linux-kernel - Re: [PATCH v1] ASoC: meson: axg-fifo: set option to use raw spinlock

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Message-ID: <04b2b8c5-8b18-4594-9eeb-9971d8cf3786@sirena.org.uk>
Date: Mon, 5 Aug 2024 17:56:22 +0100
From: Mark Brown <broonie@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Jerome Brunet <jbrunet@...libre.com>, linux-rt-users@...r.kernel.org,
	Arseniy Krasnov <avkrasnov@...utedevices.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Kevin Hilman <khilman@...libre.com>,
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
	alsa-devel@...a-project.org, linux-sound@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...rdevices.ru, oxffffaa@...il.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v1] ASoC: meson: axg-fifo: set option to use raw spinlock

On Mon, Aug 05, 2024 at 05:33:09PM +0200, Sebastian Andrzej Siewior wrote:

> I'm not sure if making the lock a raw_spinlock_t solves all the
> problems. The regmap is regmap_mmio so direct memory-access and looks
> simple enough to do so. In regmap_mmio_write() I see clk_enable() and
> and this uses a spinlock_t so we should be back at the same problem.

The clk_enable() is optional, users simply shouldn't use the internal
clock management with devices that it'll cause problems for.

> There might be an additional problem if reg-caching is enabled.

The flat cache is there mostly for the benefit of things accessed from
interrupt context, it guarantees to never do any allocations and doesn't
lock.  You can also use other caches if you ensure that any registers
accessed in interrupt context are already cached so won't trigger any
new allocations.

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