linux-kernel - Re: [PATCH 1/2] regulator: core: Sleep (not delay) in set

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Message-ID: <Yl3rNeaYTz0CPjmL@google.com>
Date:   Mon, 18 Apr 2022 15:50:29 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] regulator: core: Sleep (not delay) in set_voltage()

On Mon, Apr 18, 2022 at 02:12:39PM -0700, Brian Norris wrote:
> These delays can be relatively large (e.g., hundreds of microseconds on
> RK3399 Gru systems). Per Documentation/timers/timers-howto.rst, that
> should usually use a sleeping delay. Let's use fsleep() to handle both
> large and small delays appropriately. This avoids burning a bunch of CPU
> time and hurting scheduling latencies when hitting regulators a lot
> (e.g., during cpufreq).
> 
> The sleep vs. delay issue choice has been made differently over time --
> early versions of RK3399 Gru PWM-regulator support used usleep_range()
> in pwm-regulator.c. More of this got moved into the regulator core,
> in commits like:
> 
> 73e705bf81ce regulator: core: Add set_voltage_time op
> 
> At the same time, the sleep turned into a delay.
> 
> It's OK to sleep here, as we aren't in an atomic contexts. (All our
> callers grab various mutexes already.)
> 
> Signed-off-by: Brian Norris <briannorris@...omium.org>

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>