Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

[Sergei Shtylyov]

On 12/10/2015 08:40 PM, Geyslan G. Bem wrote:

> > > > > > > > Don't use the 'do {} while (0)' wrapper in a single statement macro.
> > > > > > > >
> > > > > > > > Caught by checkpatch: "WARNING: Single statement macros should not
> > > > > > > > use a do {} while (0) loop"
> > > > > > > >
> > > > > > > > Signed-off-by: Geyslan G. Bem <geyslan@xxxxxxxxx>
> > > > > > > > ---
> > > > > > > >      drivers/usb/host/ehci.h | 4 ++--
> > > > > > > >      1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
> > > > > > > > index cfeebd8..945000a 100644
> > > > > > > > --- a/drivers/usb/host/ehci.h
> > > > > > > > +++ b/drivers/usb/host/ehci.h
> > > > > > > > @@ -244,9 +244,9 @@ struct ehci_hcd {                   /* one per
> > > > > > > > controller */
> > > > > > > >            /* irq statistics */
> > > > > > > >      #ifdef EHCI_STATS
> > > > > > > >            struct ehci_stats       stats;
> > > > > > > > -#      define COUNT(x) do { (x)++; } while (0)
> > > > > > > > +#      define COUNT(x) ((x)++)
> > > > > > > >      #else
> > > > > > > > -#      define COUNT(x) do {} while (0)
> > > > > > > > +#      define COUNT(x) ((void) 0)
> > > > > > >
> > > > > > >       Why not just empty #define?
> > > > > >
> > > > > > Indeed. I'll change it.
> > > > > > Tks Sergei.
> > > > >
> > > > > Since COUNT is not used to return the empty #define is ok. Another way
> > > > > is to use #define COUNT(x) (0) to get a 0 when necessary to read
> > > > > returns.
> >
> > > >      Just 0, no parens please.
> >
> > > Ok, no parens, since there's no evaluation.
> >
> >     It's because the literals don't need parens at all.
> >
> > > Then my change is:
> > >
> > > -#      define COUNT(x) do { (x)++; } while (0)
> > > +#      define COUNT(x) (++(x))
> > >    #else
> > > -#      define COUNT(x) do {} while (0)
> > > +#      define COUNT(x) 0
> > >
> > > Pre-increment allowing to return the updated x.
> >
> >
> >     Why if there was a post-increment before?

> There's nothing wrong with post-increment. The pre one would be
> necessary if using return.

   Maybe it was intended to return the old value? :-)

> >     Anyway, this talk is quite pointless since the macro didn't return any
> > value anyway.
> You're sure, there's no use anywhere of the return of that macro indeed.

   *do* {} *while* (0) just couldn't return any value, it's not just a 
compound statement which gcc indeed allows to be evaluated.

> Sending v2 soon.

MBR, Sergei

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