linux-kernel - Re: [PATCH] iio: dpot-dac: mark expected switch fall-through

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Date:   Mon, 8 Oct 2018 20:42:41 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>
CC:     "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: dpot-dac: mark expected switch fall-through

On 2018-10-08 19:35, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch cases
> where we are expecting to fall through.

The way I see it, it is pretty well marked up as is. So, this paragraph
is not describing the change.

> 
> Notice that in this particular case, I replaced "...and fall through."
> with a proper "fall through", which is what GCC is expecting to find.

What is not "proper" about the existing comment? Yes yes, I *know* that
GCC is not very intelligent about it and requires hand-holding, but
blaming the existing comment for not *properly* marking an intentional
fall through is ... rich.

> 
> Addresses-Coverity-ID: 1462408 ("Missing break in switch")
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/iio/dac/dpot-dac.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/dac/dpot-dac.c b/drivers/iio/dac/dpot-dac.c
> index a791d0a..e353946 100644
> --- a/drivers/iio/dac/dpot-dac.c
> +++ b/drivers/iio/dac/dpot-dac.c
> @@ -78,7 +78,7 @@ static int dpot_dac_read_raw(struct iio_dev *indio_dev,

Adding some more context here.

		case IIO_VAL_INT:
			/*
			 * Convert integer scale to fractional scale by
			 * setting the denominator (val2) to one...
>  			 */
>  			*val2 = 1;
>  			ret = IIO_VAL_FRACTIONAL;
> -			/* ...and fall through. */
> +			/* fall through */
>  		case IIO_VAL_FRACTIONAL:
>  			*val *= regulator_get_voltage(dac->vref) / 1000;
>  			*val2 *= dac->max_ohms;
> 

Considering the above added context, I have to say that this mindless
change is not an improvement, as you have just destroyed the continued
sentence from the previous comment. You must have noticed that this
was the end of a continued sentence, as you even quoted it in the commit
message. The big question is why you did not stop to think and consider
the context?

Yes, I'm annoyed by mindless changes. Especially mindless changes aimed
at improving readability while in fact making things less readable.

TL;DR, if you are desperate to fix "the problem" with this fall through
comment, please do so in a way that preserves overall readability. And
it would be nice to not blame the existing code for brain damage in GCC
and various other static analyzers.

Cheers,
Peter