Re: [PATCH v3 2/6] iio: light: Add gain-time-scale helpers

[Matti Vaittinen]

On 3/13/23 14:40, Andy Shevchenko wrote:
> On Sun, Mar 12, 2023 at 05:08:48PM +0000, Jonathan Cameron wrote:
> > On Sun, 12 Mar 2023 17:06:38 +0000
> > Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> > > On Mon, 6 Mar 2023 11:17:15 +0200
> > > Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
>
> ...
>
> > > Given most modern IIO drivers use fully devm_ based probing, for now I would not
> > > expose anything else.  That will reduce the interface a lot which I think
> > > is probably a good thing at this stage.

Probably at any stage :)

> > > Keep the non devm stuff internally though as it is a nice structure to have
> > > an I can see we may want some of these in non devm form in the future.

Ok. I was pondering this while writing these APIs. I was just thinking 
that _maybe_ someone has an driver where they do not use devm for a 
reason. Allowing a "non devm" variants for such is likely to be needed. 
Hence, I was thinking that having a non devm version could be beneficial 
from the start to avoid someone being tempted to just mix the readily 
available devm with manual unwinding...

> > > Similarly - for now don't expose the individual table building functions
> > > as we may never need them in drivers.  We (more or less) only support interfaces
> > > that are used and so far they aren't.

I was thinking of this too. It was just the small 'avoid extra 
operations [like unnecessary endianess conversions :p] when 
needed'-voice in me that started screaming when I though of exporting 
only the 'build all' and 'purge all' APIs...

> > > For other functions it's worth thinking about whether to not export them
> > > initially. I haven't been through them all to figure out what is not currently used.

I think I can go through them. There are a few that aren't currently used.

> > >
> > Ah. I forgot the tests that don't have a device so can't use devm.
>
> Why not? I have seen, IIRC, test cases inside the kernel that fakes the device
> for that.

I'd appreciated any pointer for such an example if you have one at hand. 
(I can do the digging if you don't though!)

I am not a fan of unit tests. They add huge amount of inertia to 
development, and in worst case, they stop people from contributing where 
improving a feature requires test code modification(s). And harder the 
test code is to understand, worse the unwanted side-effects. Also, 
harder the test code is to read, more time and effort it requires to 
analyze a test failure... Hence, I am _very_ conservative what comes to 
adding size of test code with anything that is not strictly required.

After that being said, unit tests are a great tool when carefully used - 
and I assume/hope stubbing a device for devm_ tests does not add much 
extra... But let me see if I can find an example :)

Yours,
	-- Matti

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

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