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

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Date:   Tue, 20 Oct 2020 20:19:26 +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 19:37, Greg KH a écrit :
> 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
I would be happy to do the same.

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

I don't know.

Do you mean something like:

drivers/tty/serial/pmac_zilog.h
...
#ifndef MACH_IS_MAC
#define MACH_IS_MAC (0)
#endif
...

drivers/tty/serial/pmac_zilog.c
...
static int __init pmz_console_init(void)
{
        if (!MACH_IS_MAC)
                return -ENODEV;
...

Thanks,
Laurent