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From: Vladimir Oltean <>
To: Thomas Gleixner <>
Cc: Mark Brown <>,
	Rasmus Villemoes <>,
	Lee Jones <>, Arnd Bergmann <>,
	Marc Zyngier <>, "Z.Q. Hou" <>,
	Biwen Li <>,
	Greg Kroah-Hartman <>,
	"Rafael J. Wysocki" <>,
	"" <>
Subject: Re: [PATCH 1/2] regmap: teach regmap to use raw spinlocks if requested in the config
Date: Fri, 27 Aug 2021 16:12:28 +0000	[thread overview]
Message-ID: <20210827161227.4pnaglgctikobpf6@skbuf> (raw)
In-Reply-To: <875yvr3j5c.ffs@tglx>

On Fri, Aug 27, 2021 at 01:01:35AM +0200, Thomas Gleixner wrote:
> On Wed, Aug 25 2021 at 23:50, Vladimir Oltean wrote:
> > It seems reasonable for regmap to have an option use a raw spinlock too,
> > so add that in the config such that drivers can request it.
> What's reasonable about that?
> What exactly prevents the regmap locking to use a raw spinlock
> unconditionally?
> Even for the case where the regmap is not dealing with irq chips it does
> not make any sense to protect low level operations on shared register
> with a regular spinlock. I might be missing something though...

Mark, any comments?

Generally it is said that misusing raw spinlocks has detrimential
performance upon the real-time aspects of the system, and I don't really
have a good feeling for what constitutes misuse vs what is truly justified
(in fact I did start the thread with "apologies for my novice level of

On the other hand, while it does seem a bit too much overhead for
sequences of MMIO reads/writes to be able to be preempted, it doesn't
sound like it would break something either, so...

But I will say that I've tested that and it would solve both my problems
(the stack trace with ls-extirq and the fact that I would like to avoid
reworking the ls-extirq driver too much), as well as problems I never
knew I had: it turns out, armada_37xx_irq_set_type() uses regmap too
(and a sleepable spin lock too - irq_lock). The latter would still have
to be manually patched out.

  reply	other threads:[~2021-08-27 16:12 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25 20:50 [PATCH 0/2] Use raw spinlocks in the ls-extirq driver Vladimir Oltean
2021-08-25 20:50 ` [PATCH 1/2] regmap: teach regmap to use raw spinlocks if requested in the config Vladimir Oltean
2021-08-26 23:01   ` Thomas Gleixner
2021-08-27 16:12     ` Vladimir Oltean [this message]
2021-08-27 19:59       ` Thomas Gleixner
2021-08-30 10:49         ` Vladimir Oltean
2021-08-30 11:02     ` Rasmus Villemoes
2021-08-30 12:42       ` Mark Brown
2021-08-30 12:19     ` Mark Brown
2021-08-30 14:16       ` Thomas Gleixner
2021-09-01 16:05         ` Mark Brown
2021-09-02  8:35           ` Thomas Gleixner
2021-08-25 20:50 ` [PATCH 2/2] mfd: syscon: request a regmap with raw spinlocks for some devices Vladimir Oltean
2021-08-25 21:24   ` Arnd Bergmann
2021-08-25 22:00     ` Vladimir Oltean
2021-08-26  9:24       ` Arnd Bergmann
2021-08-26 13:57         ` Vladimir Oltean
2021-08-26 14:48           ` Arnd Bergmann
2021-09-06  9:18   ` Lee Jones
2021-08-26 12:51 ` (subset) [PATCH 0/2] Use raw spinlocks in the ls-extirq driver Mark Brown

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