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From: Nathan Lynch <nathanl@linux.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 16/29] powerpc/rtas: dispatch partition migration
 requests to pseries
In-Reply-To: <874kl1vilh.fsf@mpe.ellerman.id.au>
References: <20201030011805.1224603-1-nathanl@linux.ibm.com>
 <20201030011805.1224603-17-nathanl@linux.ibm.com>
 <874kl1vilh.fsf@mpe.ellerman.id.au>
Date: Fri, 04 Dec 2020 10:04:56 -0600
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Michael Ellerman <mpe@ellerman.id.au> writes:
> Nathan Lynch <nathanl@linux.ibm.com> writes:
>> sys_rtas() cannot call ibm,suspend-me directly in the same way it
>> handles other inputs. Instead it must dispatch the request to code
>> that can first perform the H_JOIN sequence before any call to
>> ibm,suspend-me can succeed. Over time kernel/rtas.c has accreted a fair
>> amount of platform-specific code to implement this.
>>
>> Since a different, more robust implementation of the suspend sequence
>> is now in the pseries platform code, we want to dispatch the request
>> there while minimizing additional dependence on pseries.
>>
>> Use a weak function that only pseries overrides.
>
> Over the years weak functions have caused their fair share of problems.
>
> There are cases where they are the cleanest option, but for intra-arch
> code like this I think and ifdef is much simpler.

Fair enough, I wasn't all that confident about this anyway.


>> diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
>> index fdefe6a974eb..be0fc2536673 100644
>> --- a/arch/powerpc/include/asm/rtas.h
>> +++ b/arch/powerpc/include/asm/rtas.h
>> @@ -260,6 +260,7 @@ extern int rtas_suspend_cpu(struct rtas_suspend_me_data *data);
>>  extern int rtas_suspend_last_cpu(struct rtas_suspend_me_data *data);
>>  int rtas_ibm_suspend_me_unsafe(u64 handle);
>>  int rtas_ibm_suspend_me(int *fw_status);
>> +int rtas_syscall_dispatch_ibm_suspend_me(u64 handle);
>
> ie. we'd just do:
>
> #ifdef CONFIG_PPC_PSERIES
> int rtas_syscall_dispatch_ibm_suspend_me(u64 handle);
> #else
> int rtas_syscall_dispatch_ibm_suspend_me(u64 handle)
> {
> 	return -EINVAL;
> }
> #endif

Yep will do.