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From: Clemens Gruber <clemens.gruber@pqgruber.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: linux-pwm@vger.kernel.org,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Alexandre Belloni" <alexandre.belloni@free-electrons.com>,
	"Shawn Guo" <shawn.guo@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	"Lothar Waßmann" <LW@karo-electronics.de>
Subject: Re: [PATCHv6 0/3] pwm: imx: support output polarity inversion
Date: Mon, 12 Sep 2016 23:12:54 +0200	[thread overview]
Message-ID: <20160912211254.GA4637@archie.localdomain> (raw)
In-Reply-To: <20160912200021.fsnfdgnng4it354g@pengutronix.de>

Hi Uwe,

On Mon, Sep 12, 2016 at 10:00:21PM +0200, Uwe Kleine-König wrote:
> I want that the pwm driver disables its clock on pwm_config(mypwm, 0,
> someperiod) such that the consumer doesn't need to call
> pwm_disable(mypwm) to save power (assuming it's safe to do so, which
> only the pwm provider knows).

I am not sure if this is such a good idea, because there are use cases
where you want to keep the PWM driver enabled the whole time but still
be able to change the duty cycle to 0 for some time without adding
unnecessary delays when changing the duty cycle back to something else.

We have an application where we control fluid valves in a beer
dispensing system through PWMs and these valves are pulsed with
different PWM duty cycles for a short time. In-between the duty cycle
is also 0. For example: Start at 0%, 100ms 90%, 200ms 70%, 300ms 0%,
100ms 90%, and so on..
There it is critical that the change from and to 0 duty cycle is not
delayed by disabling and reenabling the clock.
The oscillator (if there is one) should be up and running, only the duty
cycle should be 0 for a short time.

This would not be possible anymore with your API change, right?

Regards,
Clemens

WARNING: multiple messages have this Message-ID (diff)
From: clemens.gruber@pqgruber.com (Clemens Gruber)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCHv6 0/3] pwm: imx: support output polarity inversion
Date: Mon, 12 Sep 2016 23:12:54 +0200	[thread overview]
Message-ID: <20160912211254.GA4637@archie.localdomain> (raw)
In-Reply-To: <20160912200021.fsnfdgnng4it354g@pengutronix.de>

Hi Uwe,

On Mon, Sep 12, 2016 at 10:00:21PM +0200, Uwe Kleine-K?nig wrote:
> I want that the pwm driver disables its clock on pwm_config(mypwm, 0,
> someperiod) such that the consumer doesn't need to call
> pwm_disable(mypwm) to save power (assuming it's safe to do so, which
> only the pwm provider knows).

I am not sure if this is such a good idea, because there are use cases
where you want to keep the PWM driver enabled the whole time but still
be able to change the duty cycle to 0 for some time without adding
unnecessary delays when changing the duty cycle back to something else.

We have an application where we control fluid valves in a beer
dispensing system through PWMs and these valves are pulsed with
different PWM duty cycles for a short time. In-between the duty cycle
is also 0. For example: Start at 0%, 100ms 90%, 200ms 70%, 300ms 0%,
100ms 90%, and so on..
There it is critical that the change from and to 0 duty cycle is not
delayed by disabling and reenabling the clock.
The oscillator (if there is one) should be up and running, only the duty
cycle should be 0 for a short time.

This would not be possible anymore with your API change, right?

Regards,
Clemens

  reply	other threads:[~2016-09-12 21:12 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-07 13:55 [PATCHv4 0/3] pwm: imx: support output polarity inversion Lothar Waßmann
2014-10-07 13:55 ` Lothar Waßmann
2014-10-07 13:55 ` [PATCHv5 1/3] pwm: print error messages with pr_err() instead of pr_debug() Lothar Waßmann
2014-10-07 13:55   ` Lothar Waßmann
2014-10-07 13:55 ` [PATCHv5 2/3] pwm: make the PWM_POLARITY flag in DTB optional Lothar Waßmann
2014-10-07 13:55   ` Lothar Waßmann
2014-10-09 15:16   ` Thierry Reding
2014-10-09 15:16     ` Thierry Reding
2014-10-10 14:22     ` [PATCHv6 0/3] pwm: imx: support output polarity inversion Lothar Waßmann
2014-10-10 14:22       ` Lothar Waßmann
2014-10-10 14:22       ` [PATCHv6 1/3] pwm: print error messages with pr_err() instead of pr_debug() Lothar Waßmann
2014-10-10 14:22         ` Lothar Waßmann
2014-10-10 14:22       ` [PATCHv6 2/3] pwm: make the PWM_POLARITY flag in DTB optional Lothar Waßmann
2014-10-10 14:22         ` Lothar Waßmann
2014-10-10 14:22       ` [PATCH 3/3] pwm: imx: support output polarity inversion Lothar Waßmann
2014-10-10 14:22         ` Lothar Waßmann
2016-09-08 22:15       ` [PATCHv6 0/3] " Stefan Agner
2016-09-08 22:15         ` Stefan Agner
2016-09-09  7:18         ` Lothar Waßmann
2016-09-09  7:18           ` Lothar Waßmann
2016-09-12 12:45           ` Alexandre Belloni
2016-09-12 12:45             ` Alexandre Belloni
2016-09-12 14:04             ` Uwe Kleine-König
2016-09-12 14:04               ` Uwe Kleine-König
2016-09-12 16:51               ` Stefan Agner
2016-09-12 16:51                 ` Stefan Agner
2016-09-12 20:00                 ` Uwe Kleine-König
2016-09-12 20:00                   ` Uwe Kleine-König
2016-09-12 21:12                   ` Clemens Gruber [this message]
2016-09-12 21:12                     ` Clemens Gruber
2016-09-13  6:45                     ` Uwe Kleine-König
2016-09-13  6:45                       ` Uwe Kleine-König
2016-09-12 13:54           ` Vladimir Zapolskiy
2016-09-12 13:54             ` Vladimir Zapolskiy
2014-10-07 13:55 ` [PATCHv5 3/3] " Lothar Waßmann
2014-10-07 13:55   ` Lothar Waßmann

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