linux-kernel - Re: [PATCH v2] pwm: kconfig: enable kona pwm to be built for cygnus arch

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Date:   Fri, 23 Nov 2018 11:25:38 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Clément Péron <peron.clem@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] pwm: kconfig: enable kona pwm to be built for cygnus
 arch

Hello Clément,

On Fri, Nov 23, 2018 at 10:31:18AM +0100, Clément Péron wrote:
> On Thu, 22 Nov 2018 at 21:05, Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> wrote:
> > Related to this driver I have a set of questions: If the disable
> > callback completed, does the hardware still drive the pin? If yes, would
> > it be possible to disable the pin driver such that the pin gets high-Z?
> > If yes, how?
> 
> The output pin type is configured with the bit "21:16 PWMOUT_TYPE RW
> default 0x3F" in the Control register
> PWM_CONTROL_TYPE_SHIFT macro in the driver
> Datasheets says : "When set to 1 the PWM Output signal will have a
> push/pull type.When set to 0 the PWM Output signal will have an open
> drain output type.Recommend to leave it push/pull type."
> 
> In the driver we actually set push/pull mode for all channels :
> /* Set push/pull for all channels */
> for (chan = 0; chan < kp->chip.npwm; chan++)
> value |= (1 << PWM_CONTROL_TYPE_SHIFT(chan));

So if disabling the output driver was part of the requirements for
.disable the bcm-kona driver could not implement this for both inverted
and uninverted PWMs. (At least not without resorting to pinmuxing.)

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |