From patchwork Mon Apr 3 15:49:55 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Cercueil X-Patchwork-Id: 13198384 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4DECBC76196 for ; Mon, 3 Apr 2023 15:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232812AbjDCP5j (ORCPT ); Mon, 3 Apr 2023 11:57:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232932AbjDCP5Z (ORCPT ); Mon, 3 Apr 2023 11:57:25 -0400 Received: from aposti.net (aposti.net [89.234.176.197]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC66C448E; Mon, 3 Apr 2023 08:56:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1680537006; 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=WQ7k7KsV39QPGYjokDQtx5Buy0HkE7q//zbkWOqAhK8=; b=DEzFQ5dHQ52MTjpnNy7RIpuyYfglVdd9G+QCmQAVvx+THx1Dg3RcG9JdnozS0UiT+lI+RR CwJVsJsAsQoVJKd/Og7/j2Tt0PnG/Sny+C9Ea9H9gfozB95dYUVccWs0aEeC/OjeWUzyfq tjjtxRST8Z3B0Ek776+YV19sFnLRNGg= From: Paul Cercueil To: Jonathan Cameron , Lars-Peter Clausen , Vinod Koul , Michael Hennerich , =?utf-8?q?Nuno_S=C3=A1?= , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= Cc: linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, linux-iio@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Paul Cercueil , Jonathan Corbet , linux-doc@vger.kernel.org Subject: [PATCH v3 11/11] Documentation: iio: Document high-speed DMABUF based API Date: Mon, 3 Apr 2023 17:49:55 +0200 Message-Id: <20230403154955.216148-2-paul@crapouillou.net> In-Reply-To: <20230403154955.216148-1-paul@crapouillou.net> References: <20230403154800.215924-1-paul@crapouillou.net> <20230403154955.216148-1-paul@crapouillou.net> MIME-Version: 1.0 X-Spam: Yes Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org Document the new DMABUF based API. Signed-off-by: Paul Cercueil Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org --- 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. --- Documentation/iio/dmabuf_api.rst | 59 ++++++++++++++++++++++++++++++++ Documentation/iio/index.rst | 2 ++ 2 files changed, 61 insertions(+) create mode 100644 Documentation/iio/dmabuf_api.rst diff --git a/Documentation/iio/dmabuf_api.rst b/Documentation/iio/dmabuf_api.rst new file mode 100644 index 000000000000..4d70372c7ebd --- /dev/null +++ b/Documentation/iio/dmabuf_api.rst @@ -0,0 +1,59 @@ +.. 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 a 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, +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl. + +``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)`` +---------------------------------------------------------------- + +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)`` +-------------------------------------------------------- + +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 1b7292c58cd0..3eae8fcb1938 100644 --- a/Documentation/iio/index.rst +++ b/Documentation/iio/index.rst @@ -9,6 +9,8 @@ Industrial I/O iio_configfs + dmabuf_api + ep93xx_adc bno055