From mboxrd@z Thu Jan 1 00:00:00 1970 From: maxime.ripard@free-electrons.com (Maxime Ripard) Date: Sat, 24 Sep 2016 22:25:02 +0200 Subject: [PATCH 1/2] pwm: sunxi: allow the pwm to finish its pulse before disable In-Reply-To: <1473411668.731.75.camel@schinagl.nl> References: <1472147411-30424-1-git-send-email-oliver@schinagl.nl> <1472147411-30424-2-git-send-email-oliver@schinagl.nl> <20160826221900.GG3165@lukather> <1473145976.731.20.camel@schinagl.nl> <20160906195149.GJ9040@lukather> <1473411668.731.75.camel@schinagl.nl> Message-ID: <20160924202502.GF16901@lukather> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: not available URL: