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From: Thierry Reding <thierry.reding@gmail.com>
To: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: linux-pwm@vger.kernel.org, narmstrong@baylibre.com,
	linux-kernel@vger.kernel.org, u.kleine-koenig@pengutronix.de,
	linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org, jbrunet@baylibre.com
Subject: Re: [PATCH v2 1/1] pwm: meson: use the spin-lock only to protect register modifications
Date: Thu, 9 May 2019 16:52:42 +0200
Message-ID: <20190509145242.GZ8907@ulmo> (raw)
In-Reply-To: <20190401175748.5376-2-martin.blumenstingl@googlemail.com>

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On Mon, Apr 01, 2019 at 07:57:48PM +0200, 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>
> Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
>  drivers/pwm/pwm-meson.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)

Applied, thanks.

Thierry

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Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-01 17:57 [PATCH v2 0/1] pwm: meson: fix scheduling while atomic issue Martin Blumenstingl
2019-04-01 17:57 ` [PATCH v2 1/1] pwm: meson: use the spin-lock only to protect register modifications Martin Blumenstingl
2019-04-03 11:21   ` Neil Armstrong
2019-05-09 14:52   ` Thierry Reding [this message]

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