Hi Jonathan,
This is the v6 of my patchset that introduces a new interface based on DMABUF objects.
The code was updated quite a bit, using the feedback on the list for this patchset but also the feedback I received on the FunctionFS patchset that I'm working on upstreaming in parallel [1] where the DMABUF handling code is very similar.
See below for the full changelog.
I decided to drop the scope-based memory management for dma_buf and I hope you are OK with that. Christian wants the patch(es) to support scope-based memory management in dma-buf as a separate patchset; once it's in, I will gladly send a follow-up patch to use __free() where it makes sense.
For performance numbers, I'll point you to the cover letter for my v5 patchset [2].
This patchset was based on next-20240129.
Cheers, -Paul
[1] https://lore.kernel.org/all/20230322092118.9213-1-paul@crapouillou.net/ [2] https://lore.kernel.org/linux-iio/219abc43b4fdd4a13b307ed2efaa0e6869e68e3f.c...
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Changelog: * [2/6]: - Use new prototype for axi_dmac_alloc_desc() as it changed upstream * [3/6]: - 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 * [4/6]: - Update iio_dma_buffer_enqueue_dmabuf() to take a dma_fence pointer - Pass that dma_fence pointer along to iio_buffer_signal_dmabuf_done() - Add iio_dma_buffer_lock_queue() / iio_dma_buffer_unlock_queue() - Do not lock the queue in iio_dma_buffer_enqueue_dmabuf(). The caller will ensure that it has been locked already. - Replace "int += bool;" by "if (bool) int++;" - Use dma_fence_begin/end_signalling in the dma_fence critical sections - Use one "num_dmabufs" fields instead of one "num_blocks" and one "num_fileio_blocks". Make it an atomic_t, which makes it possible to decrement it atomically in iio_buffer_block_release() without having to lock the queue mutex; and in turn, it means that we don't need to use iio_buffer_block_put_atomic() everywhere to avoid locking the queue mutex twice. - Use cleanup.h guard(mutex) when possible - Explicitely list all states in the switch in iio_dma_can_enqueue_block() - Rename iio_dma_buffer_fileio_mode() to iio_dma_buffer_can_use_fileio(), and add a comment explaining why it cannot race vs. DMABUF. * [5/6]: - Populate .lock_queue / .unlock_queue callbacks - Switch to atomic memory allocations in .submit_queue, because of the dma_fence critical section - Make sure that the size of the scatterlist is enough
--- Paul Cercueil (6): dmaengine: Add API function dmaengine_prep_slave_dma_vec() dmaengine: dma-axi-dmac: Implement device_prep_slave_dma_vec iio: core: Add new DMABUF interface infrastructure iio: buffer-dma: Enable support for DMABUFs iio: buffer-dmaengine: Support new DMABUF based userspace API Documentation: iio: Document high-speed DMABUF based API
Documentation/iio/dmabuf_api.rst | 54 ++ Documentation/iio/index.rst | 2 + drivers/dma/dma-axi-dmac.c | 40 ++ drivers/iio/buffer/industrialio-buffer-dma.c | 181 ++++++- .../buffer/industrialio-buffer-dmaengine.c | 58 ++- drivers/iio/industrialio-buffer.c | 462 ++++++++++++++++++ include/linux/dmaengine.h | 25 + include/linux/iio/buffer-dma.h | 31 ++ include/linux/iio/buffer_impl.h | 33 ++ include/uapi/linux/iio/buffer.h | 22 + 10 files changed, 891 insertions(+), 17 deletions(-) create mode 100644 Documentation/iio/dmabuf_api.rst