From: Maxime Ripard <maxime.ripard@free-electrons.com>
To: Olliver Schinagl <oliver@schinagl.nl>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>,
Thierry Reding <thierry.reding@gmail.com>,
Chen-Yu Tsai <wens@csie.org>,
linux-pwm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] pwm: sunxi: allow the pwm to finish its pulse before disable
Date: Tue, 27 Sep 2016 22:16:28 +0200 [thread overview]
Message-ID: <20160927201628.GB9084@lukather> (raw)
In-Reply-To: <1474879585.6096.33.camel@schinagl.nl>
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Hi,
On Mon, Sep 26, 2016 at 10:46:25AM +0200, Olliver Schinagl wrote:
> > 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.
>
> so spin_lock is very expensive and we should avoid if we can?
spin_lock_irqsave, if possible, yes.
> > > 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?
> yeah, you would have an if/else for the case of !hasready.
>
> this is what i've been dabbling in the train last week, but haven't
> thought it through yet, let alone tested it:
>
>
> + if (!(sun4i_pwm->data->has_rdy))
> + ndelay(pwm_get_period(pwm));
> + else
> + do {
> + spin_lock(&sun4i_pwm->ctrl_lock);
> + val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> + spin_unlock(&sun4i_pwm->ctrl_lock);
> + } while (!(val & PWM_RDY(pwm->hwpwm)))
>
> Here I assumed the spin_lock is cheap to make, expensive to hold for
> long, e.g. reducing the length the spin-lock is active for. the
> alternative was to remove the spin_lock here, and remove unlock-lock
> before-after this block where you basically get a very long lasting
> spin_lock, the alternative.
If you're only reading, why do you need to take the lock?
You probbaly want to have a timeout too.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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next prev parent reply other threads:[~2016-09-27 20:16 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-25 17:50 [PATCHv2 0/2] pwm: sunxi: give the pwm IP block more time Olliver Schinagl
2016-08-25 17:50 ` [PATCH 1/2] pwm: sunxi: allow the pwm to finish its pulse before disable Olliver Schinagl
2016-08-26 22:19 ` Maxime Ripard
2016-09-06 7:12 ` Olliver Schinagl
2016-09-06 19:51 ` Maxime Ripard
2016-09-09 9:01 ` Olliver Schinagl
2016-09-24 20:25 ` Maxime Ripard
2016-09-26 8:46 ` Olliver Schinagl
2016-09-27 20:16 ` Maxime Ripard [this message]
[not found] ` <afcb938d-d2df-4740-6c85-cdf2766f671c@schinagl.nl>
2016-12-12 12:24 ` Maxime Ripard
2017-01-03 15:59 ` Olliver Schinagl
2017-01-03 16:55 ` Alexandre Belloni
2017-01-04 6:36 ` Thierry Reding
2016-09-23 14:02 ` [1/2] " Jonathan Liu
2016-09-23 14:03 ` Olliver Schinagl
2017-05-05 1:54 ` Jonathan Liu
2016-08-25 17:50 ` [PATCH 2/2] pwm: sunxi: Yield some time to the pwm-block to become ready Olliver Schinagl
2016-08-26 22:25 ` Maxime Ripard
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