Messages in this thread | | | Date | Mon, 25 Mar 2019 09:48:22 +0100 | From | Uwe Kleine-König <> | Subject | Re: [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications |
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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/ |
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