linux-kernel - Re: [PATCH 2/2] mfd: syscon: request a regmap with raw spinlocks for some devices

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Date:   Wed, 25 Aug 2021 23:24:52 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Mark Brown <broonie@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Lee Jones <lee.jones@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Hou Zhiqiang <Zhiqiang.Hou@....com>,
        Biwen Li <biwen.li@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mfd: syscon: request a regmap with raw spinlocks for
 some devices

On Wed, Aug 25, 2021 at 10:50 PM Vladimir Oltean
<vladimir.oltean@....com> wrote:
>
> This patch solves a ls-extirq irqchip driver bug in a perhaps
> non-intuitive (at least non-localized) way.
>
> The issue is that ls-extirq uses regmap, and due to the fact that it is
> being called by the IRQ core under raw spinlock context, it needs to use
> raw spinlocks itself. So it needs to request raw spinlocks from the
> regmap config.
>
> All is fine so far, except the ls-extirq driver does not manage its own
> regmap, instead it uses syscon_node_to_regmap() to get it from the
> parent syscon (this driver).
>
> Because the syscon regmap is initialized before any of the consumer
> drivers (ls-extirq) probe, we need to know beforehand whether to request
> raw spinlocks or not.
>
> The solution seems to be to check some compatible string. The ls-extirq
> driver probes on quite a few NXP Layerscape SoCs, all with different
> compatible strings. This is potentially fragile and subject to bit rot
> (since the fix is not localized to the ls-extirq driver, adding new
> compatible strings there but not here seems plausible). Anyway, it is
> probably the best we can do without major rework.
>
> Suggested-by: Mark Brown <broonie@...nel.org>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

This should work, but how hard would it be to change the ls-extirq
driver instead to not use the syscon driver at all but make the extirq
driver set up the regmap itself?

Are there any other users of the syscon?

         Arnd