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From:   Alexandru Ardelean <ardeleanalex@gmail.com>
Date:   Mon, 15 Feb 2021 16:10:45 +0200
Message-ID: <CA+U=DsryDk+91F3bfL-vXhqwEqw7yF-po2A4BXwkzKYy2352WQ@mail.gmail.com>
Subject: Re: [PATCH v6 00/24] iio: core,buffer: add support for multiple IIO
 buffers per IIO device
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Alexandru Ardelean <alexandru.ardelean@analog.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-iio <linux-iio@vger.kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        "Hennerich, Michael" <Michael.Hennerich@analog.com>,
        =?UTF-8?B?TnVubyBTw6E=?= <nuno.sa@analog.com>,
        "Bogdan, Dragos" <dragos.bogdan@analog.com>
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On Mon, Feb 15, 2021 at 3:59 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Mon, 15 Feb 2021 12:40:19 +0200
> Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
>
> Hi Alex,
>
> One thought on this that came up whilst reading through it again.
> There are several uses for multiple buffers.
> 1) input vs output buffers
> 2) A device with separately clocked sampling of different channels.

So, ADI typically has use-cases for 1).
Mostly RF transceivers.
Traditionally, these were written (inside the ADI tree) as 2-3 IIO
devices (1 IIO device for each path,1 for TX and 1-2 for RX).
With multi-buffer, they can be a single IIO device with 2-3 IIO buffers.

There are some ADI devices that have channels that can run at different speeds.
But this hasn't been an important use-cases to deal with.
Typically, a common-rate would be picked [for all channels] and that's that.
I think some people find this per-channel rates interesting; but let's see.

>
> For case 2, there is at least sometimes a trigger involved
> (often data ready) so we probably also need to think long term about how
> to support multiple current_triggers in one driver.
>
> I guess that's something for us to figure out when we need it however.
>
> Thanks for you hard work on finally getting this upstream.
> + Lars (and maybe others) for earlier work on this.

Thank you as well.

>
> Whilst I've applied all these, they are only exposed in the testing branch
> of iio.git on kernel.org so far and as such any additional review anyone
> else wants to give would be welcome!

I feel there may be other users stumbling over this multibuffer
support, and try it out.
Often people don't seem to care about multibuffer, until they really need it.
A bit of chicken-n-egg problem.
But after being added, people may see it and start to use it.

>
> Jonathan
>
> > Changelog v5 -> v6:
> > * https://lore.kernel.org/linux-iio/20210211122452.78106-1-alexandru.ardelean@analog.com/T/#t
> > * merged series 'iio: kfifo: define a devm_iio_kfifo_buffer_setup helper' into this
> >    https://lore.kernel.org/linux-iio/20210214143313.67202-4-alexandru.ardelean@analog.com/T/#u
> > * merged patch 'iio: buffer-dma,adi-axi-adc: introduce devm_iio_dmaengine_buffer_setup()' into this
> >    https://lore.kernel.org/linux-iio/20210214155817.68678-1-alexandru.ardelean@analog.com/T/#u
> > * patch 'iio: core: wrap iio device & buffer into struct for character devices'
> >    - moved kfree(ib) to be first in iio_chrdev_release() to make the cleanup
> >      order be reversed as the open() order
> > * patch 'iio: buffer: group attr count and attr alloc'
> >    - sizeof(struct attribute *)  ->   sizeof(*attr)  in kcalloc()
> > * patch 'iio: core: merge buffer/ & scan_elements/ attributes'
> >    - minor rework in iio_buffer_register_legacy_sysfs_groups() to
> >      use more 'sizeof(*attrs)' in allocations
> >    - fixed typo 'legacy_buffer_el_group' -> 'legacy_buffer_group'
> >    - updated comment about
> >      '/* we only need to link the legacy buffer groups for the first buffer */'
> >      to
> >      '/* we only need to register the legacy groups for the first buffer */'
> > * patch 'iio: buffer: add ioctl() to support opening extra buffers for IIO device'
> >    - removed 'buf_name' from iio_device_buffer_getfd();
> >       passing "iio:buffer" name; since it should be a class-name
> >    - removed extra-line in drivers/iio/industrial-core.c
> >    -  changed init order in iio_device_buffer_getfd() and matched it with reverse in
> >       iio_buffer_chrdev_release()
> >    - calling put_unused_fd() in iio_device_buffer_getfd() if copy_to_user() fails
> > * added 'iio: dummy: iio_simple_dummy_buffer: use triggered buffer core calls'
> > * patch ' iio: buffer: introduce support for attaching more IIO buffers'
> >    - now handling iio_device_attach_buffer() error returns
> >    - rename iio_buffer_free_sysfs_and_mask() -> iio_buffers_free_sysfs_and_mask()
> >    - rename iio_buffer_alloc_sysfs_and_mask() -> iio_buffer_alloc_sysfs_and_mask()
> > * patch 'tools: iio: convert iio_generic_buffer to use new IIO buffer API'
> >   - removed extra close() if getfd() ioctl() errors out
> >   - added comment that the sanity check for buffer0 should not be done
> >     under normal operation
> >   - update message from
> >    "This device does not support buffers"
> >    to
> >    "Device does not have this many buffers"
> >
> > Changelog v4 -> v5:
> > * https://lore.kernel.org/linux-iio/20210210100823.46780-1-alexandru.ardelean@analog.com/T/#t
> > * patch 'iio: buffer: add ioctl() to support opening extra buffers for IIO device'
> >   don't return -EBUSY in iio_buffer_poll_wrapper(); return 0
> >   __poll_t is unsigned, so returning 0 is the best we can do
> >   Reported-by: kernel test robot <lkp@intel.com>
> > * patch 'iio: buffer: dmaengine: obtain buffer object from attribute'
> >   removed unused 'indio_dev' variable; seems i missed this initially
> > * patch 'iio: buffer: add ioctl() to support opening extra buffers for IIO device'
> >   call 'wake_up(buffer->pollq)' in iio_buffer_chrdev_release()
> >
> > Changelog v3 -> v4:
> > * https://lore.kernel.org/linux-iio/20210201145105.20459-1-alexandru.ardelean@analog.com/
> > * patch 'docs: ioctl-number.rst: reserve IIO subsystem ioctl() space'
> >    remove 'uapi/' from `uapi/linux/iio/*.h`
> > * patch 'iio: core: register chardev only if needed'
> >    add commit comment about potentially breaking userspace ABI with chardev removal
> > * patch 'iio: core: rework iio device group creation'
> >    remove NULL re-init in iio_device_unregister_sysfs() ; memory is being free'd
> > * patch 'iio: buffer: group attr count and attr alloc'
> >   extend commit comment about the 2 or 1 buffer directores
> > * patch 'iio: core: merge buffer/ & scan_elements/ attributes'
> >    fixed static checker complaints
> >     - removed unused global
> >     - initialize omitted 'ret = -ENOMEM' on error path
> >     - made iio_buffer_unregister_legacy_sysfs_groups() static
> > * patch 'iio: buffer: wrap all buffer attributes into iio_dev_attr'
> >    - update some omitted unwindings; seems i forgot a few originally
> >      this was showing up when trying to read from buffer1
> > * add patch 'iio: buffer: move __iio_buffer_free_sysfs_and_mask() before alloc func'
> > * patch 'iio: buffer: introduce support for attaching more IIO buffers'
> >    - removed 'iio_dev_opaque->attached_buffers = NULL' after kfree()
> >    - using 'iio_dev_opaque->attached_buffers_cnt' to check that we have buffers
> >       instead of checking 'indio_dev->buffer'
> > * patch 'iio: buffer: add ioctl() to support opening extra buffers for IIO device'
> >    - replaced -ENOENT with -ENODEV when buffer index is out of range
> > * add 'iio: core: rename 'dev' -> 'indio_dev' in iio_device_alloc()'
> > * add 'iio: buffer: dmaengine: obtain buffer object from attribute'
> > * add tools/iio patches for new multibuffer logic
> >    tools: iio: make iioutils_get_type() private in iio_utils
> >    tools: iio: privatize globals and functions in iio_generic_buffer.c file
> >    tools: iio: convert iio_generic_buffer to use new IIO buffer API
> >
> > Changelog v2 -> v3:
> > * https://lore.kernel.org/linux-iio/20210122155805.83012-1-alexandru.ardelean@analog.com/
> > * added commit 'docs: ioctl-number.rst: reserve IIO subsystem ioctl() space'
> >   reserving 'i' 0x90-0x9F ioctls for IIO
> >   I did not see any conflicts with others (in the doc)
> >   - related to this, the new IIO_BUFFER_GET_FD_IOCTL is now at 'i' 0x91
> > * changed approach for creating sysfs buffer directories;
> >   - they are now created as groups on the IIO device; that also means
> >     that the groups array needs to be krealloc-ed and assign later in
> >     the registration
> >   - merged bufferX/ and scan_elementsX/ directories into a single
> >     bufferX/ directory
> >   - for legacy the buffer/ & scan_elements/ directories are kept; but
> >     they're groups objects have been moved on the iio_dev_opaque object
> >   - internally, the iio_dev_attr type is being extended to hold a
> >     reference for an IIO buffer;
> >     = this is great for scan_elements attributes
> >     = and for the rest of the iio_buffer attributes, it means we need to
> >       wrap them into iio_dev_attr
> >
> > Changelog v1 -> v2:
> > * https://lore.kernel.org/linux-iio/20201117162340.43924-1-alexandru.ardelean@analog.com/
> > * 'iio: buffer: rework buffer & scan_elements dir creation'
> >   add more doc-strings detailing the reasoning for this change
> > * 'iio: buffer: re-route scan_elements via it's kobj_type'
> >   move list_del() before the kfree()'s in the list destruction
> > * 'iio: buffer: introduce support for attaching more IIO buffers'
> >   - changed to 'cnt' variable vs re-using the 'i' for unwinding in
> >     iio_buffer_alloc_sysfs_and_mask()
> >   - removed kfree(old) in iio_device_attach_buffer()
> >   - made iio_device_attach_buffer() an int return; this means that some
> >     follow up patches are needed to make this return value be used;
> > * 'iio: buffer: add ioctl() to support opening extra buffers for IIO device'
> >   - tested ioctl() with a simple C program; attached to comment;
> >   - changed 'i' variable usage to 'sz' for alloc
> >   - changed logic for buffer0; returning FD 0; userspace should know
> >     that the IIO_BUFFER_GET_FD_IOCTL call returns 0 for buffer0;
> >     this is because I can't find a way to determine the FD of the
> >     ioctl() in the kernel; duplicating an ioctl() for buffer0 is also bad;
> >
> >
> > Alexandru Ardelean (24):
> >   iio: adc: ti_am335x_adc: remove omitted iio_kfifo_free()
> >   iio: kfifo: add devm_iio_kfifo_buffer_setup() helper
> >   iio: make use of devm_iio_kfifo_buffer_setup() helper
> >   iio: accel: sca3000: use devm_iio_kfifo_buffer_setup() helper
> >   iio: kfifo: un-export devm_iio_kfifo_allocate() function
> >   iio: buffer-dma,adi-axi-adc: introduce
> >     devm_iio_dmaengine_buffer_setup()
> >   docs: ioctl-number.rst: reserve IIO subsystem ioctl() space
> >   iio: core: register chardev only if needed
> >   iio: core-trigger: make iio_device_register_trigger_consumer() an int
> >     return
> >   iio: core: rework iio device group creation
> >   iio: buffer: group attr count and attr alloc
> >   iio: core: merge buffer/ & scan_elements/ attributes
> >   iio: add reference to iio buffer on iio_dev_attr
> >   iio: buffer: wrap all buffer attributes into iio_dev_attr
> >   iio: buffer: dmaengine: obtain buffer object from attribute
> >   iio: core: wrap iio device & buffer into struct for character devices
> >   iio: buffer: move __iio_buffer_free_sysfs_and_mask() before alloc
> >   iio: dummy: iio_simple_dummy_buffer: use triggered buffer core calls
> >   iio: buffer: introduce support for attaching more IIO buffers
> >   iio: buffer: add ioctl() to support opening extra buffers for IIO
> >     device
> >   iio: core: rename 'dev' -> 'indio_dev' in iio_device_alloc()
> >   tools: iio: make iioutils_get_type() private in iio_utils
> >   tools: iio: privatize globals and functions in iio_generic_buffer.c
> >     file
> >   tools: iio: convert iio_generic_buffer to use new IIO buffer API
> >
> >  .../driver-api/driver-model/devres.rst        |   3 +-
> >  .../userspace-api/ioctl/ioctl-number.rst      |   1 +
> >  drivers/iio/accel/sca3000.c                   |  19 +-
> >  drivers/iio/accel/ssp_accel_sensor.c          |  14 +-
> >  drivers/iio/adc/adi-axi-adc.c                 |  12 +-
> >  drivers/iio/adc/ina2xx-adc.c                  |  14 +-
> >  drivers/iio/adc/ti_am335x_adc.c               |  24 +-
> >  .../buffer/industrialio-buffer-dmaengine.c    |  35 +-
> >  .../buffer/industrialio-triggered-buffer.c    |  10 +-
> >  drivers/iio/buffer/kfifo_buf.c                |  40 +-
> >  .../cros_ec_sensors/cros_ec_sensors_core.c    |  13 +-
> >  drivers/iio/dummy/iio_simple_dummy_buffer.c   |  68 +--
> >  drivers/iio/gyro/ssp_gyro_sensor.c            |  14 +-
> >  drivers/iio/health/max30100.c                 |  16 +-
> >  drivers/iio/health/max30102.c                 |  16 +-
> >  drivers/iio/iio_core.h                        |  32 +-
> >  drivers/iio/iio_core_trigger.h                |   4 +-
> >  .../iio/imu/inv_icm42600/inv_icm42600_accel.c |  14 +-
> >  .../iio/imu/inv_icm42600/inv_icm42600_gyro.c  |  13 +-
> >  .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    |  15 +-
> >  drivers/iio/industrialio-buffer.c             | 494 ++++++++++++++----
> >  drivers/iio/industrialio-core.c               | 113 +++-
> >  drivers/iio/industrialio-event.c              |   6 +-
> >  drivers/iio/industrialio-trigger.c            |   6 +-
> >  drivers/iio/light/acpi-als.c                  |  12 +-
> >  drivers/iio/light/apds9960.c                  |  16 +-
> >  .../staging/iio/impedance-analyzer/ad5933.c   |  23 +-
> >  include/linux/iio/buffer-dmaengine.h          |   7 +-
> >  include/linux/iio/buffer.h                    |   4 +-
> >  include/linux/iio/buffer_impl.h               |  21 +-
> >  include/linux/iio/iio-opaque.h                |  14 +
> >  include/linux/iio/iio.h                       |   5 -
> >  include/linux/iio/kfifo_buf.h                 |   7 +-
> >  include/linux/iio/sysfs.h                     |   3 +
> >  include/uapi/linux/iio/buffer.h               |  10 +
> >  tools/iio/Makefile                            |   1 +
> >  tools/iio/iio_generic_buffer.c                | 153 ++++--
> >  tools/iio/iio_utils.c                         |  18 +-
> >  tools/iio/iio_utils.h                         |   8 +-
> >  39 files changed, 856 insertions(+), 442 deletions(-)
> >  create mode 100644 include/uapi/linux/iio/buffer.h
> >
>