From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: thierry.reding@gmail.com, narmstrong@baylibre.com,
jbrunet@baylibre.com, linux-pwm@vger.kernel.org,
linux-amlogic@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications
Date: Mon, 25 Mar 2019 09:48:22 +0100 [thread overview]
Message-ID: <20190325084822.ozixel6bzi6xiw67@pengutronix.de> (raw)
In-Reply-To: <20190324220217.15813-2-martin.blumenstingl@googlemail.com>
Hello,
On Sun, Mar 24, 2019 at 11:02:17PM +0100, Martin Blumenstingl wrote:
> Holding the spin-lock for all of the code in meson_pwm_apply() can
> result in a "BUG: scheduling while atomic". This can happen because
> clk_get_rate() (which is called from meson_pwm_calc()) may sleep.
> Only hold the spin-lock when modifying registers to solve this.
>
> The reason why we need a spin-lock in the driver is because the
> REG_MISC_AB register is shared between the two channels provided by one
> PWM controller. The only functions where REG_MISC_AB is modified are
> meson_pwm_enable() and meson_pwm_disable() so the register reads/writes
> in there need to be protected by the spin-lock.
>
> The original code also used the spin-lock to protect the values in
> struct meson_pwm_channel. This could be necessary if two consumers can
> use the same PWM channel. However, PWM core doesn't allow this so we
> don't need to protect the values in struct meson_pwm_channel with a
> lock.
>
> Fixes: 211ed630753d2f ("pwm: Add support for Meson PWM Controller")
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Looks right.
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Bonus points for adding a comment to struct meson_pwm::lock. Something
like:
/*
* Protects register access to the MISC_AB register that is
* shared between the two PWMs.
*/
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
next prev parent reply other threads:[~2019-03-25 8:48 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-24 22:02 [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Martin Blumenstingl
2019-03-24 22:02 ` [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications Martin Blumenstingl
2019-03-25 8:48 ` Uwe Kleine-König [this message]
2019-03-25 8:41 ` [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Uwe Kleine-König
2019-03-25 8:50 ` Uwe Kleine-König
2019-03-25 17:41 ` Martin Blumenstingl
2019-03-25 20:07 ` Uwe Kleine-König
2019-03-26 20:05 ` Martin Blumenstingl
2019-03-30 19:29 ` Martin Blumenstingl
2019-03-31 18:47 ` Uwe Kleine-König
2019-04-01 7:25 ` Neil Armstrong
2019-03-26 9:06 ` Neil Armstrong
2019-03-26 10:54 ` Uwe Kleine-König
2019-03-25 9:35 ` Jerome Brunet
2019-03-25 18:04 ` Martin Blumenstingl
2019-03-26 8:37 ` Jerome Brunet
2019-03-26 8:57 ` Neil Armstrong
2019-03-26 20:16 ` Martin Blumenstingl
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