iio: buffer-dma: split iio_dma_buffer_fileio_free() function

This change splits the logic into a separate function, which will be
re-used later.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc: Alexandru Ardelean <ardeleanalex@gmail.com>
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20231219175009.65482-3-paul@crapouillou.net
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: buffer-dma: Get rid of outgoing queue

The buffer-dma code was using two queues, incoming and outgoing, to
manage the state of the blocks in use.

While this totally works, it adds some complexity to the code,
especially since the code only manages 2 blocks. It is much easier to
just check each block's state manually, and keep a counter for the next
block to dequeue.

Since the new DMABUF based API wouldn't use the outgoing queue anyway,
getting rid of it now makes the upcoming changes simpler.

With this change, the IIO_BLOCK_STATE_DEQUEUED is now useless, and can
be removed.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20231219175009.65482-2-paul@crapouillou.net
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: dma-buffer: Cleanup buffer.h/buffer_impl.h includes

The IIO DMA buffer is a DMA buffer implementation. As such it should
include buffer_impl.h rather than buffer.h.

The include to buffer.h in buffer-dma.h should be buffer_impl.h so it has
access to the struct iio_buffer definition. The code currently only works
because all places that use buffer-dma.h include buffer_impl.h before it.

The include to buffer.h in industrialio-buffer-dma.c can be removed since
those file does not reference any of buffer consumer functions.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: buffer: rename 'read_first_n' callback to 'read'

It is implied that 'read' will read the first n bytes and not e.g. bytes
only from offsets within the buffer that are a prime number.

This change is non-functional, mostly just a rename.
A secondary intent with this patch is to make room later to add a write
callback.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 177

Based on 1 normalized pattern(s):

licensed under the gpl 2

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 135 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190528170026.071193225@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

iio:buffer: make length types match kfifo types

Currently, we use int for buffer length and bytes_per_datum. However,
kfifo uses unsigned int for length and size_t for element size. We need
to make sure these matches or we will have bugs related to overflow (in
the range between INT_MAX and UINT_MAX for length, for example).

In addition, set_bytes_per_datum uses size_t while bytes_per_datum is an
int, which would cause bugs for large values of bytes_per_datum.

Change buffer length to use unsigned int and bytes_per_datum to use
size_t.

Signed-off-by: Martin Kelly <mkelly@xevo.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

vfs: do bulk POLL* -> EPOLL* replacement

This is the mindless scripted replacement of kernel use of POLL*
variables as described by Al, done by this script:

for V in IN OUT PRI ERR RDNORM RDBAND WRNORM WRBAND HUP RDHUP NVAL MSG; do
L=`git grep -l -w POLL$V | grep -v '^t' | grep -v /um/ | grep -v '^sa' | grep -v '/poll.h$'|grep -v '^D'`
for f in $L; do sed -i "-es/^\([^\"]*\)\(\<POLL$V\>\)/\\1E\\2/" $f; done
done

with de-mangling cleanups yet to come.

NOTE! On almost all architectures, the EPOLL* constants have the same
values as the POLL* constants do. But they keyword here is "almost".
For various bad reasons they aren't the same, and epoll() doesn't
actually work quite correctly in some cases due to this on Sparc et al.

The next patch from Al will sort out the final differences, and we
should be all done.

Scripted-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

iio: buffer-dma: Add missing header buffer_impl.h

Add buffer_impl.h as buffer.h was split into interface for using and
for internals. Without this industrialio-buffer-dma.c fails
to compile.

Fixes:
commit 33dd94cb972175249258329c4aaffddcc82c2005 ("iio:buffer.h - split
into buffer.h and buffer_impl.h")

Signed-off-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

iio: buffer-dma: Use ARRAY_SIZE in for loop range

Use the ARRAY_SIZE macro in the for loops that access queue->fileio.blocks.
Macro is already used in a couple of places where this access occurs,
but range was hardcoded in these locations.

Signed-off-by: Phil Reid <preid@electromag.com.au>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

iio: Add generic DMA buffer infrastructure

The traditional approach used in IIO to implement buffered capture requires
the generation of at least one interrupt per sample. In the interrupt
handler the driver reads the sample from the device and copies it to a
software buffer. This approach has a rather large per sample overhead
associated with it. And while it works fine for samplerates in the range of
up to 1000 samples per second it starts to consume a rather large share of
the available CPU processing time once we go beyond that, this is
especially true on an embedded system with limited processing power. The
regular interrupt also causes increased power consumption by not allowing
the hardware into deeper sleep states, which is something that becomes more
and more important on mobile battery powered devices.

And while the recently added watermark support mitigates some of the issues
by allowing the device to generate interrupts at a rate lower than the data
output rate, this still requires a storage buffer inside the device and
even if it exists it is only a few 100 samples deep at most.

DMA support on the other hand allows to capture multiple millions or even
more samples without any CPU interaction. This allows the CPU to either go
to sleep for longer periods or focus on other tasks which increases overall
system performance and power consumption. In addition to that some devices
might not even offer a way to read the data other than using DMA, which
makes DMA mandatory to use for them.

The tasks involved in implementing a DMA buffer can be divided into two
categories. The first category is memory buffer management (allocation,
mapping, etc.) and hooking this up the IIO buffer callbacks like read(),
enable(), disable(), etc. The second category of tasks is to setup the
DMA hardware and manage the DMA transfers. Tasks from the first category
will be very similar for all IIO drivers supporting DMA buffers, while the
tasks from the second category will be hardware specific.

This patch implements a generic infrastructure that take care of the former
tasks. It provides a set of functions that implement the standard IIO
buffer iio_buffer_access_funcs callbacks. These can either be used as is or
be overloaded and augmented with driver specific code where necessary.

For the DMA buffer support infrastructure that is introduced in this series
sample data is grouped by so called blocks. A block is the basic unit at
which data is exchanged between the application and the hardware. The
application is responsible for allocating the memory associated with the
block and then passes the block to the hardware. When the hardware has
captured the amount of samples equal to size of a block it will notify the
application, which can then read the data from the block and process it.
The block size can freely chosen (within the constraints of the hardware).
This allows to make a trade-off between latency and management overhead.
The larger the block size the lower the per sample overhead but the latency
between when the data was captured and when the application will be able to
access it increases, in a similar way smaller block sizes have a larger per
sample management overhead but a lower latency. The ideal block size thus
depends on system and application requirements.

For the time being the infrastructure only implements a simple double
buffered scheme which allocates two blocks each with half the size of the
configured buffer size. This provides basic support for capturing
continuous uninterrupted data over the existing file-IO ABI. Future
extensions to the DMA buffer infrastructure will give applications a more
fine grained control over how many blocks are allocated and the size of
each block. But this requires userspace ABI additions which are
intentionally not part of this patch and will be added separately.

Tasks of the second category need to be implemented by a device specific
driver. They can be hooked up into the generic infrastructure using two
simple callbacks, submit() and abort().

The submit() callback is used to schedule DMA transfers for blocks. Once a
DMA transfer has been completed it is expected that the buffer driver calls
iio_dma_buffer_block_done() to notify. The abort() callback is used for
stopping all pending and active DMA transfers when the buffer is disabled.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>