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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0E3A4CA5FFF for ; Wed, 7 Oct 2026 20:13:01 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 72F2910E3A0; Wed, 7 Oct 2026 20:13:00 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="Z4sH8l8a"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6C07510E3A0 for ; Wed, 7 Oct 2026 20:12:59 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 1C7A94165D; Wed, 7 Oct 2026 20:12:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CAD001F000FF; Wed, 7 Oct 2026 20:12:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791403979; bh=NkhqUzzdxA0MVE0meZ2UnW8jxa68cZXpUz1Q9eXyAVQ=; h=Date:From:To:Cc:Subject:In-Reply-To; b=Z4sH8l8au7rGkzWgZQzY7oN5d+6g+awV127IUsOmiofzHPw2d3iZ4uPMJY0ZR+ilZ KoqFKDy6I9mWc06+H/S5jL+G7NcSrNrgCT385iZzEM4aEXpENT0xRtSodXm5kn8cDF IJLMwndnxchJxpYZV1jXq7V+4WjXZ3drM6mjQY3hKen/J4KSd+2+BiMdzrC22eP7t1 QrjHTrHcI2/t54yHDyOfwQeglJPjDztuv7yrGkeicH55awtbPQ8zKvIYBpQipXOnZk R93AdEVQimgazo0I0LWZRqMepJkV8aHibBQ08MFSJhA6ADdwes553hftiSxnRnYfw7 fuIlJ781os/Sw== Date: Wed, 7 Oct 2026 15:12:57 -0500 From: Bjorn Helgaas To: Leon Romanovsky Cc: Bjorn Helgaas , Logan Gunthorpe , Jason Gunthorpe , "Joerg Roedel (AMD)" , Will Deacon , Robin Murphy , Christian =?utf-8?B?S8O2bmln?= , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, iommu@lists.linux.dev, Tushar Dave , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-rdma@vger.kernel.org, kvm@vger.kernel.org, Chaitanya Kulkarni , Greg Kroah-Hartman , Jens Axboe , Alex Williamson , Ankit Agrawal , Jonathan Corbet , Shuah Khan , Randy Dunlap , Sumit Semwal Subject: Re: [PATCH v9 01/18] PCI/P2PDMA: Document the TLP attribute assumptions Message-ID: <20261007201257.GA781492@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261001-fix-p2p-acs-v4-0-v9-1-1a8e0f50ddd9@nvidia.com> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Thu, Oct 01, 2026 at 02:55:09PM +0300, Leon Romanovsky wrote: > From: Leon Romanovsky > > P2PDMA selects a mapping without receiving the Request's ordering or > Address Type attributes. Its ACS handles only strictly ordered Requests > carrying an Untranslated address. > > Document that the result is not defined for Relaxed Ordering or > ATS-translated Requests because those TLP attributes can select different > routes through the fabric. > > Reviewed-by: Logan Gunthorpe > Tested-by: Tushar Dave > Signed-off-by: Leon Romanovsky > --- > Documentation/driver-api/pci/p2pdma.rst | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/Documentation/driver-api/pci/p2pdma.rst b/Documentation/driver-api/pci/p2pdma.rst > index 63cff9e4d2c9..80f8fec9b0e9 100644 > --- a/Documentation/driver-api/pci/p2pdma.rst > +++ b/Documentation/driver-api/pci/p2pdma.rst > @@ -15,6 +15,13 @@ then based on the ACS settings the transaction can route entirely within > the PCIe hierarchy and never reach the root port. The kernel will evaluate > the PCIe topology and always permit P2P in these well-defined cases. > > +This evaluation assumes clients issue strictly ordered Requests carrying an > +Untranslated address. Its result is not defined when clients use Relaxed > +Ordering or issue ATS-translated Requests because those TLP attributes can > +select different routes through the fabric. Unless ACS Translation Blocking > +is enabled, a Port with ACS Direct Translated P2P enabled routes a > +Translated Request directly to the peer regardless of the redirect controls. This whole paragraph is removed later in the series, so kudos for documenting the current state before it changes :) Unrelated to anything in this series, but this doc mentions "p2p_provider", which doesn't exist. Should it be "p2pdma_provider"?