linux-kernel - Re: [PATCH v2 5/5] iio: afe: iio-rescale: Re-use generic struct s32

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Message-ID: <YfK1XSfVW8P+gzd/@smile.fi.intel.com>
Date:   Thu, 27 Jan 2022 17:08:13 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Liam Beguin <liambeguin@...il.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Andreas Kemnade <andreas@...nade.info>,
        linux-arm-msm@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH v2 5/5] iio: afe: iio-rescale: Re-use generic struct
 s32_fract

On Thu, Jan 27, 2022 at 12:03:49PM +0100, Peter Rosin wrote:
> On 2022-01-26 14:01, Andy Shevchenko wrote:
> > On Wed, Jan 26, 2022 at 01:35:09PM +0100, Peter Rosin wrote:
> >> On 2022-01-26 13:04, Andy Shevchenko wrote:
> >>> On Wed, Jan 26, 2022 at 11:26:50AM +0100, Peter Rosin wrote:
> >>>> It's easy to both remove and to add back "the bigger object". I just
> >>>> don't see the point of the churn. Technically you can probably rearrange
> >>>> stuff in probe and remove the 2nd argument to ->props() altogether and
> >>>> chase pointers from the dev object instead. I don't see the point of
> >>>> that either. It doesn't really make things simpler, it doesn't really
> >>>> make things easier to read. To me, it's just pointless churn.
> >>>
> >>> Since you still haven't got a point the conclusions are wrong.
> >>> The point is (I dunno how more clear to make it) is to have proper
> >>> layering from the (current) design perspective.
> >>
> >> I think got the gist of it. I simply do not agree with your conclusion
> >> about what the "proper layering" should be.
> > 
> > And I see no real argument against it. With the patch applied I see
> > a better structure of the code and exactly necessary data to be passed
> > to the method. Which makes me think that current implementation is
> > either a leftover or was something like "let's take a bigger object
> > _just in case_", which I can't take as a proper layering.
> 
> The bigger object, or the one and only object as the current code is
> written, is given to ->props() by design.
> 
> BTW, you don't seem to understand the ->props() functions. There is no
> data "passed to" the ->props() functions. These functions instead fill
> in properties. Currently this boils down to the scaling fraction, but I
> can imagine other properties.

Currently the object of the properties is the same as struct __Txx_fract.
In the future it may indeed be expanded. In such case I see that the layering
might look like

struct ..._props {
	struct __Txx_fract fract;
	...
};

Of course it depends on the properties themselves, but at least that's
how I believe the OOP paradigm works. Am I mistaken?

> On 2022-01-25 19:17, Andy Shevchenko wrote:
> >                              The bigger object would be needed
> > in case of using data that is not fraction. Either way it would
> > be easy to add a container_of() than supply unneeded data to
> > the method.
> 
> You argued that it is easy to "break out" to the bigger object in case
> it's needed. Which in my book is a sign of poor layering.
> It's way easier to *not* change things, it's perfectly fine as-is.
> 
> The argument against making the change you propose is that it does not
> make this small driver any easier to understand. It would still just
> change things for the sake of changing them, and I do not see the point
> of erasing the existing future-proofing when it has no cost.
> 
> To sum up, I'm ok with introducing fract_s32 in this driver, but I
> don't agree with the signature change of ->props().

Thanks for valuable comments!

I postponed the change in any case, let Liam to finish his part first,
which we agreed is more important.


-- 
With Best Regards,
Andy Shevchenko