linux-kernel - Re: [PATCH v4 4/6] iio: light: stk3310: use dev_err

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Message-ID: <20241123144010.38871d3c@jic23-huawei>
Date: Sat, 23 Nov 2024 14:40:10 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Aren <aren@...cevolution.org>
Cc: Uwe Kleine-König <u.kleine-koenig@...libre.com>,
 Andy Shevchenko <andy.shevchenko@...il.com>, Lars-Peter Clausen
 <lars@...afoo.de>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Chen-Yu Tsai
 <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland
 <samuel@...lland.org>, Kaustabh Chakraborty <kauschluss@...root.org>,
 Barnabás Czémán <trabarni@...il.com>, Ondrej Jirman
 <megi@....cz>, linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-sunxi@...ts.linux.dev, Dragan Simic <dsimic@...jaro.org>,
 phone-devel@...r.kernel.org
Subject: Re: [PATCH v4 4/6] iio: light: stk3310: use dev_err_probe where
 possible

On Tue, 12 Nov 2024 18:11:37 -0500
Aren <aren@...cevolution.org> wrote:

> On Tue, Nov 12, 2024 at 11:15:54AM +0100, Uwe Kleine-König wrote:
> > Hello Andy, hello Aren,
> > 
> > On Mon, Nov 11, 2024 at 11:44:51AM +0200, Andy Shevchenko wrote:  
> > > On Sun, Nov 10, 2024 at 04:34:30PM -0500, Aren wrote:  
> > > > On Sun, Nov 10, 2024 at 09:52:32PM +0200, Andy Shevchenko wrote:  
> > > > > Sun, Nov 10, 2024 at 02:14:24PM -0500, Aren kirjoitti:  
> > > 
> > > You can do it differently
> > > 
> > > #define STK3310_REGFIELD(name)							\
> > > do {										\
> > > 	data->reg_##name =							\
> > > 		devm_regmap_field_alloc(dev, regmap, stk3310_reg_field_##name);	\
> > > 	if (IS_ERR(data->reg_##name))						\
> > > 		return dev_err_probe(dev, PTR_ERR(data->reg_##name),		\
> > > 				     "reg field alloc failed.\n");		\
> > > } while (0)
> > >   
> > > > #define STK3310_REGFIELD(name) ({						\
> > > > 	data->reg_##name = devm_regmap_field_alloc(dev, regmap,			\
> > > > 						   stk3310_reg_field_##name);   \
> > > > 	if (IS_ERR(data->reg_##name))						\
> > > > 		return dev_err_probe(dev, PTR_ERR(data->reg_##name),		\
> > > > 				     "reg field alloc failed\n");		\
> > > > })  
> > > 
> > > I am against unneeded use of GNU extensions.
> > >   
> > > > > > replacing "do { } while (0)" with "({ })" and deindenting could make
> > > > > > enough room to clean this up the formatting of this macro though.  
> > > > > 
> > > > > do {} while (0) is C standard, ({}) is not.  
> > > > 
> > > > ({ }) is used throughout the kernel, and is documented as such[1]. I
> > > > don't see a reason to avoid it, if it helps readability.  
> > > 
> > > I don't see how it makes things better here, and not everybody is familiar with
> > > the concept even if it's used in the kernel here and there. Also if a tool is
> > > being used in one case it doesn't mean it's suitable for another.  
> > 
> > Just to throw in my subjective view here: I don't expect anyone with
> > some base level knowledge of C will have doubts about the semantics of
> > ({ ... }) and compared to that I find do { ... } while (0) less optimal,
> > because it's more verbose and when spotting the "do {" part, the
> > semantic only gets clear when you also see the "while (0)". Having said
> > that I also dislike the "do" starting on column 0, IMHO the RHS of the
> > #define should be intended.  
> 
> Thank you, this sums up my opinion on this better than I could have (and
> some bits I hadn't considered).
> 
> > So if you ask me, this is not an unneeded use of an extension. The
> > extension is used to improve readabilty and I blame the C standard to
> > not support this syntax.
> > 
> > While I'm in critics mode: I consider hiding a return in a macro bad
> > style.  
> 
> Yeah... probably worse than any of the formatting options here. I guess
> the proper way would be to use devm_regmap_field_bulk_alloc, but that's
> well outside the scope of this series. Perhaps it would make sense to
> move the macro definition to just before the function it's used in so
> it's at least a little easier to spot?

It's only used 8 times.  I'd just get rid of the macro - which now
has even less advantage as the change here reduces the length of the
macro.

Normally I'd argue it should be a precursor patch, but here I think it is
fine to just do it in this patch to avoid a lot of churn.

No macro, no disagreement on formatting ;)

I'm not really sure why I let this macro in to begin with. I normally
push back on this sort of thing. Must have been a low caffeine day :(

Jonathan


> 
>  - Aren