Messages in this thread | | | Date | Sat, 24 Sep 2016 22:25:02 +0200 | From | Maxime Ripard <> | Subject | Re: [PATCH 1/2] pwm: sunxi: allow the pwm to finish its pulse before disable |
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Hi Oliver,
Sorry for the slow answer.
On Fri, Sep 09, 2016 at 11:01:08AM +0200, Olliver Schinagl wrote: > > > > > *chip, struct pwm_device *pwm) > > > > > spin_lock(&sun4i_pwm->ctrl_lock); > > > > > val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG); > > > > > val &= ~BIT_CH(PWM_EN, pwm->hwpwm); > > > > > + sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG); > > > > > + spin_unlock(&sun4i_pwm->ctrl_lock); > > > > > + > > > > > + /* Allow for the PWM hardware to finish its last > > > > > toggle. > > > > > The pulse > > > > > + * may have just started and thus we should wait a > > > > > full > > > > > period. > > > > > + */ > > > > > + ndelay(pwm_get_period(pwm)); > > > > > > > > Can't that use the ready bit as well? > > > It depends whatever is cheaper. If we disable the pwm, we have to > > > commit that request to hardware first. Then we have to read back > > > the > > > has ready and in the strange situation it is not, wait for it to > > > become > > > ready? > > > > If it works like you were suggesting, yes. > > > > > > > > Also, that would mean we would loop in a spin lock, or keep > > > setting/clearing an additional spinlock to read the ready bit. > > > > You're using a spin_lock, so it's not that bad, but I was just > > suggesting replacing the ndelay. > > If you say the spin_lock + wait for the ready is just as expensive as > the ndelay, or the ndelay is less preferred, then I gladly make the > change;
For the spin_lock part, I was just comparing it to a spin_lock_irqsave, which is pretty expensive since it masks all the interrupts in the system, introducing latencies.
> but I think we need the ndelay for the else where we do not > have the ready flag (A10 or A13 iirc?)
Hmmmm, good point. But that would also apply to your second patch then, wouldn't it?
Maxime
-- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com [unhandled content-type:application/pgp-signature] | |