From: Vladimir Oltean <vladimir.oltean@nxp.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Brown <broonie@kernel.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Lee Jones <lee.jones@linaro.org>, Arnd Bergmann <arnd@arndb.de>,
Marc Zyngier <maz@kernel.org>, "Z.Q. Hou" <zhiqiang.hou@nxp.com>,
Biwen Li <biwen.li@nxp.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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
understanding").
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.
next prev parent 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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