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Subject: [PATCH v3 3/7] asm-generic: qrwlock: Document the spinlock fairness requirements
Date:   Thu, 14 Apr 2022 15:02:10 -0700
Message-Id: <20220414220214.24556-4-palmer@rivosinc.com>
In-Reply-To: <20220414220214.24556-1-palmer@rivosinc.com>
References: <20220414220214.24556-1-palmer@rivosinc.com>
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Cc:     peterz@infradead.org, mingo@redhat.com,
        Will Deacon <will@kernel.org>, longman@redhat.com,
        boqun.feng@gmail.com, jonas@southpole.se,
        stefan.kristiansson@saunalahti.fi,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>, aou@eecs.berkeley.edu,
        Arnd Bergmann <arnd@arndb.de>, macro@orcam.me.uk,
        Greg KH <gregkh@linuxfoundation.org>,
        sudipm.mukherjee@gmail.com, wangkefeng.wang@huawei.com,
        jszhang@kernel.org, linux-csky@vger.kernel.org,
        linux-kernel@vger.kernel.org, openrisc@lists.librecores.org,
        linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org,
        Palmer Dabbelt <palmer@rivosinc.com>
From:   Palmer Dabbelt <palmer@rivosinc.com>
To:     Arnd Bergmann <arnd@arndb.de>, heiko@sntech.de, guoren@kernel.org,
        shorne@gmail.com
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From: Palmer Dabbelt <palmer@rivosinc.com>

I could only find the fairness requirements documented as the C code,
this calls them out in a comment just to be a bit more explicit.

Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
 include/asm-generic/qrwlock.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 7ae0ece07b4e..24ae09c1db9f 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -2,6 +2,10 @@
 /*
  * Queue read/write lock
  *
+ * These use generic atomic and locking routines, but depend on a fair spinlock
+ * implementation in order to be fair themselves.  The implementation in
+ * asm-generic/spinlock.h meets these requirements.
+ *
  * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
  *
  * Authors: Waiman Long <waiman.long@hp.com>
-- 
2.34.1