Hi Nuno,
On 6/19/24 07:47, Nuno Sá wrote:
On Tue, 2024-06-18 at 18:08 +0200, Olivier Moysan wrote:
Add scaling support to STM32 DFSDM.
Signed-off-by: Olivier Moysan <olivier.moysan@xxxxxxxxxxx>
---
Just some general comments...
Acked-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
drivers/iio/adc/Kconfig | 1 +
drivers/iio/adc/stm32-dfsdm-adc.c | 94 ++++++++++++++++++++++++++++++-
2 files changed, 92 insertions(+), 3 deletions(-)
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index f3dfdaa80678..858ae8161fa4 100644
...
@@ -1301,6 +1339,8 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,
ret = stm32_dfsdm_single_conv(indio_dev, chan, val);
if (adc->hwc)
iio_hw_consumer_disable(adc->hwc);
+ if (adc->backend[idx])
+ iio_backend_disable(&indio_dev->dev, adc->backend[idx]);
if (ret < 0) {
dev_err(&indio_dev->dev,
"%s: Conversion failed (channel %d)\n",
@@ -1320,6 +1360,45 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,
*val = adc->sample_freq;
return IIO_VAL_INT;
+
+ case IIO_CHAN_INFO_SCALE:
+ /*
+ * Scale is expressed in mV.
+ * When fast mode is disabled, actual resolution may be lower
+ * than 2^n, where n=realbits-1.
+ * This leads to underestimating input voltage. To
+ * compensate this deviation, the voltage reference can be
+ * corrected with a factor = realbits resolution / actual max
+ */
+ if (adc->backend[idx]) {
+ iio_backend_read_raw(adc->backend[idx], val, val2, mask);
+
This is something that I've been thinking about since the beginning of backends
support. Basically having the "catch all" read_raw()/write_raw() or more dedicated
interfaces. For example, in your usecase I think it would make more sense to have
dedicated API's like iio_backend_read_scale() and iio_backend_read_offset() as you're
extending that functionality. Calling iio_backend_read_raw() seems a bit weird to me.
OTOH, iio_backend_read_raw() could be useful in cases where frontends call
iio_backend_extend_chan_spec() and may get some functionality they are not aware of.
And so, in the default: statement this "catch all" API could be used.
Anyways, this are really minor (likely pedantic) details and you kind of came first
and made the decision for me. As I don't really have strong feelings about it, I'm
fine with it as-is.
My first idea was to stick to IIO read_raw API ('struct iio_chan_spec
const *chan' should at least be added to prototype as you pointed it
out). But I agree that iio_backend_read_raw() is not explicit regarding
the requested info.
I consider using the existing API iio_backend_ext_info_get() for v2, as
you suggested.
BRs
Olivier
+ *val = div_u64((u64)*val * (u64)BIT(DFSDM_DATA_RES - 1),
max);
+ *val2 = chan->scan_type.realbits;
+ if (chan->differential)
+ *val *= 2;
+ }
+ return IIO_VAL_FRACTIONAL_LOG2;
+
+ case IIO_CHAN_INFO_OFFSET:
+ /*
+ * DFSDM output data are in the range [-2^n,2^n],
+ * with n=realbits-1.
+ * - Differential modulator:
+ * Offset correspond to SD modulator offset.
+ * - Single ended modulator:
+ * Input is in [0V,Vref] range, where 0V corresponds to -2^n, and
Vref to 2^n.
+ * Add 2^n to offset. (i.e. middle of input range)
+ * offset = offset(sd) * vref / res(sd) * max / vref.
+ */
+ if (adc->backend[idx]) {
+ iio_backend_read_raw(adc->backend[idx], val, val2, mask);
+
+ *val = div_u64((u64)max * *val, BIT(*val2 - 1));
+ if (!chan->differential)
+ *val += max;
+ }
+ return IIO_VAL_INT;
}
return -EINVAL;
@@ -1449,7 +1528,15 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev
*indio_dev, struct iio_c
* IIO_CHAN_INFO_RAW: used to compute regular conversion
* IIO_CHAN_INFO_OVERSAMPLING_RATIO: used to set oversampling
*/
- ch->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+ if (child) {
+ ch->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+ BIT(IIO_CHAN_INFO_SCALE) |
+ BIT(IIO_CHAN_INFO_OFFSET);
Not sure if the above SCALE and OFFSET are solely properties if the backend. If so,
you could maybe use iio_backend_extend_chan_spec().
- Nuno Sá
