From patchwork Mon Jan 29 17:02:01 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Cercueil X-Patchwork-Id: 13536056 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 EE05E15AAAF; Mon, 29 Jan 2024 17:03:07 +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=1706547789; cv=none; b=orjqPGhqEh/2lVXlx1AfGXGF2iklxejE25phoBnmskr9snv6i3rXvTJCwjNX5saVBK87Zpgale5/dKAlzge6GJO7xFcPzbBgd6s17gnnlKygceC9DEAjjJZQcyZrMY3/BZqoSkdWflXj4a4dvMAyHUT9VJSLW3DNqDNXWWQpCMI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706547789; c=relaxed/simple; bh=wHWg4LZRwCfhResqeH0XOYfyJt+0f2JWYpJlo3R3dtA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Rp2Onbvusjs830PS7Va0/UJ9zo+zfjboyQVxb49f5ebChjPapgTpAQ8zb8uSa8yhBTYfHVfkJRN9Ck5OD0GZljRq5k7NMXYor2+bxyC3Q/OqWPiNo/aqO7KJTQQEUtSFazTiJwThK7DOvA8FhwS/LKA0eY3WkqZ+LsI6NjhO30g= 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=Hz5iSkzr; 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="Hz5iSkzr" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1706547741; 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=6SosLHUfbvBusyQrjhEdH6qlujZTce4ql106/+fLWzw=; b=Hz5iSkzreG374dszhrBcWBdOw/8E9kBUgkLUyYVVOzM0dIA3qjeGkDueAhT1yesWaD3R/J CU0Dav7pa+LPws6gK3o25zLvdwVZOMMblQ+ZLMEMbNg+y0SSabHObT9U9BAeFIJSWcS+Ht 4Mel07g7k6sXDOVHXLU9KIMPE1H9a9U= From: Paul Cercueil To: Jonathan Cameron , Jonathan Corbet , Lars-Peter Clausen , Vinod Koul , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= Cc: Daniel Vetter , Nuno Sa , Michael Hennerich , linux-doc@vger.kernel.org, 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 Subject: [PATCH v6 6/6] Documentation: iio: Document high-speed DMABUF based API Date: Mon, 29 Jan 2024 18:02:01 +0100 Message-ID: <20240129170201.133785-7-paul@crapouillou.net> In-Reply-To: <20240129170201.133785-1-paul@crapouillou.net> References: <20240129170201.133785-1-paul@crapouillou.net> Precedence: bulk X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Document the new DMABUF based API. Signed-off-by: Paul Cercueil --- 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. --- Documentation/iio/dmabuf_api.rst | 54 ++++++++++++++++++++++++++++++++ Documentation/iio/index.rst | 2 ++ 2 files changed, 56 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..1cd6cd51a582 --- /dev/null +++ b/Documentation/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 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