From patchwork Wed Jan 17 12:26:46 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Cercueil X-Patchwork-Id: 13521670 Received: from aposti.net (aposti.net [89.234.176.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B3840200D9; Wed, 17 Jan 2024 12:27:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=89.234.176.197 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705494449; cv=none; b=cvVJnvPyIggL1ePe1Dxm2Ck/sL93g/J417S3ZfHBqgMTkvWIL/kI9B9xVzWIo+G/A29yT9Dbmca2oVye22aERJ4n6aOqOmfp6Ohd6Kbo1NyX8v4JnGVKrCJInHyxBrVOZpE99qf1JwZLkqUfTevrZBLQFmwD+dTNWaKv4TkefsE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705494449; c=relaxed/simple; bh=cJbgWol1KPqWfYEC1f0fo3P+Gvr3uUpwLWEV8WXaueM=; h=DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:In-Reply-To: References:MIME-Version:Content-Transfer-Encoding:X-Spam; b=Gb3mn5ZWsD6UqqZGxUScc/DmdAmA9YoXPLYs/PsTIcI2ZGevJzK5JdxwhQb4Jpy+vd2OZjMhxLbTtzfukJRZVIcqrZ44A8hmAeZ2hNoIAe5XnPQVMIlyKM7/sGBEmMdTP5YimDEI11tw4n7jeQKcM3ZYutGQOijOUzxU+VNP2zw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=crapouillou.net; spf=pass smtp.mailfrom=crapouillou.net; dkim=pass (1024-bit key) header.d=crapouillou.net header.i=@crapouillou.net header.b=r779x7mk; arc=none smtp.client-ip=89.234.176.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=crapouillou.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=crapouillou.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=crapouillou.net header.i=@crapouillou.net header.b="r779x7mk" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1705494415; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zL3Tp6j0FI2WH0LNy5N+K5/yV+yjLiDhRH8Apc3kyR0=; b=r779x7mkgifHJMN6ShIX7jeNnvVGK0qxFXSIORj1ezPRQH3QT8H7kkaH2RvoSB3uULlm4u 3jbtB/thCBhngkDbpQM6jMgmXDO7BGFfxMPUGf0jX/gTjCDgcj+CXtfNgfwc7Vigz8aFuE OofQGjqzjXAa2mfCrHjY5ykmLYedP+c= From: Paul Cercueil To: Greg Kroah-Hartman , Jonathan Corbet , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= Cc: Jonathan Cameron , =?utf-8?q?Nuno_S=C3=A1?= , Michael Hennerich , linux-usb@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Paul Cercueil Subject: [PATCH v4 4/4] Documentation: usb: Document FunctionFS DMABUF API Date: Wed, 17 Jan 2024 13:26:46 +0100 Message-ID: <20240117122646.41616-5-paul@crapouillou.net> In-Reply-To: <20240117122646.41616-1-paul@crapouillou.net> References: <20240117122646.41616-1-paul@crapouillou.net> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Spam: Yes Add documentation for the three ioctls used to attach or detach externally-created DMABUFs, and to request transfers from/to previously attached DMABUFs. Signed-off-by: Paul Cercueil --- v3: New patch --- Documentation/usb/functionfs.rst | 36 ++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/Documentation/usb/functionfs.rst b/Documentation/usb/functionfs.rst index a3054bea38f3..d05a775bc45b 100644 --- a/Documentation/usb/functionfs.rst +++ b/Documentation/usb/functionfs.rst @@ -2,6 +2,9 @@ How FunctionFS works ==================== +Overview +======== + From kernel point of view it is just a composite function with some unique behaviour. It may be added to an USB configuration only after the user space driver has registered by writing descriptors and @@ -66,3 +69,36 @@ have been written to their ep0's. Conversely, the gadget is unregistered after the first USB function closes its endpoints. + +DMABUF interface +================ + +FunctionFS additionally supports a DMABUF based interface, where the +userspace can attach DMABUF objects (externally created) to an endpoint, +and subsequently use them for data transfers. + +A userspace application can then use this interface to share DMABUF +objects between several interfaces, allowing it to transfer data in a +zero-copy fashion, for instance between IIO and the USB stack. + +As part of this interface, three new IOCTLs have been added. These three +IOCTLs have to be performed on a data endpoint (ie. not ep0). They are: + + ``FUNCTIONFS_DMABUF_ATTACH(int)`` + Attach the DMABUF object, identified by its file descriptor, to the + data endpoint. Returns zero on success, and a negative errno value + on error. + + ``FUNCTIONFS_DMABUF_DETACH(int)`` + Detach the given DMABUF object, identified by its file descriptor, + from the data endpoint. Returns zero on success, and a negative + errno value on error. Note that closing the endpoint's file + descriptor will automatically detach all attached DMABUFs. + + ``FUNCTIONFS_DMABUF_TRANSFER(struct usb_ffs_dmabuf_transfer_req *)`` + Enqueue the previously attached DMABUF to the transfer queue. + The argument is a structure that packs the DMABUF's file descriptor, + the size in bytes to transfer (which should generally correspond to + the size of the DMABUF), and a 'flags' field which is unused + for now. Returns zero on success, and a negative errno value on + error.