Re: [PATCH v2 2/3] iio: pressure: Support ROHM BU1390

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On 9/19/23 17:32, Jonathan Cameron wrote:

+static int bm1390_read_raw(struct iio_dev *idev,
+               struct iio_chan_spec const *chan,
+               int *val, int *val2, long mask)
+{
+    struct bm1390_data *data = iio_priv(idev);
+    int ret;
+
+    switch (mask) {
+    case IIO_CHAN_INFO_SCALE:
+        if (chan->type == IIO_TEMP) {
+            *val = 31;
+            *val2 = 250000;
+
+            return IIO_VAL_INT_PLUS_MICRO;
+        } else if (chan->type == IIO_PRESSURE) {
+            *val = 0;
+            /*
+             * pressure in hPa is register value divided by 2048.
+             * This means kPa is 1/20480 times the register value,
+             * which equals to 48828.125 * 10 ^ -9
+             * This is 48828.125 nano kPa.
+             *
+             * When we scale this using IIO_VAL_INT_PLUS_NANO we
+             * get 48828 - which means we lose some accuracy. Well,
+             * let's try to live with that.
+             */
+            *val2 = 48828;
+
+            return IIO_VAL_INT_PLUS_NANO;
+        }
+
+        return -EINVAL;
+    case IIO_CHAN_INFO_RAW:
+        ret = iio_device_claim_direct_mode(idev);
+        if (ret)
+            return ret;
+
+        ret = bm1390_read_data(data, chan, val, val2);
+        iio_device_release_direct_mode(idev);
+        if (ret)
+            return ret;
+
+        return IIO_VAL_INT;
+    default:
+        return -EINVAL;

Certainly useless, but should we break and return -EINVAL after the
switch, so that it is more explicit that bm1390_read_raw() always
returns a value?

I think there is also opposite opinions on this. For my eyes the return
at the end of the function would also be clearer - but I think I have
been asked to drop the useless return when I've been working with other
sensors in IIO domain :) My personal preference would definitely be:

int ret;

switch (foo)
{
case BAR:
	ret = func1();
	if (ret)
		break;

	ret = func2();
	if (ret)
		break;

...
	break;

case BAZ:
	ret = -EINVAL;
	break;
}

return ret;

- but I've learned to think this is not the IIO preference.

Some static analyzers get confused (probably when there is a little
bit more going on after the function) by that and moan that some
cases are not considered in the switch.  I got annoyed enough with the
noise they were generating to advocate always having explicit defaults.

Oh, yes. I see I omitted the default from the example - but this was not what I tried to highlight ;) With a bit more thought I would've added:

default:
	ret = -EINVAL;
	break;

As you probably guess, what I was after is that for a simple (not deeply nested) cases like this, I would rather use a variable for return value and a single point of exit at the end of the function - instead of having returns in the switch-case. That'd suit better _my_ taste.

Yours,
	-- Matti

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~




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