Re: [PATCH v4 13/13] riscv: Add qspinlock support

From: Alexandre Ghiti <alex@ghiti.fr>
To: Andrew Jones <ajones@ventanamicro.com>,
	Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Conor Dooley <conor@kernel.org>, Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Andrea Parri <parri.andrea@gmail.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
	Waiman Long <longman@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>, Arnd Bergmann <arnd@arndb.de>,
	Leonardo Bras <leobras@redhat.com>, Guo Ren <guoren@kernel.org>,
	linux-doc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-arch@vger.kernel.org
Subject: Re: [PATCH v4 13/13] riscv: Add qspinlock support
Date: Fri, 2 Aug 2024 10:58:51 +0200	[thread overview]
Message-ID: <0abc375c-61a1-4b8c-bac5-a5dc170c5fb6@ghiti.fr> (raw)
In-Reply-To: <20240801-e773d3752fe8b5484405d404@orel>

On 01/08/2024 12:15, Andrew Jones wrote:
> On Thu, Aug 01, 2024 at 10:43:03AM GMT, Alexandre Ghiti wrote:
> ...
>>>> diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
>>>> index 0655aa5b57b2..bf47cca2c375 100644
>>>> --- a/include/asm-generic/qspinlock.h
>>>> +++ b/include/asm-generic/qspinlock.h
>>>> @@ -136,6 +136,7 @@ static __always_inline bool virt_spin_lock(struct qspinlock *lock)
>>>>   }
>>>>   #endif
>>>>
>>>> +#ifndef __no_arch_spinlock_redefine
>>> I'm not sure what's better/worse, but instead of inventing this
>>> __no_arch_spinlock_redefine thing we could just name all the functions
>>> something like __arch_spin* and then add defines for both to asm/spinlock.h,
>>> i.e.
>>>
>>> #define queued_spin_lock(l) __arch_spin_lock(l)
>>> ...
>>>
>>> #define ticket_spin_lock(l) __arch_spin_lock(l)
>>> ...
>> __arch_spin_lock() would use queued_spin_lock() so that would make an
>> "infinite recursive definition" right? And that would override the
>> "real" queued_spin_lock() implementation too.
>>
>> But maybe I missed something!
>>
> It depends on where the definition is done. It should work if the
> preprocessor expands the implementation of __arch_spin_* before
> evaluating the #define of queued_spin_*. IOW, we just need to put
> the defines after the static inline constructions.

So I have just given it a try, both qspinlock.h and ticket_spinlock.h 
define arch_spin_XXXX(). That triggers a bunch of warnings.

I'll drop this suggestion as I find it harder to understand and because 
of the warnings that would need the introduction of a new preprocessor 
variable (or something else?).  And the solution with 
__no_arch_spinlock_redefine is really straightforward and lightweight.

Thanks,

Alex

>
> Thanks,
> drew
>
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