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[209.132.180.67]) by mx.google.com with ESMTP id c17si10666211pgl.385.2018.12.10.15.29.14; Mon, 10 Dec 2018 15:29:31 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=vS6jJnWE; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729011AbeLJUEE (ORCPT + 99 others); Mon, 10 Dec 2018 15:04:04 -0500 Received: from mail-ua1-f68.google.com ([209.85.222.68]:40004 "EHLO mail-ua1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726745AbeLJUED (ORCPT ); Mon, 10 Dec 2018 15:04:03 -0500 Received: by mail-ua1-f68.google.com with SMTP id n7so4282838uao.7 for ; Mon, 10 Dec 2018 12:04:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=AkPN93qMOA0IRtRg7BfWRUTvc7TYJd7/F0i7q7hurpE=; b=vS6jJnWEsTQW7E9sylRBX9sMMhnlc/oVluy0mVZG2Vr7PcsqeY+ug3F/fc2aIji4/S CAgVeX9SJQm8bXdentZ7Ky0exmiaiBF6SKVcRb5jYxsiVOo1TvoBmHkZzSkC6ip0pOe9 1BqM1QoTp7OEhkcRiVdkoz16B4e+Y/NWkDKqzW+ZUiw+62how8fpIEjH9CHsZi2/bkZR MpJ3hMJXywKaV+mDig7fUaZJ8+vaZ43CkkWzqBJNiJE6tNbCA0TKUOOA/N2UwqfysiD7 DTxToPS7Wo3ScROLht/BacN//iQyHZbL0MGLDF2uD8ygbad3eIz9KaAeA0LUUsppTqId n1AA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=AkPN93qMOA0IRtRg7BfWRUTvc7TYJd7/F0i7q7hurpE=; b=kJlODEYRaU89qTLzzIPZnMlIL4gheo4MdQ5jtAkd0vNstBIjEg/YZyW1QZ4Nu6vp+v 23NqG1bTXPJcDhHIrslUGJLw10a3x4mOBiSjZkgQPpMZ0cUvDC8X4IHYApnAHslIQff6 NHQop22JCwCjIA4GSv7+jlGPHrl4127bsXToswupJgeJp7+yxjUChmaZpmFDqH69J5og zCrh34ZirRU8Ls/c+ub10DI3rOtrcsxBh4wjvWa1fIncFfwsufSPBFq7yh/1d0sHwTSi L4pIk2eOQA85A77MKb65fkV0co6/NnVZjwBBvEqf5ekJ0wErPrpgjqeJaaUpH5RYCZFO 3vAA== X-Gm-Message-State: AA+aEWZxeWFf/KmLRrQmH0llbNDlUEWqxkL3VKvZqvG5vYuPHjlXWxIV lvOWHlbPAhSjcCfjPaArr9iCQEfgV5liWoZgknwo2hg9GFQM X-Received: by 2002:ab0:1058:: with SMTP id g24mr5931973uab.58.1544472241744; Mon, 10 Dec 2018 12:04:01 -0800 (PST) MIME-Version: 1.0 References: <20181130103222.GA23393@lst.de> <42b1408cafe77ebac1b1ad909db237fe34e4d177.camel@kernel.crashing.org> <20181208171746.GB15228@lst.de> <20181210193317.GA31514@lst.de> In-Reply-To: <20181210193317.GA31514@lst.de> From: Rui Salvaterra Date: Mon, 10 Dec 2018 20:03:49 +0000 Message-ID: Subject: Re: use generic DMA mapping code in powerpc V4 To: hch@lst.de Cc: benh@kernel.crashing.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 10 Dec 2018 at 19:33, Christoph Hellwig wrote: > > On Mon, Dec 10, 2018 at 05:04:46PM +0000, Rui Salvaterra wrote: > > Hi, Christoph and Ben, > > > > It just came to my mind (and this is most likely a stupid question, > > but still)=E2=80=A6 Is there any possibility of these changes having an > > (positive) effect on the long-standing problem of Power Mac machines > > with AGP graphics cards (which have to be limited to PCI transfers, > > otherwise they'll hang, due to coherence issues)? If so, I have a G4 > > machine where I'd gladly test them. > > These patches themselves are not going to affect that directly. > But IFF the problem really is that the AGP needs to be treated as not > cache coherent (I have no idea if that is true) the generic direct > mapping code has full support for a per-device coherent flag, so > support for a non-coherent AGP slot could be implemented relatively > simply. Thanks for the insight, Christoph. Well, the problem[1] is real, and it's been known for a long time, though I can't be sure if it's *only* a coherence issue. If someone who knows the hardware manages to cook up a patch (as hacky is it may be), I'll definitely fire up old my G4 laptop to test it! :) [1] https://bugs.freedesktop.org/show_bug.cgi?id=3D95017