On Mon, 12 Feb 2024 17:26:45 -0600
David Lechner <dlechner@xxxxxxxxxxxx> wrote:
> This modifies the ad7380 ADC driver to use spi_optimize_message() to
> optimize the SPI message for the buffered read operation. Since buffered
> reads reuse the same SPI message for each read, this can improve
> performance by reducing the overhead of setting up some parts the SPI
> message in each spi_sync() call.
>
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
> ---
> drivers/iio/adc/ad7380.c | 52 +++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 45 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
> index abd746aef868..5c5d2642a474 100644
> --- a/drivers/iio/adc/ad7380.c
> +++ b/drivers/iio/adc/ad7380.c
> @@ -133,6 +133,7 @@ struct ad7380_state {
> struct spi_device *spi;
> struct regulator *vref;
> struct regmap *regmap;
> + struct spi_message *msg;
> /*
> * DMA (thus cache coherency maintenance) requires the
> * transfer buffers to live in their own cache lines.
> @@ -231,19 +232,55 @@ static int ad7380_debugfs_reg_access(struct iio_dev *indio_dev, u32 reg,
> return ret;
> }
>
> +static int ad7380_buffer_preenable(struct iio_dev *indio_dev)
> +{
> + struct ad7380_state *st = iio_priv(indio_dev);
> + struct spi_transfer *xfer;
> + int ret;
> +
> + st->msg = spi_message_alloc(1, GFP_KERNEL);
As it only ever has one element, is there a clear advantage over
just embedding the spi_message in the structure rather than
as a separate allocation? You'd need the transfer as well.
spi_message_init_with_transfers(st->msg, &st->trans, 1);
The transfer is then also available without walking the list (though
obviously you don't walk very far ;).
> + if (!st->msg)
> + return -ENOMEM;
> +
> + xfer = list_first_entry(&st->msg->transfers, struct spi_transfer,
> + transfer_list);
> +
> + xfer->bits_per_word = st->chip_info->channels[0].scan_type.realbits;
> + xfer->len = 4;
> + xfer->rx_buf = st->scan_data.raw;
> +
> + ret = spi_optimize_message(st->spi, st->msg);
> + if (ret) {
> + spi_message_free(st->msg);
Would avoid freeing explicitly here or later if it was embedded in
struct ad7380_state
Also, this doesn't seem very dynamic in general. Anything stopping this
being done at probe() as a one time thing?
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static int ad7380_buffer_postdisable(struct iio_dev *indio_dev)
> +{
> + struct ad7380_state *st = iio_priv(indio_dev);
> +
> + spi_unoptimize_message(st->msg);
> + spi_message_free(st->msg);
> +
> + return 0;
> +}
> +
> +static const struct iio_buffer_setup_ops ad7380_buffer_setup_ops = {
> + .preenable = ad7380_buffer_preenable,
> + .postdisable = ad7380_buffer_postdisable,
> +};
> +
> static irqreturn_t ad7380_trigger_handler(int irq, void *p)
> {
> struct iio_poll_func *pf = p;
> struct iio_dev *indio_dev = pf->indio_dev;
> struct ad7380_state *st = iio_priv(indio_dev);
> - struct spi_transfer xfer = {
> - .bits_per_word = st->chip_info->channels[0].scan_type.realbits,
> - .len = 4,
> - .rx_buf = st->scan_data.raw,
> - };
> int ret;
>
> - ret = spi_sync_transfer(st->spi, &xfer, 1);
> + ret = spi_sync(st->spi, st->msg);
> if (ret)
> goto out;
>
> @@ -420,7 +457,8 @@ static int ad7380_probe(struct spi_device *spi)
>
> ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
> iio_pollfunc_store_time,
> - ad7380_trigger_handler, NULL);
> + ad7380_trigger_handler,
> + &ad7380_buffer_setup_ops);
> if (ret)
> return ret;
>
>
