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[209.132.180.67]) by mx.google.com with ESMTP id x64si12596440pfb.120.2018.12.11.01.38.12; Tue, 11 Dec 2018 01:38:28 -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=ETMPSNBl; 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 S1726226AbeLKJhP (ORCPT + 99 others); Tue, 11 Dec 2018 04:37:15 -0500 Received: from mail-ua1-f51.google.com ([209.85.222.51]:42394 "EHLO mail-ua1-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726104AbeLKJhP (ORCPT ); Tue, 11 Dec 2018 04:37:15 -0500 Received: by mail-ua1-f51.google.com with SMTP id d21so4890086uap.9 for ; Tue, 11 Dec 2018 01:37:14 -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=bfu37XvicU8GOJunSNdquvYomfpuT3hN3SAggWjLB98=; b=ETMPSNBlvml7wFYO6tgjpExr0YIg9GL5/413ehIRg5zTej2kkpqA1na2u0J/dUQe7Y 59tT99eFM7+fkYqlCA4iESfs4p+QpkfFZ8Cvkwgt/oZmR70uOEeKDK4wPar7L7IzmY4V asl7P05TB7XkwrbkNjVt+qGlO64b4M+ul90VC5iSZe+kG+GmHGLy/FdGCxTCB7GWhX7a yEnAZqM3S0OpSDXLflcsSQdkyjDiUayZnwJjiqiacqknrN3DOCMEplmCQ+F+M4QL8w07 w+RGWCskK9DKp/aVZwUnFQpvjtY/xrJbBwLyN7I8tDsxraq1l8BDNc8DblSeeNW/89it fIoQ== 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=bfu37XvicU8GOJunSNdquvYomfpuT3hN3SAggWjLB98=; b=FpcIXz/Lpet7t4g1ZHi3AJL7cbAWz2VAD0JrsqxSCmTCacQnStb7eYtO0el0zQs80h tRmm6cqnkpPWGjUR/LFORDwRXKhhIkFRANuyGBMivhRFfy6lnU5CibEn9Q74iratAIiM 70C3jWyOo114ChUFzWiCIKhiPPUH4C3tvefSkFBoT71ZyN4fhTene0U+VWA/IgFo8XPl Ky8Ll+RBS7j26uSss+zotcFaYPkyWIRkRU0i1hFr4AOyLMXAW53nPIZ1YDDFAdW216Fc kDJWS9eATLXl3Hyu+ioDoJmPnXKgsCarkd6fQLucOasCb3/v5y9Sf2HdPk82tfc0UMdQ oJCA== X-Gm-Message-State: AA+aEWYKj4FnirYxa2CYa8lQSw0YqRj9ALA1h+KfqqtZEEMB5FLSwr+u aNNEPduQ5OXiG7Y3MD5seu2+H+MOBWH2R/UhTbURVJtO0g== X-Received: by 2002:ab0:14f2:: with SMTP id f47mr6817465uae.27.1544521033581; Tue, 11 Dec 2018 01:37:13 -0800 (PST) MIME-Version: 1.0 References: <20181130103222.GA23393@lst.de> <42b1408cafe77ebac1b1ad909db237fe34e4d177.camel@kernel.crashing.org> <20181208171746.GB15228@lst.de> <20181210193317.GA31514@lst.de> <8a2e104a6c5b745adca8e7f3310af564f3b8a75d.camel@kernel.crashing.org> In-Reply-To: <8a2e104a6c5b745adca8e7f3310af564f3b8a75d.camel@kernel.crashing.org> From: Rui Salvaterra Date: Tue, 11 Dec 2018 09:37:02 +0000 Message-ID: Subject: Re: use generic DMA mapping code in powerpc V4 To: benh@kernel.crashing.org Cc: hch@lst.de, 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 20:49, Benjamin Herrenschmidt wrote: > [snip] > > AGP is a gigantic nightmare :-) It's not just cache coherency issues > (some implementations are coherent, some aren't, Apple's is ... weird). > > Apple has all sort of bugs, and Darwin source code only sheds light on > some of them. Some implementation can only read, not write I think, for > example. There are issues with transfers crossing some boundaries I > beleive, but it's all unclear. > > Apple makes this work with a combination of hacks in the AGP "driver" > and the closed source GPU driver, which we don't see. > > I have given up trying to make that stuff work reliably a decade ago :) > > Cheers, > Ben. That's what I was afraid of=E2=80=A6 what a mess. At least now I have a definitive answer from one of the original authors of the code, thanks a lot, Ben. :) I have an unresearched belief that AGP support was hacked in the Mac series as an afterthought (weren't they supposed to be PCI/PCI-X only?), and your explanation surely seems to corroborate. :/