Realtime support for 5.10 on RISC-V -- not there

Realtime support for 5.10 on RISC-V -- not there

[Pavel Machek]

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Hi!

In rt wiki, RISC-V is not listed as supported. 

https://rt.wiki.kernel.org/index.php/CONFIG_PREEMPT_RT_Patch#Platforms_Tested_and_in_Use_with_CONFIG_PREEMPT_RT

That may be outdated, but it does not have corresponding config option
in 5.10.

pavel@duo:~/cip/10$ grep -ri ARCH_SUPPORTS_RT arch/
arch/powerpc/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/arm/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/x86/Kconfig:	select ARCH_SUPPORTS_RT
arch/arm64/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
arch/Kconfig:config ARCH_SUPPORTS_RT
pavel@duo:~/cip/10$

I do not think we can or want to support realtime on RISC-V at the
moment.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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Re: Realtime support for 5.10 on RISC-V -- not there

[Jan Kiszka]

On 02.09.22 11:57, Pavel Machek wrote:
> Hi!
> 
> In rt wiki, RISC-V is not listed as supported. 
> 
> https://rt.wiki.kernel.org/index.php/CONFIG_PREEMPT_RT_Patch#Platforms_Tested_and_in_Use_with_CONFIG_PREEMPT_RT
> 
> That may be outdated, but it does not have corresponding config option
> in 5.10.
> 
> pavel@duo:~/cip/10$ grep -ri ARCH_SUPPORTS_RT arch/
> arch/powerpc/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
> arch/arm/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
> arch/x86/Kconfig:	select ARCH_SUPPORTS_RT
> arch/arm64/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
> arch/Kconfig:config ARCH_SUPPORTS_RT
> pavel@duo:~/cip/10$

Thanks for checking! Same situation in 6.0.y-rt, it seems.

> 
> I do not think we can or want to support realtime on RISC-V at the
> moment.

In fact, we couldn't realistically commit to such a non-existing feature
/wrt long-term support.

If there is interest in enabling this, we can start a development effort
in upstream. But if that could then be backportable only to the next CIP
kernel, would even be open.

Jan

-- 
Siemens AG, Technology
Competence Center Embedded Linux

Re: Realtime support for 5.10 on RISC-V -- not there

[Jan Kiszka]

On 02.09.22 16:47, Jan Kiszka wrote:
> On 02.09.22 11:57, Pavel Machek wrote:
>> Hi!
>>
>> In rt wiki, RISC-V is not listed as supported. 
>>
>> https://rt.wiki.kernel.org/index.php/CONFIG_PREEMPT_RT_Patch#Platforms_Tested_and_in_Use_with_CONFIG_PREEMPT_RT
>>
>> That may be outdated, but it does not have corresponding config option
>> in 5.10.
>>
>> pavel@duo:~/cip/10$ grep -ri ARCH_SUPPORTS_RT arch/
>> arch/powerpc/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
>> arch/arm/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
>> arch/x86/Kconfig:	select ARCH_SUPPORTS_RT
>> arch/arm64/Kconfig:	select ARCH_SUPPORTS_RT if HAVE_POSIX_CPU_TIMERS_TASK_WORK
>> arch/Kconfig:config ARCH_SUPPORTS_RT
>> pavel@duo:~/cip/10$
> 
> Thanks for checking! Same situation in 6.0.y-rt, it seems.
> 
>>
>> I do not think we can or want to support realtime on RISC-V at the
>> moment.
> 
> In fact, we couldn't realistically commit to such a non-existing feature
> /wrt long-term support.
> 
> If there is interest in enabling this, we can start a development effort
> in upstream. But if that could then be backportable only to the next CIP
> kernel, would even be open.
> 

http://lists.infradead.org/pipermail/linux-riscv/2022-August/018823.html

Maybe there is a chance to have this in 6.1-rt so that 6.1-cip-rt can
pick it up.

Jan

-- 
Siemens AG, Technology
Competence Center Embedded Linux

Re: Realtime support for 5.10 on RISC-V -- not there

[Pavel Machek]

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Hi!

> >> I do not think we can or want to support realtime on RISC-V at the
> >> moment.
> > 
> > In fact, we couldn't realistically commit to such a non-existing feature
> > /wrt long-term support.
> > 
> > If there is interest in enabling this, we can start a development effort
> > in upstream. But if that could then be backportable only to the next CIP
> > kernel, would even be open.
> > 
> 
> http://lists.infradead.org/pipermail/linux-riscv/2022-August/018823.html
> 
> Maybe there is a chance to have this in 6.1-rt so that 6.1-cip-rt can
> pick it up.

Yes, that can happen. Plus, the patches are surprisingly small, so
maybe -stable-rt tree picks them up even if they miss 6.1.

OTOH maybe if would be good to have feedback "is someone using -rt on
riscv, and if so, on what hardware"?

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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RE: Realtime support for 5.10 on RISC-V -- not there

[Chris Paterson]

Hello Pavel,

> From: Pavel Machek <pavel@denx.de>
> Sent: 05 October 2022 19:26
> 
> Hi!
> 
> > >> I do not think we can or want to support realtime on RISC-V at the
> > >> moment.
> > >
> > > In fact, we couldn't realistically commit to such a non-existing feature
> > > /wrt long-term support.
> > >
> > > If there is interest in enabling this, we can start a development effort
> > > in upstream. But if that could then be backportable only to the next CIP
> > > kernel, would even be open.
> > >
> >
> > http://lists.infradead.org/pipermail/linux-riscv/2022-August/018823.html
> >
> > Maybe there is a chance to have this in 6.1-rt so that 6.1-cip-rt can
> > pick it up.
> 
> Yes, that can happen. Plus, the patches are surprisingly small, so
> maybe -stable-rt tree picks them up even if they miss 6.1.
> 
> OTOH maybe if would be good to have feedback "is someone using -rt on
> riscv, and if so, on what hardware"?

We're not currently using- rt with our RZ/Five risc-v SoC.
However, if CIP started supporting it we would integrate it into our BSP,
as we have done with our other (Arm) products based on the CIP kernel.

Kind regards, Chris

> 
> Best regards,
> 								Pavel
> --
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany