iio: mxs-lradc: compute temperature from channel 8 and 9

The mxs LRADC is able to read an internal die temperature sensor. The
temperature has to be calculated from the value read on channel 8 and channel 9.
To be able to expose the result to hwmon, implement iio channel 8 as
(channel 9 - channel 8). Then, implement IIO_CHAN_INFO_SCALE and
IIO_CHAN_INFO_OFFSET so that it can be processed by hwmon through the in kernel
provider/consumer mechanism.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/staging/iio/adc/mxs-lradc.c b/drivers/staging/iio/adc/mxs-lradc.c
index e2dd7830b3204a58541a8ec7e8fed8c68ca93bbd..5a4499c3d22abe968709d7ed49f06a50d72de045 100644 (file)
--- a/drivers/staging/iio/adc/mxs-lradc.c
+++ b/drivers/staging/iio/adc/mxs-lradc.c
@@ -759,20 +759,11 @@ static void mxs_lradc_handle_touch(struct mxs_lradc *lradc)
 /*
  * Raw I/O operations
  */
-static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
-                       const struct iio_chan_spec *chan,
-                       int *val, int *val2, long m)
+static int mxs_lradc_read_single(struct iio_dev *iio_dev, int chan, int *val)
 {
        struct mxs_lradc *lradc = iio_priv(iio_dev);
        int ret;
 
-       if (m != IIO_CHAN_INFO_RAW)
-               return -EINVAL;
-
-       /* Check for invalid channel */
-       if (chan->channel > LRADC_MAX_TOTAL_CHANS)
-               return -EINVAL;
-
        /*
         * See if there is no buffered operation in progess. If there is, simply
         * bail out. This can be improved to support both buffered and raw IO at
@@ -797,7 +788,7 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
 
        /* Clean the slot's previous content, then set new one. */
        mxs_lradc_reg_clear(lradc, LRADC_CTRL4_LRADCSELECT_MASK(0), LRADC_CTRL4);
-       mxs_lradc_reg_set(lradc, chan->channel, LRADC_CTRL4);
+       mxs_lradc_reg_set(lradc, chan, LRADC_CTRL4);
 
        mxs_lradc_reg_wrt(lradc, 0, LRADC_CH(0));
 
@@ -824,6 +815,71 @@ err:
        return ret;
 }
 
+static int mxs_lradc_read_temp(struct iio_dev *iio_dev, int *val)
+{
+       int ret, min, max;
+
+       ret = mxs_lradc_read_single(iio_dev, 8, &min);
+       if (ret != IIO_VAL_INT)
+               return ret;
+
+       ret = mxs_lradc_read_single(iio_dev, 9, &max);
+       if (ret != IIO_VAL_INT)
+               return ret;
+
+       *val = max - min;
+
+       return IIO_VAL_INT;
+}
+
+static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
+                       const struct iio_chan_spec *chan,
+                       int *val, int *val2, long m)
+{
+       /* Check for invalid channel */
+       if (chan->channel > LRADC_MAX_TOTAL_CHANS)
+               return -EINVAL;
+
+       switch (m) {
+       case IIO_CHAN_INFO_RAW:
+               if (chan->type == IIO_TEMP)
+                       return mxs_lradc_read_temp(iio_dev, val);
+
+               return mxs_lradc_read_single(iio_dev, chan->channel, val);
+
+       case IIO_CHAN_INFO_SCALE:
+               if (chan->type == IIO_TEMP) {
+                       /* From the datasheet, we have to multiply by 1.012 and
+                        * divide by 4
+                        */
+                       *val = 0;
+                       *val2 = 253000;
+                       return IIO_VAL_INT_PLUS_MICRO;
+               }
+
+               return -EINVAL;
+
+       case IIO_CHAN_INFO_OFFSET:
+               if (chan->type == IIO_TEMP) {
+                       /* The calculated value from the ADC is in Kelvin, we
+                        * want Celsius for hwmon so the offset is
+                        * -272.15 * scale
+                        */
+                       *val = -1075;
+                       *val2 = 691699;
+
+                       return IIO_VAL_INT_PLUS_MICRO;
+               }
+
+               return -EINVAL;
+
+       default:
+               break;
+       }
+
+       return -EINVAL;
+}
+
 static const struct iio_info mxs_lradc_iio_info = {
        .driver_module          = THIS_MODULE,
        .read_raw               = mxs_lradc_read_raw,
@@ -1151,8 +1207,17 @@ static const struct iio_chan_spec mxs_lradc_chan_spec[] = {
        MXS_ADC_CHAN(5, IIO_VOLTAGE),
        MXS_ADC_CHAN(6, IIO_VOLTAGE),
        MXS_ADC_CHAN(7, IIO_VOLTAGE),   /* VBATT */
-       MXS_ADC_CHAN(8, IIO_TEMP),      /* Temp sense 0 */
-       MXS_ADC_CHAN(9, IIO_TEMP),      /* Temp sense 1 */
+       /* Combined Temperature sensors */
+       {
+               .type = IIO_TEMP,
+               .indexed = 1,
+               .scan_index = 8,
+               .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+                                     BIT(IIO_CHAN_INFO_OFFSET) |
+                                     BIT(IIO_CHAN_INFO_SCALE),
+               .channel = 8,
+               .scan_type = {.sign = 'u', .realbits = 18, .storagebits = 32,},
+       },
        MXS_ADC_CHAN(10, IIO_VOLTAGE),  /* VDDIO */
        MXS_ADC_CHAN(11, IIO_VOLTAGE),  /* VTH */
        MXS_ADC_CHAN(12, IIO_VOLTAGE),  /* VDDA */