From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A588191F96; Wed, 3 Jul 2024 21:08:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720040914; cv=none; b=SXUvFbI7yk5r7Z6IOJ794MpNu7Y+eyOp+XgH0LxwLNEuYRYuih8WsFOy2khV+YRQt7mnDKEO7Gsm/+2FKui+k23B81g5WIw63QxXKlmq879FpcStPx+sBNyBOtjT4tYE33rX6WuUbHIU40dnfAB5lVXsbSxw6WSt60O5GOrf23w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720040914; c=relaxed/simple; bh=E6RZusLu6+EGO4OZbTy3pXuf5zwbb3APvZKN2/8n9zE=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=TqIKU5EJJh9vOUjrrm/OPkCOK74BHHBBacDWHXxvAlV5sDXkvqacwWW5B+li0NmPQnjb8z+jxw4oa4Yk1NC/90AOCNU7nwYBZmLA7vKwndytkb1+K3ZfCUtTY6VYzacAy/wrUHLvOPM+/UqutiWlqz7Vjib5ViNQfaUHJS/PuOA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KCFvnY1F; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="KCFvnY1F" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F622C2BD10; Wed, 3 Jul 2024 21:08:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1720040913; bh=E6RZusLu6+EGO4OZbTy3pXuf5zwbb3APvZKN2/8n9zE=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=KCFvnY1FCD1OA8mFJrWbd7BFdnY3e39apbo20o+IpnZ8Xmwa7zMKlUZBQR2Z9Sv6S XGdgjCpdtipMCxATZg7vtah7wpzV5/I3Y9XJy3ir2A8RKnUodEe1MfOHXduBpzQleC RnW+3cuine4AcM2aiMjgERKf+Y4LQaE4q00y8/aWG6xjeY/MPonVjDmqhKGrA44WYc 48yhSQFdTS03CsyzOopLBGLjKFvzOZhAfZb6FtlcOvdc88FLbDMDBl2unKnf4YOL5S BvuOenO4SaKFnwpigeXiDBJPUKt+xxDzbraID+CdtjKUzfO5xqP+yaa0u2MDvzHr6V jcnGR2Gsd8coQ== Date: Wed, 3 Jul 2024 16:08:31 -0500 From: Bjorn Helgaas To: Jiaxun Yang Cc: Christian =?utf-8?B?S8O2bmln?= , Icenowy Zheng , Huang Rui , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , bhelgaas@google.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: PCIe coherency in spec (was: [RFC PATCH 2/2] drm/ttm: downgrade cached to write_combined when snooping not available) Message-ID: <20240703210831.GA63958@bhelgaas> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4c5e0f77-b24d-47dd-86d2-31cb8e44b42a@app.fastmail.com> On Wed, Jul 03, 2024 at 04:52:30PM +0800, Jiaxun Yang wrote: > 在2024年7月2日七月 下午6:03，Jiaxun Yang写道： > > 在2024年7月2日七月 下午5:27，Christian König写道： > >> Am 02.07.24 um 11:06 schrieb Icenowy Zheng: > >>> [SNIP] However I don't think the definition of the AGP spec could apply on all > >>> PCI(e) implementations. The AGP spec itself don't apply on > >>> implementations that do not implement AGP (which is the most PCI(e) > >>> implementations today), and it's not in the reference list of the PCIe > >>> spec, so it does no help on this context. > >> No, exactly that is not correct. > >> > >> See as I explained the No-Snoop extension to PCIe was created to help > >> with AGP support and later merged into the base PCIe specification. > >> > >> So the AGP spec is now part of the PCIe spec. > > Hi Bjorn & linux-pci folks, > > It seems like we have some disputes on interpretation pf PCIe > specification. > > We are seeking your expertise on the question: Does PCIe > specification mandate Cache coherency via snoop? I'm not qualified to opine on this. I'd say it's a question for the PCI SIG protocol workgroup. https://forum.pcisig.com/ is a place to start. Bjorn