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

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Message-ID: <b52e7fde-8874-3c53-ca13-7709656b69fb@vivier.eu>
Date:   Tue, 20 Oct 2020 20:42:53 +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 20:32, Greg KH a écrit :
> On Tue, Oct 20, 2020 at 08:19:26PM +0200, Laurent Vivier wrote:
>> 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;
>> ...
> 
> Yup, that would be a good start, but why is the pmac_zilog.h file
> responsible for this?  Shouldn't this be in some arch-specific file
> somewhere?

For m68k, MACH_IS_MAC is defined in arch/m68k/include/asm/setup.h

If I want to define it for any other archs I don't know in which file we
can put it.

But as m68k mac is only sharing drivers with pmac perhaps we can put
this in arch/powerpc/include/asm/setup.h?

Thanks,
Laurent