[v8,3/6] iio: core: Add new DMABUF interface infrastructure

Add the necessary infrastructure to the IIO core to support a new
optional DMABUF based interface.

With this new interface, DMABUF objects (externally created) can be
attached to a IIO buffer, and subsequently used for data transfer.

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 userful for high-speed
devices which produce several megabytes or even gigabytes of data per
second.

As part of the interface, 3 new IOCTLs have been added:

IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
 Attach the DMABUF object identified by the given file descriptor to the
 buffer.

IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
 Detach the DMABUF object identified by the given file descriptor from
 the buffer. 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 *):
 Request a data transfer to/from the given DMABUF object. Its file
 descriptor, as well as the transfer size and flags are provided in the
 "iio_dmabuf" structure.

These three IOCTLs have to be performed on the IIO buffer's file
descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v2: Only allow the new IOCTLs on the buffer FD created with
    IIO_BUFFER_GET_FD_IOCTL().

v3: - Get rid of the old IOCTLs. The IIO subsystem does not create or
    manage DMABUFs anymore, and only attaches/detaches externally
    created DMABUFs.
    - Add IIO_BUFFER_DMABUF_CYCLIC to the supported flags.

v5: - Use dev_err() instead of pr_err()
    - Inline to_iio_dma_fence()
    - Add comment to explain why we unref twice when detaching dmabuf
    - Remove TODO comment. It is actually safe to free the file's
      private data even when transfers are still pending because it
      won't be accessed.
    - Fix documentation of new fields in struct iio_buffer_access_funcs
    - iio_dma_resv_lock() does not need to be exported, make it static

v6: - Remove dead code in iio_dma_resv_lock()
    - Fix non-block actually blocking
    - Cache dma_buf_attachment instead of mapping/unmapping it for every
      transfer
    - Return -EINVAL instead of IIO_IOCTL_UNHANDLED for unknown ioctl
    - Make .block_enqueue() callback take a dma_fence pointer, which
      will be passed to iio_buffer_signal_dmabuf_done() instead of the
      dma_buf_attachment; and remove the backpointer from the priv
      structure to the dma_fence.
    - Use dma_fence_begin/end_signalling in the dma_fence critical
      sections
    - Unref dma_fence and dma_buf_attachment in worker, because they
      might try to lock the dma_resv, which would deadlock.
    - Add buffer ops to lock/unlock the queue. This is motivated by the
      fact that once the dma_fence has been installed, we cannot lock
      anything anymore - so the queue must be locked before the
      dma_fence is installed.
    - Use 'long retl' variable to handle the return value of
      dma_resv_wait_timeout()
    - Protect dmabufs list access with a mutex
    - Rework iio_buffer_find_attachment() to use the internal dmabufs
      list, instead of messing with dmabufs private data.
    - Add an atomically-increasing sequence number for fences

v8  - Fix swapped fence direction
    - Simplify fence wait mechanism
    - Remove "Buffer closed with active transfers" print, as it was dead
      code
    - Un-export iio_buffer_dmabuf_{get,put}. They are not used anywhere
      else so they can even be static.
    - Prevent attaching already-attached DMABUFs
---
 drivers/iio/industrialio-buffer.c | 462 ++++++++++++++++++++++++++++++
 include/linux/iio/buffer_impl.h   |  30 ++
 include/uapi/linux/iio/buffer.h   |  22 ++
 3 files changed, 514 insertions(+)

Message ID	20240308170046.92899-4-paul@crapouillou.net (mailing list archive)
State	Changes Requested
Headers	show 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 82A291D689; Fri, 8 Mar 2024 17:01:39 +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=1709917302; cv=none; b=nxTabBaJ6PXmyaSGasacNOAB988v0rOvPF+zfDpNiwTvxV5Z7UWB51xHyAoYd7obLaDoCcQe4NG6wAtXN87JTTBwUwznpk8R9GCBzXrz0H9jidXPxJQ9SQ3b4VG62rm6aBYtB+K8Vff+WSQges4vOgTbCkGbnRjnMWjIWIofTXk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709917302; c=relaxed/simple; bh=dW6z77dYnyuNQfWR7U3uM7QgcO6HLxlDlKFURdMB9lg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MM1BROY5oD114l/LWW8gmbJ2zPcUvNJmjD2hc9naZIjzMVwMpZ8COB+WffDV6dK35XPHzl9zAJdijY2lgnh9kwcnJPO9C41n070IFqHtnKEUzS04LgZmTrZobpVCFvxY3DIqFZXggKiBG8h4FujuVvWxj8db21zQgaRf2GBTu6Q= 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=pKelyy98; 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="pKelyy98" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1709917270; 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=D/yxylXbmYWDloiw2PSr0K04UFbHKs6qO+a5P5o+zFo=; b=pKelyy98Oy4IQx/mGav1lrm14qOzj6euecBYbJEtVUSYllP3lxWEDG9a7mZ5L8l2+/HmWB WokAtBe+bLUxAivM/izSVUSs5FxJgW7zpHaKMFa3ASDn+jkugMuxmAawR0gxqJOPPx2c3i h2qO2MjoG8VuyE/mbWoiOuor3SQbJCY= From: Paul Cercueil <paul@crapouillou.net> To: Jonathan Cameron <jic23@kernel.org>, =?utf-8?q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>, Jonathan Corbet <corbet@lwn.net>, Lars-Peter Clausen <lars@metafoo.de>, Vinod Koul <vkoul@kernel.org>, Sumit Semwal <sumit.semwal@linaro.org> Cc: Nuno Sa <nuno.sa@analog.com>, Michael Hennerich <michael.hennerich@analog.com>, 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 <paul@crapouillou.net> Subject: [PATCH v8 3/6] iio: core: Add new DMABUF interface infrastructure Date: Fri, 8 Mar 2024 18:00:43 +0100 Message-ID: <20240308170046.92899-4-paul@crapouillou.net> In-Reply-To: <20240308170046.92899-1-paul@crapouillou.net> References: <20240308170046.92899-1-paul@crapouillou.net> Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: <linux-iio.vger.kernel.org> List-Subscribe: <mailto:linux-iio+subscribe@vger.kernel.org> List-Unsubscribe: <mailto:linux-iio+unsubscribe@vger.kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit
Series	iio: new DMABUF based API \| expand [v8,0/6] iio: new DMABUF based API [v8,1/6] dmaengine: Add API function dmaengine_prep_peripheral_dma_vec() [v8,2/6] dmaengine: dma-axi-dmac: Implement device_prep_peripheral_dma_vec [v8,3/6] iio: core: Add new DMABUF interface infrastructure [v8,4/6] iio: buffer-dma: Enable support for DMABUFs [v8,5/6] iio: buffer-dmaengine: Support new DMABUF based userspace API [v8,6/6] Documentation: iio: Document high-speed DMABUF based API

[v8,3/6] iio: core: Add new DMABUF interface infrastructure

Commit Message

Comments

Patch