[PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Christophe Leroy]

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(-)

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

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Michael Ellerman]

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.

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

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Christophe Leroy]

Le 26/08/2019 à 13:41, Michael Ellerman a écrit :
> 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.

Euh ... yes OK, why not. And that would help simplify many places in the 
code. I can propose something in that direction, but it will be a bigger 
change.


> 
> 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.

However this patch doesn't complicate things more than it was with 
cpu_has_feature() which does exactly the same but using static keys, 
does it ?

Christophe


> 
> 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

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Segher Boessenkool]

On Mon, Aug 26, 2019 at 09:41:39PM +1000, Michael Ellerman wrote:
> 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.

Or you could remove 601 support altogether?


Segher

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Benjamin Herrenschmidt]

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...

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

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Christophe Leroy]

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

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Michael Ellerman]

Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:

> 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...

Paul said his still booted recently.

cheers

Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

[Michael Ellerman]

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> Le 26/08/2019 à 13:41, Michael Ellerman a écrit :
>> 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.
>
> Euh ... yes OK, why not. And that would help simplify many places in the 
> code. I can propose something in that direction, but it will be a bigger 
> change.

Thanks.

>> 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.
>
> However this patch doesn't complicate things more than it was with 
> cpu_has_feature() which does exactly the same but using static keys, 
> does it ?

It's more complicated in that it's not using cpu_has_feature() it's
doing some custom thing that is not used anywhere else. But yeah I guess
it's not much extra complication.

cheers