linux-kernel - Re: [PATCH v8 2/2] pwm: sifive: Add a driver for SiFive SoC PWM

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Date:   Mon, 11 Mar 2019 14:29:22 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Yash Shah <yash.shah@...ive.com>
Cc:     mark.rutland@....com, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, Palmer Dabbelt <palmer@...ive.com>,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        Sachin Ghadi <sachin.ghadi@...ive.com>,
        Thierry Reding <thierry.reding@...il.com>,
        kernel@...gutronix.de, Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v8 2/2] pwm: sifive: Add a driver for SiFive SoC PWM

Hello,

On Mon, Mar 11, 2019 at 05:10:17PM +0530, Yash Shah wrote:
> On Fri, Mar 8, 2019 at 5:27 PM Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> wrote:
> > On Fri, Mar 08, 2019 at 04:59:36PM +0530, Yash Shah wrote:
> > > On Thu, Mar 7, 2019 at 8:57 PM Uwe Kleine-König
> > > <u.kleine-koenig@...gutronix.de> wrote:
> > > > > +     if (state->period != cur_state.period) {
> > > >
> > > > Did you test this with more than one consumer? For sure the following
> > > > should work:
> > > >
> > > >         pwm1 = pwm_get(.. the first ..);
> > > >         pwm_apply_state(pwm1, { .enabled = true, .period = 10000000, .... });
> > > >
> > > >         pwm2 = pwm_get(.. the second ..);
> > > >         pwm_apply_state(pwm2, { .enabled = true, .period = 10000000, .... });
> > > >
> > > > but for the second pwm_apply_state() run state->period is likely not
> > > > exactly 10000000.
> > >
> > > Yes, I have tested multiple consumers using sysfs interface. It is working.
> >
> > Can you provide details about your testing here? What is the parent clk
> > rate? Which settings did you test? Can you confirm my claim that the
> > above sequence would fail or point out my error in reasoning?
> >
> 
> I have tested on HiFive Unleashed board using sysfs interface.
> Parent clk rate is around 512 Mhz.
> I have tested scenarios as you mentioned above with various period and
> duty_cycle values.
> 
> After considering your below suggestion,
>  | To get the result independent of the prior configuration you better use
>  | the real targeted period length as input instead of the last configured
>  | approximation
> I will introduce approx_period feild, which will be used as the
> targeted period length.
> Also, in pwm_sifive_get_state, I will make below change
> - state->period = pwm->real_period;
> + state->period = pwm->approx_period.
> So with this change in place, I believe the cur_state.period for the
> second pwm_apply_state() above (pwm2) will be exactly 10000000

I don't understand your intention completely. Just send a new patch
round, then I will gladly take another look.

Best regards
Uwe

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