Re: [PATCH v2 2/2] iio: adc: ti-ads7950: allow simultaneous use of buffer and direct mode

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 21 Jul 2018 14:37:34 -0500
David Lechner <david@lechnology.com> wrote:

> This modifies the TI ADS7950 A/DC driver to allow the simultaneous use
> of both the triggered buffer and reading channels directly (via in-
> kernel API or sysfs).
> 
> The use case for this is on LEGO MINDSTORMS EV3. Two of the voltage
> channels are used in-kernel by a power supply driver, which reads the
> values using iio_read_channel_processed(). These channels are only read
> at a slow rate (<= 1Hz).  However, we want to be able to read 12 other
> channels at the same time using the triggered buffer at a high rate (>=
> 100Hz).
> 
> Signed-off-by: David Lechner <david@lechnology.com>
One slight quirk I'd missed before.  The two new buffers are used for
dma and as such need to be in a cacheline separate from anything else
that might be corrupted.  I've just move them down to below the existing
buffers which should accomplish this.

Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to play with it.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/ti-ads7950.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
> index f08c4de2bd10..eae987bef994 100644
> --- a/drivers/iio/adc/ti-ads7950.c
> +++ b/drivers/iio/adc/ti-ads7950.c
> @@ -60,6 +60,8 @@ struct ti_ads7950_state {
>  	unsigned int		vref_mv;
>  
>  	unsigned int		settings;
> +	__be16			single_tx;
> +	__be16			single_rx;
>  
>  	/*
>  	 * DMA (thus cache coherency maintenance) requires the
> @@ -287,18 +289,26 @@ static irqreturn_t ti_ads7950_trigger_handler(int irq, void *p)
>  	return IRQ_HANDLED;
>  }
>  
> -static int ti_ads7950_scan_direct(struct ti_ads7950_state *st, unsigned int ch)
> +static int ti_ads7950_scan_direct(struct iio_dev *indio_dev, unsigned int ch)
>  {
> +	struct ti_ads7950_state *st = iio_priv(indio_dev);
>  	int ret, cmd;
>  
> +	mutex_lock(&indio_dev->mlock);
> +
>  	cmd = TI_ADS7950_CR_WRITE | TI_ADS7950_CR_CHAN(ch) | st->settings;
> -	st->tx_buf[0] = cpu_to_be16(cmd);
> +	st->single_tx = cpu_to_be16(cmd);
>  
>  	ret = spi_sync(st->spi, &st->scan_single_msg);
>  	if (ret)
> -		return ret;
> +		goto out;
> +
> +	ret = be16_to_cpu(st->single_rx);
> +
> +out:
> +	mutex_unlock(&indio_dev->mlock);
>  
> -	return be16_to_cpu(st->rx_buf[0]);
> +	return ret;
>  }
>  
>  static int ti_ads7950_get_range(struct ti_ads7950_state *st)
> @@ -330,13 +340,7 @@ static int ti_ads7950_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (m) {
>  	case IIO_CHAN_INFO_RAW:
> -
> -		ret = iio_device_claim_direct_mode(indio_dev);
> -		if (ret < 0)
> -			return ret;
> -
> -		ret = ti_ads7950_scan_direct(st, chan->address);
> -		iio_device_release_direct_mode(indio_dev);
> +		ret = ti_ads7950_scan_direct(indio_dev, chan->address);
>  		if (ret < 0)
>  			return ret;
>  
> @@ -402,13 +406,13 @@ static int ti_ads7950_probe(struct spi_device *spi)
>  	 * was read at the end of the first transfer.
>  	 */
>  
> -	st->scan_single_xfer[0].tx_buf = &st->tx_buf[0];
> +	st->scan_single_xfer[0].tx_buf = &st->single_tx;
>  	st->scan_single_xfer[0].len = 2;
>  	st->scan_single_xfer[0].cs_change = 1;
> -	st->scan_single_xfer[1].tx_buf = &st->tx_buf[0];
> +	st->scan_single_xfer[1].tx_buf = &st->single_tx;
>  	st->scan_single_xfer[1].len = 2;
>  	st->scan_single_xfer[1].cs_change = 1;
> -	st->scan_single_xfer[2].rx_buf = &st->rx_buf[0];
> +	st->scan_single_xfer[2].rx_buf = &st->single_rx;
>  	st->scan_single_xfer[2].len = 2;
>  
>  	spi_message_init_with_transfers(&st->scan_single_msg,