linux-kernel - Re: [PATCH v3 6/6] ARM: PWM: add allwinner sun8i R40/T3/V40 PWM support.

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Message-ID: <20181203094908.lga2r56gelaghrej@pengutronix.de>
Date:   Mon, 3 Dec 2018 10:49:08 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Hao Zhang <hao5781286@...il.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com,
        maxime.ripard@...tlin.com, wens@...e.org, mturquette@...libre.com,
        sboyd@...nel.org, thierry.reding@...il.com,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pwm@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v3 6/6] ARM: PWM: add allwinner sun8i R40/T3/V40 PWM
 support.

Hello,

On Mon, Nov 26, 2018 at 10:31:58PM +0100, Uwe Kleine-König wrote:
> > +static int sun8i_pwm_config(struct sun8i_pwm_chip *sun8i_pwm, u8 ch,
> > +			    struct pwm_state *state)
> > +{
> > +[...]
> > +		clk_rate = clk_get_rate(clk);
> > +		val = state->period * clk_rate;
> > +		do_div(val, NSEC_PER_SEC);
> > +		if (val <= 1) {
> > +			dev_err(sun8i_pwm->chip.dev,
> > +				"Period expects a larger value\n");
> > +			return -EINVAL;
> > +		}
> > +
> > +		/* change clock source to "mux-1" */
> > +		clk_disable_unprepare(sun8i_pwm->clk);
> > +		devm_clk_put(sun8i_pwm->chip.dev, sun8i_pwm->clk);
> > +		sun8i_pwm->clk = clk;
> 
> sun8i_pwm is shared for all 8 PWMs, right? So if you assign mux-1 here
> for the second mux, how does this influence the first PWM?

To clearify my question:

after the first pwm is used and enabled (maybe using mux-0) changing
sun8i_pwm->clk for the second pwm is broken because then when the first
pwm is disabled the wrong clock is stopped.

Best regards
Uwe

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