linux-kernel - Re: [PATCH V3 -next] powerpc: kernel/time.c

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Date:   Wed, 24 Mar 2021 10:43:44 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        He Ying <heying24@...wei.com>
Cc:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        a.zummo@...ertech.it, npiggin@...il.com, msuchanek@...e.de,
        tglx@...utronix.de, peterz@...radead.org, geert@...ux-m68k.org,
        geert+renesas@...der.be, kernelfans@...il.com, frederic@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-rtc@...r.kernel.org
Subject: Re: [PATCH V3 -next] powerpc: kernel/time.c - cleanup warnings



Le 24/03/2021 à 10:29, Alexandre Belloni a écrit :
> On 24/03/2021 05:09:39-0400, He Ying wrote:
>> We found these warnings in arch/powerpc/kernel/time.c as follows:
>> warning: symbol 'decrementer_max' was not declared. Should it be static?
>> warning: symbol 'rtc_lock' was not declared. Should it be static?
>> warning: symbol 'dtl_consumer' was not declared. Should it be static?
>>
>> Declare 'decrementer_max' in powerpc asm/time.h.
>> Include linux/mc146818rtc.h in powerpc kernel/time.c where 'rtc_lock'
>> is declared. And remove duplicated declaration of 'rtc_lock' in powerpc
>> platforms/chrp/time.c because it has included linux/mc146818rtc.h.
>> Move 'dtl_consumer' definition behind "include <asm/dtl.h>" because it
>> is declared there.
>>
>> Reported-by: Hulk Robot <hulkci@...wei.com>
>> Signed-off-by: He Ying <heying24@...wei.com>
>> ---
>> V2:
>> - Instead of including linux/mc146818rtc.h in powerpc kernel/time.c, declare
>>    rtc_lock in powerpc asm/time.h.
>> V3:
>> - Recover to V1, that is including linux/mc146818rtc.h in powerpc
>>    kernel/time.c. And remove duplicated declaration of 'rtc_lock' in powerpc
>>    platforms/chrp/time.c because it has included linux/mc146818rtc.h.
>>
>>   arch/powerpc/include/asm/time.h    | 1 +
>>   arch/powerpc/kernel/time.c         | 9 ++++-----
>>   arch/powerpc/platforms/chrp/time.c | 2 --
>>   3 files changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
>> index 8dd3cdb25338..2cd2b50bedda 100644
>> --- a/arch/powerpc/include/asm/time.h
>> +++ b/arch/powerpc/include/asm/time.h
>> @@ -22,6 +22,7 @@ extern unsigned long tb_ticks_per_jiffy;
>>   extern unsigned long tb_ticks_per_usec;
>>   extern unsigned long tb_ticks_per_sec;
>>   extern struct clock_event_device decrementer_clockevent;
>> +extern u64 decrementer_max;
>>   
>>   
>>   extern void generic_calibrate_decr(void);
>> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
>> index b67d93a609a2..ac81f043bf49 100644
>> --- a/arch/powerpc/kernel/time.c
>> +++ b/arch/powerpc/kernel/time.c
>> @@ -55,8 +55,9 @@
>>   #include <linux/sched/cputime.h>
>>   #include <linux/sched/clock.h>
>>   #include <linux/processor.h>
>> -#include <asm/trace.h>
>> +#include <linux/mc146818rtc.h>
> 
> I'm fine with that but I really think my suggestion to make the rtc_lock
> local to the platforms was better because it is only used to synchronize
> between concurrent invocations of chrp_set_rtc_time or
> maple_set_rtc_time. The rtc core will never do that and the only case
> would be concurrent calls to rtc_ops.set_time and
> update_persistent_clock64 (which should also be removed at some point).

I agree but I think it must be done carefully. If the lock is local to the driver really and without 
a link with the RTC core, then the lock var should probably be static. But then we'll have name 
conflict with the global rtc_lock which is declared in <linux/mc146818rtc.h>

All this is not easy, and I like your idea in the other mail to really clean up the rtc core and 
remove this global rtc_lock completely.

For the time being I guess the fix provided by this patch is just semantic and is just fine as is, 
as there is no real bug behind the messages from sparse.

Christophe