From patchwork Thu Jun 20 12:27:25 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Cercueil X-Patchwork-Id: 13705334 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 67410C27C79 for ; Thu, 20 Jun 2024 12:28:25 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 418ED10E97B; Thu, 20 Jun 2024 12:28:24 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; unprotected) header.d=crapouillou.net header.i=@crapouillou.net header.b="znSCvmuP"; dkim-atps=neutral Received: from aposti.net (aposti.net [89.234.176.197]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5CDDD10E987 for ; Thu, 20 Jun 2024 12:28:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1718886468; 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=YPXLYwFrzAGA+us0gwq37ouAxM3z0rx257cuQIJnO9o=; b=znSCvmuPMmiK7HgZiS1dnXrJAn9HqOcXWwuDKsJyRdUHB7KlbdZnL4AqUFXZnRSheuMl2f x0POCTZ7av9s88TkeiMvXSysbDavv5TYO2WizXfmpqNroXkGKfwysl+I6BqK+k4chBj/WM kxaiN8kWUwAWNHDzBzO/jS1LImtxYLE= From: Paul Cercueil To: Jonathan Cameron , Lars-Peter Clausen , Vinod Koul , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= Cc: Jonathan Corbet , Nuno Sa , linux-iio@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Paul Cercueil Subject: [PATCH v12 6/7] Documentation: iio: Document high-speed DMABUF based API Date: Thu, 20 Jun 2024 14:27:25 +0200 Message-ID: <20240620122726.41232-7-paul@crapouillou.net> In-Reply-To: <20240620122726.41232-1-paul@crapouillou.net> References: <20240620122726.41232-1-paul@crapouillou.net> MIME-Version: 1.0 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" Document the new DMABUF based API. Signed-off-by: Paul Cercueil Co-developed-by: Nuno Sa Signed-off-by: Nuno Sa Reviewed-by: Bagas Sanjaya --- v2: - Explicitly state that the new interface is optional and is not implemented by all drivers. - The IOCTLs can now only be called on the buffer FD returned by IIO_BUFFER_GET_FD_IOCTL. - Move the page up a bit in the index since it is core stuff and not driver-specific. v3: Update the documentation to reflect the new API. v5: Use description lists for the documentation of the three new IOCTLs instead of abusing subsections. v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated index.rst whose format changed in iio/togreg. v11: - "a IIO buffer" -> "an IIO buffer" - Add variable name in IOCTL calls v12: - "obtained using..." -> "which can be obtained using..." --- Documentation/iio/iio_dmabuf_api.rst | 54 ++++++++++++++++++++++++++++ Documentation/iio/index.rst | 1 + 2 files changed, 55 insertions(+) create mode 100644 Documentation/iio/iio_dmabuf_api.rst diff --git a/Documentation/iio/iio_dmabuf_api.rst b/Documentation/iio/iio_dmabuf_api.rst new file mode 100644 index 000000000000..2836cadbd495 --- /dev/null +++ b/Documentation/iio/iio_dmabuf_api.rst @@ -0,0 +1,54 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +High-speed DMABUF interface for IIO +=================================== + +1. Overview +=========== + +The Industrial I/O subsystem supports access to buffers through a +file-based interface, with read() and write() access calls through the +IIO device's dev node. + +It additionally supports a DMABUF based interface, where the userspace +can attach DMABUF objects (externally created) to an IIO buffer, 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. + +The userspace application can also memory-map the DMABUF objects, and +access the sample data directly. The advantage of doing this vs. the +read() interface is that it avoids an extra copy of the data between the +kernel and userspace. This is particularly useful for high-speed devices +which produce several megabytes or even gigabytes of data per second. +It does however increase the userspace-kernelspace synchronization +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs have to +be used for data integrity. + +2. User API +=========== + +As part of this interface, three new IOCTLs have been added. These three +IOCTLs have to be performed on the IIO buffer's file descriptor, which +can be obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl. + + ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd)`` + Attach the DMABUF object, identified by its file descriptor, to the + IIO buffer. Returns zero on success, and a negative errno value on + error. + + ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd)`` + Detach the given DMABUF object, identified by its file descriptor, + from the IIO buffer. Returns zero on success, and a negative errno + value on error. + + Note that closing the IIO buffer's file descriptor will + automatically detach all previously attached DMABUF objects. + + ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)`` + Enqueue a previously attached DMABUF object to the buffer queue. + Enqueued DMABUFs will be read from (if output buffer) or written to + (if input buffer) as long as the buffer is enabled. diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst index 4c13bfa2865c..9cb4c50cb20d 100644 --- a/Documentation/iio/index.rst +++ b/Documentation/iio/index.rst @@ -9,6 +9,7 @@ Industrial I/O iio_configfs iio_devbuf + iio_dmabuf_api iio_tools Industrial I/O Kernel Drivers