On Mon, 25 Mar 2024 17:03:13 -0500
David Lechner <dlechner@xxxxxxxxxxxx> wrote:
> This modifies the ad7944 driver to use spi_optimize_message() to reduce
> CPU usage and increase the max sample rate by avoiding repeating
> validation of the spi message on each transfer.
>
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
One buglet inline. Otherwise looks fine to me.
Jonathan
> ---
> drivers/iio/adc/ad7944.c | 177 +++++++++++++++++++++++++++--------------------
> 1 file changed, 103 insertions(+), 74 deletions(-)
>
> diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c
> index 261a3f645fd8..c767401712af 100644
> --- a/drivers/iio/adc/ad7944.c
> +++ b/drivers/iio/adc/ad7944.c
> @@ -51,6 +51,8 @@ static const char * const ad7944_spi_modes[] = {
> struct ad7944_adc {
> struct spi_device *spi;
> enum ad7944_spi_mode spi_mode;
> + struct spi_transfer xfers[3];
> + struct spi_message msg;
> /* Chip-specific timing specifications. */
> const struct ad7944_timing_spec *timing_spec;
> /* GPIO connected to CNV pin. */
> @@ -130,6 +132,88 @@ AD7944_DEFINE_CHIP_INFO(ad7985, ad7944, 16, 0);
> /* fully differential */
> AD7944_DEFINE_CHIP_INFO(ad7986, ad7986, 18, 1);
>
> +static void ad7944_unoptimize_msg(void *msg)
> +{
> + spi_unoptimize_message(msg);
> +}
> +
> +static int ad7944_3wire_cs_mode_init_msg(struct device *dev, struct ad7944_adc *adc,
> + const struct iio_chan_spec *chan)
> +{
> + unsigned int t_conv_ns = adc->always_turbo ? adc->timing_spec->turbo_conv_ns
> + : adc->timing_spec->conv_ns;
> + struct spi_transfer *xfers = adc->xfers;
> + int ret;
> +
> + /*
> + * NB: can get better performance from some SPI controllers if we use
> + * the same bits_per_word in every transfer.
> + */
> + xfers[0].bits_per_word = chan->scan_type.realbits;
> + /*
> + * CS is tied to CNV and we need a low to high transition to start the
> + * conversion, so place CNV low for t_QUIET to prepare for this.
> + */
> + xfers[0].delay.value = T_QUIET_NS;
> + xfers[0].delay.unit = SPI_DELAY_UNIT_NSECS;
> +
> + /*
> + * CS has to be high for full conversion time to avoid triggering the
> + * busy indication.
> + */
> + xfers[1].cs_off = 1;
> + xfers[1].delay.value = t_conv_ns;
> + xfers[1].delay.unit = SPI_DELAY_UNIT_NSECS;
> + xfers[0].bits_per_word = chan->scan_type.realbits;
0 ?
> +
> + /* Then we can read the data during the acquisition phase */
> + xfers[2].rx_buf = &adc->sample.raw;
> + xfers[2].len = BITS_TO_BYTES(chan->scan_type.storagebits);
> + xfers[2].bits_per_word = chan->scan_type.realbits;
> +
> + spi_message_init_with_transfers(&adc->msg, xfers, 3);
> +
> + ret = spi_optimize_message(adc->spi, &adc->msg);
> + if (ret)
> + return ret;
> +
> + return devm_add_action_or_reset(dev, ad7944_unoptimize_msg, &adc->msg);
> +}
