linux-kernel - Re: [PATCH] iio: adc: ad7944: use spi_optimize

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Message-ID: <20240326172149.00004247@Huawei.com>
Date: Tue, 26 Mar 2024 17:21:49 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: David Lechner <dlechner@...libre.com>
CC: Jonathan Cameron <jic23@...nel.org>, Michael Hennerich
	<Michael.Hennerich@...log.com>, Nuno Sá
	<nuno.sa@...log.com>, <linux-iio@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: adc: ad7944: use spi_optimize_message()

On Mon, 25 Mar 2024 17:03:13 -0500
David Lechner <dlechner@...libre.com> 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@...libre.com>
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);
> +}