From: Peter Zijlstra <peterz@infradead.org>
To: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>,
linux-mips@linux-mips.org,
Adam Buchbinder <adam.buchbinder@gmail.com>,
Arnd Bergmann <arnd@arndb.de>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
linux-kernel@vger.kernel.org,
"Michael S. Tsirkin" <mst@redhat.com>,
Markos Chandras <markos.chandras@imgtec.com>,
Paul Burton <paul.burton@imgtec.com>
Subject: Re: [PATCH 06/10] MIPS: pm-cps: Use MIPS standard lightweight ordering barrier
Date: Wed, 31 Aug 2016 16:28:21 +0200 [thread overview]
Message-ID: <20160831142821.GF10138@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <4c91d6c3-8141-594a-562c-96ea56776d2e@imgtec.com>
On Wed, Aug 31, 2016 at 02:36:26PM +0100, Matt Redfearn wrote:
>
> The code previously had 0x10 as a magic number, this patch just replaces
> that with a #defined name. The value is documented in the MIPS64 instruction
> set manual, https://imgtec.com/?do-download=4302, table 6.5.
>
> This sync type has been standard since MIPSr2. That document also states
> that "If an implementation does not use one of these non-zero values to
> define a different synchronization behavior, then that non-zero value of
> stype must act the same as stype zero completion barrier." As such,
> stype_ordering can always be set to this sync type rather than setting it
> only for certain CPUs.
Right. We all had a bunch of fun trying to decode that manual a while
back, and IIRC were left with a bunch of questions on what it all meant
in 3+ CPU scenarios.
In anycase, not sure why I was Cc'ed to this patch, but in general I
have low confidence in barrier patches that lack lots of detail. And the
code in question has woefully inadequate comments:
/* Ordering barrier */
uasm_i_sync(&p, stype_ordering);
Order what against what and why? Is my first question. A comment really
should explain.
In any case, you've removed the only (runtime) assignment to the
variable, it can become 'const'.
next prev parent reply other threads:[~2016-08-31 14:28 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-31 10:44 [PATCH 00/10] MIPS CPC fixup and CPU Idle for MIPSr6 CPUs Matt Redfearn
2016-08-31 10:44 ` [PATCH 01/10] MIPS: CPC: Convert bare 'unsigned' to 'unsigned int' Matt Redfearn
2016-08-31 10:44 ` [PATCH 02/10] MIPS: CPC: Avoid lock when MIPS CM >= 3 is present Matt Redfearn
2016-08-31 10:44 ` [PATCH 03/10] MIPS: pm-cps: Change FSB workaround to CPU blacklist Matt Redfearn
2016-08-31 10:44 ` [PATCH 04/10] MIPS: pm-cps: Remove I6400 sync types Matt Redfearn
2016-08-31 10:44 ` [PATCH 05/10] MIPS: pm-cps: Add P6600 implementation lightweight " Matt Redfearn
2016-08-31 10:44 ` [PATCH 06/10] MIPS: pm-cps: Use MIPS standard lightweight ordering barrier Matt Redfearn
2016-08-31 11:48 ` Peter Zijlstra
2016-08-31 13:36 ` Matt Redfearn
2016-08-31 14:28 ` Peter Zijlstra [this message]
2016-08-31 15:49 ` Matt Redfearn
2016-08-31 10:44 ` [PATCH 07/10] MIPS: pm-cps: Add MIPSr6 CPU support Matt Redfearn
2016-08-31 10:44 ` [PATCH 08/10] MIPS: pm-cps: Support CM3 changes to Coherence Enable Register Matt Redfearn
2016-08-31 10:44 ` [PATCH 09/10] MIPS: SMP: Wrap call to mips_cpc_lock_other in mips_cm_lock_other Matt Redfearn
2016-08-31 10:44 ` [PATCH 10/10] cpuidle: cpuidle-cps: Enable use with MIPSr6 CPUs Matt Redfearn
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