkFmd1RS89koik8hZ/KPvtd8Vnzk0z1rPj7IIhN9TzaWOmWI 9Bi3t/dCjYTm/RPKreYA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gjZ9Q-0001XD-UU; Wed, 16 Jan 2019 00:33:48 +0000 Received: from gate.crashing.org ([63.228.1.57]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gjZ9N-0001WS-Vs for linux-arm-kernel@lists.infradead.org; Wed, 16 Jan 2019 00:33:47 +0000 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x0G0X6xW011333; Tue, 15 Jan 2019 18:33:08 -0600 Message-ID: Subject: Re: [RFC PATCH] drm/ttm: force cached mappings for system RAM on ARM From: Benjamin Herrenschmidt To: Michael Ellerman , Will Deacon , "Koenig, Christian" Date: Wed, 16 Jan 2019 11:33:06 +1100 In-Reply-To: <87a7k2yx66.fsf@concordia.ellerman.id.au> References: <20190110072841.3283-1-ard.biesheuvel@linaro.org> <5d8135de-80fe-9c0e-2206-ecb809f64cdb@daenzer.net> <55facfb9-92af-86b8-40e9-d63b887b5592@amd.com> <9f956898-7973-98ee-6bf1-e1d445e9d365@amd.com> <20190114191350.GA29600@fuggles.cambridge.arm.com> <20190114193548.GB29600@fuggles.cambridge.arm.com> <87a7k2yx66.fsf@concordia.ellerman.id.au> User-Agent: Evolution 3.30.4 (3.30.4-1.fc29) Mime-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190115_163346_237542_54B1D027 X-CRM114-Status: GOOD ( 11.38 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Carsten Haitzler , Ard Biesheuvel , David Airlie , Michel =?ISO-8859-1?Q?D=E4nzer?= , Linux Kernel Mailing List , dri-devel , "Huang, Ray" , "Zhang, Jerry" , linux-arm-kernel , Bernhard =?ISO-8859-1?Q?Rosenkr=E4nzer?= Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 2019-01-15 at 22:31 +1100, Michael Ellerman wrote: > > > As far as I know Power doesn't really supports un-cached memory at all, > > > except for a very very old and odd configuration with AGP. > > > > Hopefully Michael/Ben can elaborate here, but I was under the (possibly > > mistaken) impression that mismatched attributes could cause a machine-check > > on Power. > > That's what I've always been told, but I can't actually find where it's > documented, I'll keep searching. > > But you're right that mixing cached / uncached is not really supported, > and probably results in a machine check or worse. .. or worse :) It could checkstop. It's also my understanding that on ARM v7 and above, it's technically forbidden to map the same physical page with both cached and non-cached mappings, since the cached one could prefetch (or speculatively load), thus creating collisions and inconsistencies. Am I wrong here ? The old hack of using non-cached mapping to avoid snoop cost in AGP and others is just that ... an ugly and horrible hacks that should have never eventuated, when the search for performance pushes HW people into utter insanity :) Cheers, Ben. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel