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

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Message-ID: <468bbbef-4745-3b16-b6f4-30b46ebcdc33@vivier.eu>
Date:   Tue, 20 Oct 2020 18:37:41 +0200
From:   Laurent Vivier <laurent@...ier.eu>
To:     Greg KH <gregkh@...uxfoundation.org>
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

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.

Thanks,
Laurent