On 20/07/16 13:37, Quentin Schulz wrote:

On 18/07/2016 15:18, Jonathan Cameron wrote:
[...]

quoted

quoted

+
+	if (!wait_for_completion_timeout(&info->completion,
+					 msecs_to_jiffies(100))) {
+		ret = -ETIMEDOUT;
+		goto out;
+	}
+
+	if (info->flags & SUNXI_GPADC_ARCH_SUN4I)
+		*val = info->temp_data * 133 - 257000;

Why report as processed?  I'd just report them as raw with the scale
and offset provided.  It's not a big thing, but if we can leave it so
that the conversion only occurs when desired, why not?

For in kernel users, this all happen 'automagically' anyway ;)

Mmmmh, in the code above we apply the scale on the raw value and then
the offset. While in iio_convert_raw_to_processed
(http://lxr.free-electrons.com/source/drivers/iio/inkern.c#L507), the
offset is applied before the scale.

The way would be to factorize the computation by scale:
Now: *val = raw * scale + offset
Then: *val = (raw + offset/scale) * scale

But the offset is an integer and offset/scale is therefore rounded.
Currently, we have the following values:
sun4i: -257000/133 = -1932.3308270676691
sun5i: -144700/100 = -1447
sun6i: -271000/167 = -1622.754491017964

Do we accept such rounding?

Yes - how accurate do you think a temp sensor is - really not a problem.

If not, we either stay with the processed value in read_raw or patch
inkern to add an offset to apply after having applied the scale to the
raw value (val2 from iio_channel_read is yet unused with
IIO_CHAN_INFO_OFFSET for example, we could use that to specify an
offset2 to apply after the switch(scale_type)-case).

I don't really care that much if you just want to keep them as
processed values.

J

[...]
Quentin