iio: allow userspace to flush the hwfifo with non-blocking reads

This patch changes the semantics of non-blocking reads so that a
hardware fifo flush is triggered if the available data in the device
buffer is less then the requested size.

This allows userspace to accurately generate hardware fifo flushes, by
doing a non-blocking read with a size greater then the sum of the
device buffer and hardware fifo size.

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 6eee1b0..f72be48 100644 (file)
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -71,8 +71,9 @@ static bool iio_buffer_ready(struct iio_dev *indio_dev, struct iio_buffer *buf,
 
        if (avail >= to_wait) {
                /* force a flush for non-blocking reads */
-               if (!to_wait && !avail && to_flush)
-                       iio_buffer_flush_hwfifo(indio_dev, buf, to_flush);
+               if (!to_wait && avail < to_flush)
+                       iio_buffer_flush_hwfifo(indio_dev, buf,
+                                               to_flush - avail);
                return true;
        }
 
@@ -100,8 +101,7 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
        struct iio_dev *indio_dev = filp->private_data;
        struct iio_buffer *rb = indio_dev->buffer;
        size_t datum_size;
-       size_t to_wait = 0;
-       size_t to_read;
+       size_t to_wait;
        int ret;
 
        if (!indio_dev->info)
@@ -119,14 +119,14 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
        if (!datum_size)
                return 0;
 
-       to_read = min_t(size_t, n / datum_size, rb->watermark);
-
-       if (!(filp->f_flags & O_NONBLOCK))
-               to_wait = to_read;
+       if (filp->f_flags & O_NONBLOCK)
+               to_wait = 0;
+       else
+               to_wait = min_t(size_t, n / datum_size, rb->watermark);
 
        do {
                ret = wait_event_interruptible(rb->pollq,
-                       iio_buffer_ready(indio_dev, rb, to_wait, to_read));
+                     iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size));
                if (ret)
                        return ret;