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

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Message-ID: <20181014180134.287c0a66@archlinux>
Date:   Sun, 14 Oct 2018 18:01:34 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Rosin <peda@...ntia.se>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        "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 Sat, 13 Oct 2018 15:14:34 +0000
Peter Rosin <peda@...ntia.se> wrote:

> On 2018-10-13 14:38, Jonathan Cameron wrote:
> > On Mon, 8 Oct 2018 20:42:41 +0000
> > Peter Rosin <peda@...ntia.se> wrote:
> >   
> >> 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  
> > I agree with you in principle Peter and have tweaked the patch description
> > to make it clearer that we are doing this to make GCC static analysis more
> > helpful (suppressing a false warning is a worthwhile if you are dealing with
> > lots of them).
> > 
> > However, nice though it is to have elegant comment structure I think we
> > should still have this patch in place.  This effort to 'fix' these
> > warnings has already identified a few places where it was wrong so
> > I'm keen to see it applied by default even if it isn't perfect.  
> 
> I still object. It would have been so damn easy and it does not take a whole
> lot of imagination to quiet down GCC while keeping the comments readable. Just
> move the "and" to the previous comment, like this.
> 
> 		case IIO_VAL_INT:
> 			/*
> 			 * Convert integer scale to fractional scale by
> 			 * setting the denominator (val2) to one, and...
> 			 */
> 			*val2 = 1;
> 			ret = IIO_VAL_FRACTIONAL;
> 			/* fall through */
> 		case IIO_VAL_FRACTIONAL:
> 
> Or add a sentence, like this (which is a bit more fun IMO)
> 
> 		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. Say it again for GCC. */
> 			/* fall through */
> 		case IIO_VAL_FRACTIONAL:
> 
> Cheers,
> Peter

Done the first of the above...

Thanks,

Jonathan