Re: [PATCH v2 1/5] PM: domains: Add GENPD_FLAG_RT_SAFE for PREEMPT_RT

[Krzysztof Kozlowski]

On 04/01/2023 16:45, Ulf Hansson wrote:
> On Mon, 19 Dec 2022 at 16:15, Krzysztof Kozlowski
> <krzysztof.kozlowski@xxxxxxxxxx> wrote:
>>
>> Realtime kernels with PREEMPT_RT must use raw_spinlock_t for domains
>> which are invoked from CPU idle (thus from atomic section).  Example is
>> cpuidle PSCI domain driver which itself is PREEMPT_RT safe, but is being
>> called as part of cpuidle.
> 
> Just so I don't get this wrong, since the cpuidle-psci also calls
> pm_runtime_* functions so it isn't PREEMPT_RT safe, at least not yet?

You are correct. Patch 3 here addresses it by... just not doing runtime
PM. This is a hacky workaround but:
1. I don't have any other idea,
2. It's not a big problem because RT systems are not supposed to have
any CPU idle (one of first things during RT system tuning is to disable
cpuidle).

> 
>>
>> Add a flag allowing a power domain provider to indicate it is RT safe.
>> The flag is supposed to be used with existing GENPD_FLAG_IRQ_SAFE.
>>
>> Cc: Adrien Thierry <athierry@xxxxxxxxxx>
>> Cc: Brian Masney <bmasney@xxxxxxxxxx>
>> Cc: linux-rt-users@xxxxxxxxxxxxxxx
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> 
> For genpd, overall, I think this looks like an okay approach to me.
> Although, let me check the whole series (I need some more time to do
> that) before I give this my blessing.

Sure, we are all have too many mails in inbox. :)

Best regards,
Krzysztof