linux-kernel - Re: [PATCH] serial: pmac_zilog: don't init if zilog is not available

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Date:   Tue, 20 Oct 2020 19:37:45 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Laurent Vivier <laurent@...ier.eu>
Cc:     linux-kernel@...r.kernel.org, Joshua Thompson <funaho@...ai.org>,
        linux-serial@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-m68k@...ts.linux-m68k.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] serial: pmac_zilog: don't init if zilog is not available

On Tue, Oct 20, 2020 at 06:37:41PM +0200, Laurent Vivier wrote:
> Le 20/10/2020 à 18:28, Greg KH a écrit :
> > On Tue, Oct 20, 2020 at 06:23:03PM +0200, Laurent Vivier wrote:
> >> We can avoid to probe for the Zilog device (and generate ugly kernel warning)
> >> if kernel is built for Mac but not on a Mac.
> >>
> >> Signed-off-by: Laurent Vivier <laurent@...ier.eu>
> >> ---
> >>  drivers/tty/serial/pmac_zilog.c | 11 +++++++++++
> >>  1 file changed, 11 insertions(+)
> >>
> >> diff --git a/drivers/tty/serial/pmac_zilog.c b/drivers/tty/serial/pmac_zilog.c
> >> index 063484b22523..d1d2e55983c3 100644
> >> --- a/drivers/tty/serial/pmac_zilog.c
> >> +++ b/drivers/tty/serial/pmac_zilog.c
> >> @@ -1867,6 +1867,12 @@ static struct platform_driver pmz_driver = {
> >>  static int __init init_pmz(void)
> >>  {
> >>  	int rc, i;
> >> +
> >> +#ifdef CONFIG_MAC
> >> +	if (!MACH_IS_MAC)
> >> +		return -ENODEV;
> >> +#endif
> > 
> > Why is the #ifdef needed?
> > 
> > We don't like putting #ifdef in .c files for good reasons.  Can you make
> > the api check for this work with and without that #ifdef needed?
> 
> The #ifdef is needed because this file can be compiled for PowerMac and
> m68k Mac. For PowerMac, the MACH_IS_MAC is not defined, so we need the
> #ifdef.
> 
> We need the MAC_IS_MAC because the same kernel can be used with several
> m68k machines, so the init_pmz can be called on a m68k machine without
> the zilog device (it's a multi-targets kernel).
> 
> You can check it's the good way to do by looking inside:
> 
>     drivers/video/fbdev/valkyriefb.c +317
>     drivers/macintosh/adb.c +316
> 
> That are two files used by both, mac and pmac.

Why not fix it to work properly like other arch checks are done?

Put it in a .h file and do the #ifdef there.  Why is this "special"?

thanks,

greg k-h