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SubjectRe: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.
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Le 26/08/2019 à 15:25, Benjamin Herrenschmidt a écrit :
> On Mon, 2019-08-26 at 21:41 +1000, Michael Ellerman wrote:
>> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>>> sched_clock(), used by printk(), calls __USE_RTC() to know
>>> whether to use realtime clock or timebase.
>>>
>>> __USE_RTC() uses cpu_has_feature() which is initialised by
>>> machine_init(). Before machine_init(), __USE_RTC() returns true,
>>> leading to a program check exception on CPUs not having realtime
>>> clock.
>>>
>>> In order to be able to use printk() earlier, use feature fixup.
>>> Feature fixups are applies in early_init(), enabling the use of
>>> printk() earlier.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>>> ---
>>> arch/powerpc/include/asm/time.h | 9 ++++++++-
>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> The other option would be just to make this a compile time decision, eg.
>> add CONFIG_PPC_601 and use that to gate whether we use RTC.
>>
>> Given how many 601 users there are, maybe 1?, I think that would be a
>> simpler option and avoids complicating the code / binary for everyone
>> else.
>
> Didn't we ditch 601 support years ago anyway ? We had workaround we
> threw out I think...

There are still workarounds for 601 in the kernel, for exemple (in
arch/powerpc/include/asm/ppc_asm.h)

/* various errata or part fixups */
#ifdef CONFIG_PPC601_SYNC_FIX
#define SYNC \
BEGIN_FTR_SECTION \
sync; \
isync; \
END_FTR_SECTION_IFSET(CPU_FTR_601)
#define SYNC_601 \
BEGIN_FTR_SECTION \
sync; \
END_FTR_SECTION_IFSET(CPU_FTR_601)
#define ISYNC_601 \
BEGIN_FTR_SECTION \
isync; \
END_FTR_SECTION_IFSET(CPU_FTR_601)
#else
#define SYNC
#define SYNC_601
#define ISYNC_601
#endif

But if you think we can get rid of 601 completely, I'm happy with that.

Christophe


>
> Cheers,
> Ben.
>
>> cheers
>>
>>> diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
>>> index 54f4ec1f9fab..3455cb54c333 100644
>>> --- a/arch/powerpc/include/asm/time.h
>>> +++ b/arch/powerpc/include/asm/time.h
>>> @@ -42,7 +42,14 @@ struct div_result {
>>> /* Accessor functions for the timebase (RTC on 601) registers. */
>>> /* If one day CONFIG_POWER is added just define __USE_RTC as 1 */
>>> #ifdef CONFIG_PPC_BOOK3S_32
>>> -#define __USE_RTC() (cpu_has_feature(CPU_FTR_USE_RTC))
>>> +static inline bool __USE_RTC(void)
>>> +{
>>> + asm_volatile_goto(ASM_FTR_IFCLR("nop;", "b %1;", %0) ::
>>> + "i" (CPU_FTR_USE_RTC) :: l_use_rtc);
>>> + return false;
>>> +l_use_rtc:
>>> + return true;
>>> +}
>>> #else
>>> #define __USE_RTC() 0
>>> #endif
>>> --
>>> 2.13.3

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