linux-kernel - Re: [PATCH v2] iio: adc: New driver for TI ADS7950 chips

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Date:   Mon, 21 Nov 2016 13:52:34 -0600
From:   David Lechner <david@...hnology.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: New driver for TI ADS7950 chips

On 11/20/2016 12:28 PM, David Lechner wrote:
> This adds a new driver for the TI ADS7950 family of ADC chips. These
> communicate using SPI and come in 8/10/12-bit and 4/8/12/16 channel
> varieties.
>
> Signed-off-by: David Lechner <david@...hnology.com>
> ---
>
> v2 changes:
>
> * Got rid of XX wildcards - using ADS7950 everywhere
> * Fixed some macro parentheses issues
> * Added TI_ prefix to macros to match ti_ prefixes used elsewhere
> * Added space in rx_buf for holding timestamp
> * Use iio_device_claim_direct_mode() and spi_message_init_with_transfers()
>   helper functions
> * Don't use dev_info() at end of probe
> * Minor spelling and code style fixes
>
>  drivers/iio/adc/Kconfig      |  13 ++
>  drivers/iio/adc/Makefile     |   1 +
>  drivers/iio/adc/ti-ads7950.c | 488 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 502 insertions(+)
>  create mode 100644 drivers/iio/adc/ti-ads7950.c
>

...

> diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
> new file mode 100644
> index 0000000..d0b76bd
> --- /dev/null
> +++ b/drivers/iio/adc/ti-ads7950.c

...

> +static irqreturn_t ti_ads7950_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct ti_ads7950_state *st = iio_priv(indio_dev);
> +	int b_sent;
> +
> +	b_sent = spi_sync(st->spi, &st->ring_msg);

hmm, I copied this from another driver, but spi_sync() in IRQ handler 
does not sound like a good idea (spi_sync() can sleep). I will replace 
it with spi_async().


> +	if (b_sent)
> +		goto done;
> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, st->rx_buf,
> +					   iio_get_time_ns(indio_dev));
> +
> +done:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}

...

> +static int ti_ads7950_read_raw(struct iio_dev *indio_dev,
> +			       struct iio_chan_spec const *chan,
> +			       int *val, int *val2, long m)
> +{
> +	struct ti_ads7950_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	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);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (chan->address != TI_ADS7950_EXTRACT(ret, 12, 4))
> +			return -EIO;
> +
> +		*val = TI_ADS7950_EXTRACT(ret, 0, 12);

I'm not sure if I am doing this right. There are 8- 10- and 12-bit 
versions of this chip. The 8- and 10-bit versions still return a 12-bit 
number where the last 4 or 2 bits are always 0. Should I be shifting the 
12-bit value here based on the chip being used so that *val is 0-255 for 
8-bit and 0-1023 for 10-bit? Or should this be *really* raw and not even 
use TI_ADS7950_EXTRACT() to mask the channel address bits?

> +
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		ret = ti_ads7950_get_range(st);
> +		if (ret < 0)
> +			return ret;
> +
> +		*val = ret;
> +		*val2 = chan->scan_type.realbits;
> +
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	}
> +
> +	return -EINVAL;
> +}