Messages in this thread | | | Date | Mon, 25 Mar 2019 09:41:53 +0100 | From | Uwe Kleine-König <> | Subject | Re: [PATCH 0/1] pwm: meson: fix scheduling while atomic issue |
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Hello Martin,
On Sun, Mar 24, 2019 at 11:02:16PM +0100, Martin Blumenstingl wrote: > Back in January a "BUG: scheduling while atomic" error showed up during > boot on my Meson8b Odroid-C1 (which uses a PWM regulator as CPU supply). > The call trace comes down to: > __mutex_lock > clk_prepare_lock > clk_core_get_rate > meson_pwm_apply > .. > dev_pm_opp_set_rate > .. > > Jerome has also seen the same problem but from pwm-leds (instead of a > pwm-regulator). He posted a patch which replaces the spinlock with a > mutex. That works. I believe we can optimize this by reducing the time > where the lock is held - that also allows to keep the spin-lock. > > Analyzing this issue helped me understand the pwm-meson driver better. > My plan is to send some cleanups (with the goal of re-using more of the > goodies from the PWM core in the pwm-meson driver) after this single fix > is merged (they can be found here: [1]).
I didn't look over these in detail, but I see an issue that according to the shortlogs isn't addressed: In the .apply callback there is (simplified):
if (!state->enabled) { meson_pwm_disable(meson, pwm->hwpwm); return; }
This results in the wrong output after:
pwm_apply_state(pwm, { .enabled = true, .polarity = PWM_POLARITY_NORMAL, ...}); pwm_apply_state(pwm, { .enabled = false, .polarity = PWM_POLARITY_INVERTED, ...});
because the polarity isn't checked.
If you want to implement further cleanups, my questions and propositions are:
- Is there a publicly available manual for this hardware? If yes, you can add a link to it in the header of the driver.
- Why do you handle reparenting of the PWM's clk in .request? Wouldn't this be more suitable in .apply?
- Does stopping the PWM (i.e. clearing MISC_{A,B}_EN in the MISC_AB register) freeze the output, or is the currently running period completed first? (The latter is the right behaviour.)
- Please point out in the header that for changing period/duty cycle/polarity the hardware must be stopped. (I suggest to apply the style used in https://www.spinics.net/lists/linux-pwm/msg09262.html for some consistency.)
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
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