Re: [PATCH 2/3] iio: test: test gain-time-scale helpers

[Matti Vaittinen]

On 1/13/24 18:12, Jonathan Cameron wrote:
> On Wed, 10 Jan 2024 12:12:55 +0200
> Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
>
> > Some light sensors can adjust both the HW-gain and integration time.
> > There are cases where adjusting the integration time has similar impact
> > to the scale of the reported values as gain setting has.
> >
> > IIO users do typically expect to handle scale by a single writable 'scale'
> > entry. Driver should then adjust the gain/time accordingly.
> >
> > It however is difficult for a driver to know whether it should change
> > gain or integration time to meet the requested scale. Usually it is
> > preferred to have longer integration time which usually improves
> > accuracy, but there may be use-cases where long measurement times can be
> > an issue. Thus it can be preferable to allow also changing the
> > integration time - but mitigate the scale impact by also changing the gain
> > underneath. Eg, if integration time change doubles the measured values,
> > the driver can reduce the HW-gain to half.
> >
> > The theory of the computations of gain-time-scale is simple. However,
> > some people (undersigned) got that implemented wrong for more than once.
> > Hence some gain-time-scale helpers were introduced.
> >
> > Add some simple tests to verify the most hairy functions.
> >
> > Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>

..

> > +static void test_iio_gts_chk_scales_all(struct kunit *test, struct iio_gts *gts,
> > +					const int *vals, int len)
> > +{
> > +	static const int gains[] = {1, 2, 4, 8, 16, 32, 64, 128, 256, 512,
> > +				    1024, 2048, 4096, 4096 * 2, 4096 * 4,
> > +				    4096 * 8};
> > +
> > +	int expected[ARRAY_SIZE(gains) * 2];
> > +	int i, ret;
> > +	int exp_len = ARRAY_SIZE(gains) * 2;
>
> Use this for expected[*] just above?

Doing:
const int exp_len = ARRAY_SIZE(gains) * 2;
int expected[exp_len];

gives me:
warning: ISO C90 forbids variable length array ‘expected’ [-Wvla]

I could drop the whole exp_len variable, but I prefer test code which is 
as obvious as it gets if any of the checks fails. For me the check:

> > +	KUNIT_EXPECT_EQ(test, exp_len, len);
> > +	if (len != exp_len)
> > +		return;

is (very slightly) more obvious than:
	KUNIT_EXPECT_EQ(test, ARRAY_SIZE(gains) * 2, len);
	if (len != ARRAY_SIZE(gains) * 2)
		return;

I guess I'll leave this one as it is. Just kick me in v2 if I 
misunderstood you :)

Yours,
	-- Matti

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

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