staging:iio:ad7476: Avoid alloc/free for each sample in buffered mode

The ad7476 driver has only support for 1 channel ADCs. So the upper limit for
the buffer size is the size of one sample plus the size of the timestamp.
Preallocate a buffer large enough to hold this to avoid having to allocate and
free a new buffer for each sample being captured.

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

diff --git a/drivers/staging/iio/adc/ad7476.h b/drivers/staging/iio/adc/ad7476.h
index 6085fad2116528e693a5c0a813fd09781eec17d7..c4f11509920a3afa2e06fc56efee2fb19cb0fc36 100644 (file)
--- a/drivers/staging/iio/adc/ad7476.h
+++ b/drivers/staging/iio/adc/ad7476.h
@@ -33,8 +33,11 @@ struct ad7476_state {
        /*
         * DMA (thus cache coherency maintenance) requires the
         * transfer buffers to live in their own cache lines.
+        * Make the buffer large enough for one 16 bit sample and one 64 bit
+        * aligned 64 bit timestamp.
         */
-       unsigned char                   data[2] ____cacheline_aligned;
+       unsigned char data[ALIGN(2, sizeof(s64)) + sizeof(s64)]
+                       ____cacheline_aligned;
 };
 
 enum ad7476_supported_device_ids {

diff --git a/drivers/staging/iio/adc/ad7476_ring.c b/drivers/staging/iio/adc/ad7476_ring.c
index 940681f29b87b8c20e5379b7ad25f6820f58314b..3c869b05f2092b16b9748b87314505379ca08230 100644 (file)
--- a/drivers/staging/iio/adc/ad7476_ring.c
+++ b/drivers/staging/iio/adc/ad7476_ring.c
@@ -26,28 +26,20 @@ static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
        struct iio_dev *indio_dev = pf->indio_dev;
        struct ad7476_state *st = iio_priv(indio_dev);
        s64 time_ns;
-       __u8 *rxbuf;
        int b_sent;
 
-       rxbuf = kzalloc(indio_dev->scan_bytes, GFP_KERNEL);
-       if (rxbuf == NULL)
-               goto done;
-
-       b_sent = spi_read(st->spi, rxbuf,
-                         st->chip_info->channel[0].scan_type.storagebits / 8);
+       b_sent = spi_sync(st->spi, &st->msg);
        if (b_sent < 0)
                goto done;
 
        time_ns = iio_get_time_ns();
 
        if (indio_dev->scan_timestamp)
-               memcpy(rxbuf + indio_dev->scan_bytes - sizeof(s64),
-                       &time_ns, sizeof(time_ns));
+               ((s64 *)st->data)[1] = time_ns;
 
-       iio_push_to_buffer(indio_dev->buffer, rxbuf);
+       iio_push_to_buffer(indio_dev->buffer, st->data);
 done:
        iio_trigger_notify_done(indio_dev->trig);
-       kfree(rxbuf);
 
        return IRQ_HANDLED;
 }