From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Paul Cercueil <paul@crapouillou.net>
Cc: "Jonathan Cameron" <jic23@kernel.org>,
"Michael Hennerich" <Michael.Hennerich@analog.com>,
"Lars-Peter Clausen" <lars@metafoo.de>,
"Christian König" <christian.koenig@amd.com>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Jonathan Corbet" <corbet@lwn.net>,
"Alexandru Ardelean" <ardeleanalex@gmail.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
linaro-mm-sig@lists.linaro.org,
"Linux Documentation List" <linux-doc@vger.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-iio <linux-iio@vger.kernel.org>
Subject: Re: [PATCH v2 05/12] iio: core: Add new DMABUF interface infrastructure
Date: Mon, 28 Mar 2022 23:46:02 +0300 [thread overview]
Message-ID: <CAHp75Vf8QhosJw79U97rA6u0KHY9avmzTMBUqEyWkY6jxBuPYg@mail.gmail.com> (raw)
In-Reply-To: <20220207125933.81634-6-paul@crapouillou.net>
On Tue, Feb 8, 2022 at 5:26 PM Paul Cercueil <paul@crapouillou.net> wrote:
>
> Add the necessary infrastructure to the IIO core to support a new
> optional DMABUF based interface.
>
> The advantage of this new DMABUF based interface 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
useful
> devices which produce several megabytes or even gigabytes of data per
> second.
>
> The data in this new DMABUF interface is managed at the granularity of
> DMABUF objects. Reducing the granularity from byte level to block level
> is done to reduce the userspace-kernelspace synchronization overhead
> since performing syscalls for each byte at a few Mbps is just not
> feasible.
>
> This of course leads to a slightly increased latency. For this reason an
> application can choose the size of the DMABUFs as well as how many it
> allocates. E.g. two DMABUFs would be a traditional double buffering
> scheme. But using a higher number might be necessary to avoid
> underflow/overflow situations in the presence of scheduling latencies.
>
> As part of the interface, 2 new IOCTLs have been added:
>
> IIO_BUFFER_DMABUF_ALLOC_IOCTL(struct iio_dmabuf_alloc_req *):
> Each call will allocate a new DMABUF object. The return value (if not
> a negative errno value as error) will be the file descriptor of the new
> DMABUF.
>
> IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
> Place the DMABUF object into the queue pending for hardware process.
>
> These two IOCTLs have to be performed on the IIO buffer's file
> descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
>
> To access the data stored in a block by userspace the block must be
> mapped to the process's memory. This is done by calling mmap() on the
> DMABUF's file descriptor.
>
> Before accessing the data through the map, you must use the
> DMA_BUF_IOCTL_SYNC(struct dma_buf_sync *) ioctl, with the
> DMA_BUF_SYNC_START flag, to make sure that the data is available.
> This call may block until the hardware is done with this block. Once
> you are done reading or writing the data, you must use this ioctl again
> with the DMA_BUF_SYNC_END flag, before enqueueing the DMABUF to the
> kernel's queue.
>
> If you need to know when the hardware is done with a DMABUF, you can
> poll its file descriptor for the EPOLLOUT event.
>
> Finally, to destroy a DMABUF object, simply call close() on its file
> descriptor.
...
> v2: Only allow the new IOCTLs on the buffer FD created with
> IIO_BUFFER_GET_FD_IOCTL().
Move changelogs after the cutter '--- ' line.
...
> static const struct file_operations iio_buffer_chrdev_fileops = {
> .owner = THIS_MODULE,
> .llseek = noop_llseek,
> .read = iio_buffer_read,
> .write = iio_buffer_write,
> + .unlocked_ioctl = iio_buffer_chrdev_ioctl,
> + .compat_ioctl = compat_ptr_ioctl,
Is this member always available (implying the kernel configuration)?
...
> +#define IIO_BUFFER_DMABUF_SUPPORTED_FLAGS 0x00000000
No flags available right now?
...
> + * @bytes_used: number of bytes used in this DMABUF for the data transfer.
> + * If zero, the full buffer is used.
Wouldn't be error prone to have 0 defined like this?
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2022-03-28 20:48 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 12:59 [PATCH v2 00/12] iio: buffer-dma: write() and new DMABUF based API Paul Cercueil
2022-02-07 12:59 ` [PATCH v2 01/12] iio: buffer-dma: Get rid of outgoing queue Paul Cercueil
2022-02-13 18:57 ` Jonathan Cameron
2022-02-13 19:25 ` Paul Cercueil
2022-03-28 17:17 ` Jonathan Cameron
2022-02-07 12:59 ` [PATCH v2 02/12] iio: buffer-dma: Enable buffer write support Paul Cercueil
2022-03-28 17:24 ` Jonathan Cameron
2022-03-28 18:39 ` Paul Cercueil
2022-03-29 7:11 ` Nuno Sá
2022-03-28 20:38 ` Andy Shevchenko
2022-02-07 12:59 ` [PATCH v2 03/12] iio: buffer-dmaengine: Support specifying buffer direction Paul Cercueil
2022-02-07 12:59 ` [PATCH v2 04/12] iio: buffer-dmaengine: Enable write support Paul Cercueil
2022-03-28 17:28 ` Jonathan Cameron
2022-02-07 12:59 ` [PATCH v2 05/12] iio: core: Add new DMABUF interface infrastructure Paul Cercueil
2022-03-28 17:37 ` Jonathan Cameron
2022-03-28 18:44 ` Paul Cercueil
2022-03-29 13:36 ` Jonathan Cameron
2022-03-28 20:46 ` Andy Shevchenko [this message]
2022-02-07 12:59 ` [PATCH v2 06/12] iio: buffer-dma: split iio_dma_buffer_fileio_free() function Paul Cercueil
2022-02-07 12:59 ` [PATCH v2 07/12] iio: buffer-dma: Use DMABUFs instead of custom solution Paul Cercueil
2022-03-28 17:54 ` Jonathan Cameron
2022-03-28 17:54 ` Christian König
2022-03-28 19:16 ` Paul Cercueil
2022-03-28 20:58 ` Andy Shevchenko
2022-02-07 12:59 ` [PATCH v2 08/12] iio: buffer-dma: Implement new DMABUF based userspace API Paul Cercueil
2022-02-07 12:59 ` [PATCH v2 09/12] iio: buffer-dmaengine: Support " Paul Cercueil
2022-02-07 12:59 ` [PATCH v2 10/12] iio: core: Add support for cyclic buffers Paul Cercueil
2022-02-07 13:01 ` [PATCH v2 11/12] iio: buffer-dmaengine: " Paul Cercueil
2022-02-07 13:01 ` [PATCH v2 12/12] Documentation: iio: Document high-speed DMABUF based API Paul Cercueil
2022-03-29 8:54 ` Daniel Vetter
2022-03-29 9:47 ` Paul Cercueil
2022-03-29 14:07 ` Daniel Vetter
2022-03-29 17:34 ` Paul Cercueil
2022-03-30 9:22 ` Daniel Vetter
2022-02-13 18:46 ` [PATCH v2 00/12] iio: buffer-dma: write() and new " Jonathan Cameron
2022-02-15 17:43 ` Paul Cercueil
2022-03-29 8:33 ` Daniel Vetter
2022-03-29 9:11 ` Paul Cercueil
2022-03-29 14:10 ` Daniel Vetter
2022-03-29 17:16 ` Paul Cercueil
2022-03-30 9:19 ` Daniel Vetter
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