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dkim=none (message not signed) header.d=none;dmarc=fail action=none header.from=foss.st.com; Received-SPF: Fail (protection.outlook.com: domain of foss.st.com does not designate 164.130.1.87 as permitted sender) receiver=protection.outlook.com; client-ip=164.130.1.87; helo=smtpO365.st.com; Received: from smtpO365.st.com (164.130.1.87) by AMS0EPF000001B1.mail.protection.outlook.com (10.167.16.165) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.382.8 via Frontend Transport; Tue, 1 Sep 2026 12:56:24 +0000 Received: from ENXDAG1NODE4.st.com (10.75.129.197) by smtpo365.st.com (10.250.44.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.43; Tue, 1 Sep 2026 14:58:21 +0200 Received: from [10.48.87.127] (10.48.87.127) by ENXDAG1NODE4.st.com (10.75.129.197) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.43; Tue, 1 Sep 2026 14:56:23 +0200 Message-ID: <720d36e8-df57-41fc-9764-ce66addc066e@foss.st.com> Date: Tue, 1 Sep 2026 14:56:21 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 4/5] docs: rpmsg: add virtio config space details To: Tanmay Shah , , , , CC: , , References: <20260828145853.2843486-1-tanmay.shah@amd.com> <20260828145853.2843486-5-tanmay.shah@amd.com> Content-Language: en-US From: Arnaud POULIQUEN In-Reply-To: <20260828145853.2843486-5-tanmay.shah@amd.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 50A8Lr3pX2jhAYZm3C7I58Kh5NM5UHiFTIU7czvtuzla2y4hyqq+iJoZrqCJhKouN6em+jlal6bkA1T91LeyuncLcsSpsm8WpHo9mWH+FPkpTG91ac8emeGsinT2fKpVyNFH4y/T3SCppFYwv4zIm+0JBrbAKy0jFPtLXgZw+26kC23l+on0rsI01+Zgs1xYQshZkkqNxTHXXEEsOY3rp0Rct3+mLRJgnq0VbG7ux5hYysiPS29lQuXLdaRSaWWupspTnfMse7H61Ch1P1paFbAZiab2Pm4k70lNwaP64vd9ZHmP4wp/smGzMoo8QzHq3W08+48rOkNgqcM3LyfKWGzbtFs0fEB2Yx8MI6adQPwvdQ2qjUZjtxMHBXpOjfXx4NPkwxPYbpwG+GbQ57KG86BermUughMfofU6fFirh0kBZ6M5AUdK5Mta8drXLN4q X-OriginatorOrg: foss.st.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Sep 2026 12:56:24.4788 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b1ecbb75-76be-4a2f-ab58-08df08286de9 X-MS-Exchange-CrossTenant-Id: 75e027c9-20d5-47d5-b82f-77d7cd041e8f X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=75e027c9-20d5-47d5-b82f-77d7cd041e8f;Ip=[164.130.1.87];Helo=[smtpO365.st.com] X-MS-Exchange-CrossTenant-AuthSource: AMS0EPF000001B1.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR10MB6388 On 8/28/26 16:58, Tanmay Shah wrote: > The virtio config space can provide single rpmsg buffer size in each > direction. Document details of the configurable buffer size via virtio > config space. > > Signed-off-by: Tanmay Shah > --- > > Changes in v8: > - "%s/or differnt RX and TX sizes)/or different RX and TX queue sizes)/" > > Changes in v6: > - rpmsg.rst: modify alignment related documentation > > Changes in v5: > - fix documentation of buffer alignment > > Documentation/staging/rpmsg.rst | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/Documentation/staging/rpmsg.rst b/Documentation/staging/rpmsg.rst > index 63612b7ee120..d711d1643bab 100644 > --- a/Documentation/staging/rpmsg.rst > +++ b/Documentation/staging/rpmsg.rst > @@ -299,3 +299,20 @@ by the bus, and can then start sending messages to the remote service. > > The plan is also to add static creation of rpmsg channels via the virtio > config space, but it's not implemented yet. > + > +Configurable buffer sizes > +========================= > + > +By default each rpmsg buffer is 512 bytes, and the same size is used for both > +the receive and transmit directions. Remote processors that need a different > +size (for example a larger MTU, or different RX and TX queue sizes) can > +advertise it through the virtio device config space by setting the > +VIRTIO_RPMSG_F_BUFSZ feature bit. > + > +When this feature is negotiated, the driver reads struct virtio_rpmsg_config > +from the config space. This structure provides the size of a single buffer for > +each direction (TX and RX). The device should advertise TX/RX buffer sizes > +that already satisfy its own alignment constraints. Nitpicking: following sentence seems to me more explicit as the alignment concerns the buffer address. It is only a suggestion The device should advertise TX/RX buffer sizes that already satisfy the alignment constraints of its buffers. Thanks, Arnaud > + > +If the feature is not negotiated, the default 512-byte buffers are used for > +both directions.