On Mon, Nov 15, 2021 at 02:19:10PM +0000, Paul Cercueil wrote: > Hi Jonathan, > > This patchset introduces a new userspace interface based on DMABUF > objects, to complement the existing fileio based API. > > The advantage of this DMABUF based interface vs. the fileio > 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. > > The first few patches [01/15] to [03/15] are not really related, but > allow to reduce the size of the patches that introduce the new API. > > Patch [04/15] to [06/15] enables write() support to the buffer-dma > implementation of the buffer API, to continue the work done by > Mihail Chindris. > > Patches [07/15] to [12/15] introduce the new DMABUF based API. > > Patches [13/15] and [14/15] add support for cyclic buffers, only through > the new API. A cyclic buffer will be repeated on the output until the > buffer is disabled. > > Patch [15/15] adds documentation about the new API. > > For now, the API allows you to alloc DMABUF objects and mmap() them to > read or write the samples. It does not yet allow to import DMABUFs > parented to other subsystems, but that should eventually be possible > once it's wired. > > This patchset is inspired by the "mmap interface" that was previously > submitted by Alexandru Ardelean and Lars-Peter Clausen, so it would be > great if I could get a review from you guys. Alexandru's commit was > signed with his @analog.com address but he doesn't work at ADI anymore, > so I believe I'll need him to sign with a new email. Why dma-buf? dma-buf looks like something super generic and useful, until you realize that there's a metric ton of gpu/accelerator bagage piled in. So unless buffer sharing with a gpu/video/accel/whatever device is the goal here, and it's just for a convenient way to get at buffer handles, this doesn't sound like a good idea. Also if the idea is to this with gpus/accelerators then I'd really like to see the full thing, since most likely at that point you also want dma_fence. And once we talk dma_fence things get truly horrible from a locking pov :-( Or well, just highly constrained and I get to review what iio is doing with these buffers to make sure it all fits. Cheers, Daniel > > Cheers, > -Paul > > Alexandru Ardelean (1): > iio: buffer-dma: split iio_dma_buffer_fileio_free() function > > Paul Cercueil (14): > iio: buffer-dma: Get rid of incoming/outgoing queues > iio: buffer-dma: Remove unused iio_buffer_block struct > iio: buffer-dma: Use round_down() instead of rounddown() > iio: buffer-dma: Enable buffer write support > iio: buffer-dmaengine: Support specifying buffer direction > iio: buffer-dmaengine: Enable write support > iio: core: Add new DMABUF interface infrastructure > iio: buffer-dma: Use DMABUFs instead of custom solution > iio: buffer-dma: Implement new DMABUF based userspace API > iio: buffer-dma: Boost performance using write-combine cache setting > iio: buffer-dmaengine: Support new DMABUF based userspace API > iio: core: Add support for cyclic buffers > iio: buffer-dmaengine: Add support for cyclic buffers > Documentation: iio: Document high-speed DMABUF based API > > Documentation/driver-api/dma-buf.rst | 2 + > Documentation/iio/dmabuf_api.rst | 94 +++ > Documentation/iio/index.rst | 2 + > drivers/iio/adc/adi-axi-adc.c | 3 +- > drivers/iio/buffer/industrialio-buffer-dma.c | 670 ++++++++++++++---- > .../buffer/industrialio-buffer-dmaengine.c | 42 +- > drivers/iio/industrialio-buffer.c | 49 ++ > include/linux/iio/buffer-dma.h | 43 +- > include/linux/iio/buffer-dmaengine.h | 5 +- > include/linux/iio/buffer_impl.h | 8 + > include/uapi/linux/iio/buffer.h | 30 + > 11 files changed, 783 insertions(+), 165 deletions(-) > create mode 100644 Documentation/iio/dmabuf_api.rst > > -- > 2.33.0 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
