Subject: Re: [PATCH v4 05/13] powerpc/rtas: Facilitate high-level call sequences

From: Michael Ellerman <[email-masked]>
Date: Wed, 29 Nov 2023 09:30:43 +1100

Nathan Lynch via B4 Relay <[email-masked]>
writes:
> From: Nathan Lynch <[email-masked]>
>
> On RTAS platforms there is a general restriction that the OS must not
> enter RTAS on more than one CPU at a time. This low-level
> serialization requirement is satisfied by holding a spin
> lock (rtas_lock) across most RTAS function invocations.
...
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 1fc0b3fffdd1..52f2242d0c28 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -581,6 +652,28 @@ static const struct rtas_function *rtas_token_to_function(s32 token)
>  	return NULL;
>  }
>  
> +static void __rtas_function_lock(struct rtas_function *func)
> +{
> +	if (func && func->lock)
> +		mutex_lock(func->lock);
> +}

This is obviously going to defeat most static analysis tools. I assume
lockdep is OK with it though?

cheers