linux-kernel - Re: [PATCH v2 1/3] pwm: sun4i: improve hardware read out

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Date:   Wed, 31 May 2017 22:13:55 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Olliver Schinagl <o.schinagl@...imaker.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Jonathan Liu <net147@...il.com>, linux-pwm@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] pwm: sun4i: improve hardware read out

On Wed, May 31, 2017 at 3:35 PM, Alexandre Belloni
<alexandre.belloni@...e-electrons.com> wrote:
> On 31/05/2017 at 11:34:43 +0800, Chen-Yu Tsai wrote:
>> On Wed, May 31, 2017 at 3:32 AM, Alexandre Belloni
>> <alexandre.belloni@...e-electrons.com> wrote:
>> > +static void sun4i_pwm_get_state(struct pwm_chip *chip,
>> > +                               struct pwm_device *pwm,
>> > +                               struct pwm_state *state)
>> > +{
>> > +       struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip);
>> > +       u64 clk_rate, tmp;
>> > +       u32 val;
>> > +       unsigned int prescaler;
>> > +
>> > +       clk_rate = clk_get_rate(sun4i_pwm->clk);
>> > +
>> > +       val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
>> > +
>> > +       if ((val == PWM_PRESCAL_MASK) && sun4i_pwm->data->has_prescaler_bypass)
>> > +               prescaler = 1;
>> > +       else
>> > +               prescaler = prescaler_table[PWM_REG_PRESCAL(val, pwm->hwpwm)];
>> > +
>> > +       if (prescaler == 0)
>> > +               return;
>>
>> This looks like an invalid state. How does the PWM core handle it?
>> Or rather, how does the driver signal an invalid state?
>>
>
> It doesn't and it doesn't really matter, if the IP is in an invalid
> state, this bails out without modifying the know state so the core will
> behave as if there was no hardware read out and everything will be
> synchronized on the first ->apply() call.

Cool.

Thanks
ChenYu

>
>> Otherwise,
>>
>> Reviewed-by: Chen-Yu Tsai <wens@...e.org>
>>
>
> --
> Alexandre Belloni, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com