Re: [PATCH] m68k: atari: Make Atari ROM port I/O write macros return void

[Guenter Roeck]

On 5/20/22 08:07, Geert Uytterhoeven wrote:
> Hi Günter,
>
> On Fri, May 20, 2022 at 4:52 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 5/20/22 07:32, Geert Uytterhoeven wrote:
> > > The macros implementing Atari ROM port I/O writes do not cast away their
> > > output, unlike similar implementations for other I/O buses.
> > > When they are combined using conditional expressions in the definitions of
> > > outb() and friends, this triggers sparse warnings like:
> > >
> > >       drivers/net/appletalk/cops.c:382:17: error: incompatible types in conditional expression (different base types):
> > >       drivers/net/appletalk/cops.c:382:17:    unsigned char
> > >       drivers/net/appletalk/cops.c:382:17:    void
> > >
> > > Fix this by adding casts to "void".
> > >
> > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> >
> > Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
>
> Thanks!
>
> > > Removing the casts instead causes issues with functions propagating void
> > > return values (return expression in void function), which BTW sparse
> > > complains about, too.
> >
> > We live and learn. I didn't even know that this was valid syntax.
>
> I knew about the syntax, but didn't realize immediately why it was
> done that way.
>
> Initially I thought it was some relic from the "always cast to void
> to make it clear you do not care about the return value"-frenzy, which
> are inside Linux visible mostly in the various "(void)acpi_<foo>(...);"
> calls.  AFAIK these are checked by some external tools.
> In Linux, we have __must_check to annotate the important cases.

I looked at the output of my coccinelle script. To me it looks like
(almost ?) all of the code with "return f(...)" in a function returning
void is just sloppy programming.

In case someone is interested, I attached the script I used below.

Guenter

---
virtual report

@d@
function f;
expression e;
position p;
@@

void f(...)
{
    <...
    return e@p;
    ...>
}

@script:python depends on report@
p << d.p;
f << d.f;
e << d.e;
@@

print "Return in void function %s() at %s:%s: %s" % (f, p[0].file, p[0].line, e)