On 12/19/20 2:41 PM, Linus Walleij wrote:
> Before trying the custom method of reading the sensor
> as raw and then converting assuming 1000 scaling, just
> use iio_read_channel_processed() which first tries to
> see if the ADC can provide a processed value directly,
> else reads raw and applies scaling inside of IIO
> using the scale attributes of the ADC.
>
> The code that hardcodes scaling to 1000 and assumes
> a 12bit ADC is very dubious. I keep it around here
> but I have a strong urge to just delete it.
>
> This gives correct readings on the AB8500 thermistor
> inputs used in the Ux500 HREFP520 platform for reading
> battery and board temperature.
>
> Cc: Peter Rosin <peda@xxxxxxxxxx>
> Cc: Chris Lesiak <chris.lesiak@xxxxxxxxx>
> Cc: Jonathan Cameron <jic23@xxxxxxxxx>
> Cc: linux-iio@xxxxxxxxxxxxxxx
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> drivers/hwmon/ntc_thermistor.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
> index 3aad62a0e661..ac0d80faddf6 100644
> --- a/drivers/hwmon/ntc_thermistor.c
> +++ b/drivers/hwmon/ntc_thermistor.c
> @@ -326,18 +326,29 @@ struct ntc_data {
> static int ntc_adc_iio_read(struct ntc_thermistor_platform_data *pdata)
> {
> struct iio_channel *channel = pdata->chan;
> - int raw, uv, ret;
> + int uv, ret;
>
> - ret = iio_read_channel_raw(channel, &raw);
> + /* A processed voltage channel will return microvolts */
> + ret = iio_read_channel_processed(channel, &uv);
> if (ret < 0) {
> - pr_err("read channel() error: %d\n", ret);
> - return ret;
> - }
> + int raw;
>
> - ret = iio_convert_raw_to_processed(channel, raw, &uv, 1000);
> - if (ret < 0) {
> - /* Assume 12 bit ADC with vref at pullup_uv */
> - uv = (pdata->pullup_uv * (s64)raw) >> 12;
> + /*
> + * FIXME: This fallback to using a raw read and then right
> + * out assume the ADC is 12 bits and hard-coding scale
> + * to 1000 seems a bit dangerous. Should it simply be
> + * deleted?
> + */
The hwmon ABI specifically supports unscaled values, which can then be
scaled in userspace using the sensors configuration file.
Given that we return the pseudo-scaled value to userspace today,
it seems to me that it would do more harm to change that instead of just
leaving it in place.
Either case, calling iio_convert_raw_to_processed() does not seem to add
value here. This is already done by iio_read_channel_processed().
The best we can do is to use the original fallback.
Guenter
> + ret = iio_read_channel_raw(channel, &raw);
> + if (ret < 0) {
> + pr_err("read channel() error: %d\n", ret);
> + return ret;
> + }
> + ret = iio_convert_raw_to_processed(channel, raw, &uv, 1000);
> + if (ret < 0) {
> + /* Assume 12 bit ADC with vref at pullup_uv */
> + uv = (pdata->pullup_uv * (s64)raw) >> 12;
> + }
> }
>
> return uv;
>
