Re: [PATCH 03/10] pwm: sunxi: Yield some time to the pwm-block to become ready

[Chen-Yu Tsai <wens@csie.org>]

On Tue, Oct 27, 2015 at 5:32 AM, Olliver Schinagl
<o.schinagl@ultimaker.com> wrote:
> The pwm-block of some of the sunxi chips feature a 'ready' flag to
> indicate the software that it is ready for new commands.
>
> Right now, when we call pwm_config and set the period, we write the
> values to the registers, and turn off the clock to the IP. Because of
> this, the hardware does not have time to configure the hardware and set
> the 'ready' flag.
>
> By running the clock just before making new changes and before checking
> if the hardware is ready, the hardware has time to reconfigure itself
> and set the clear the flag appropriately.
>
> Signed-off-by: Olliver Schinagl <o.schinagl@ultimaker.com>
> ---
>  drivers/pwm/pwm-sun4i.c | 43 +++++++++++++++++++++++++------------------
>  1 file changed, 25 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> index 58ff424..4d84d9d 100644
> --- a/drivers/pwm/pwm-sun4i.c
> +++ b/drivers/pwm/pwm-sun4i.c
> @@ -104,6 +104,22 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>         u64 clk_rate, div = 0;
>         unsigned int prescaler = 0;
>         int err;
> +       int ret = 0;
> +
> +       /* Let the PWM hardware run before making any changes. We do this to
> +        * allow the hardware to have some time to clear the 'ready' flag.
> +        */
> +       err = clk_prepare_enable(sun4i_pwm->clk);
> +       if (err) {
> +               dev_err(chip->dev, "failed to enable PWM clock\n");
> +               return err;
> +       }
> +       spin_lock(&sun4i_pwm->ctrl_lock);
> +       val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +       clk_gate = val & BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +       val |= BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +       sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +       spin_unlock(&sun4i_pwm->ctrl_lock);
>
>         clk_rate = clk_get_rate(sun4i_pwm->clk);
>
> @@ -136,7 +152,9 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>
>                 if (div - 1 > PWM_PRD_MASK) {
>                         dev_err(chip->dev, "period exceeds the maximum value\n");
> -                       return -EINVAL;
> +                       ret = -EINVAL;
> +                       spin_lock(&sun4i_pwm->ctrl_lock);
> +                       goto out;
>                 }
>         }
>
> @@ -145,26 +163,14 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>         do_div(div, period_ns);
>         dty = div;
>
> -       err = clk_prepare_enable(sun4i_pwm->clk);
> -       if (err) {
> -               dev_err(chip->dev, "failed to enable PWM clock\n");
> -               return err;
> -       }
> -
>         spin_lock(&sun4i_pwm->ctrl_lock);
>         val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> -
>         if (sun4i_pwm->data->has_rdy && (val & PWM_RDY(pwm->hwpwm))) {

Instead of moving the code around to try to give the hardware some unspecified
time to run, could we use a tight busy loop with a timeout to read the register
and check if it's been cleared? I think that works better with cpufreq as well.

Thanks.

ChenYu

> -               spin_unlock(&sun4i_pwm->ctrl_lock);
> -               clk_disable_unprepare(sun4i_pwm->clk);
> -               return -EBUSY;
> -       }
> -
> -       clk_gate = val & BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> -       if (clk_gate) {
> -               val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> -               sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +               ret = -EBUSY;
> +               goto out;
>         }
> +       val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +       sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
>
>         val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
>         val &= ~BIT_CH(PWM_PRESCAL_MASK, pwm->hwpwm);
> @@ -174,6 +180,7 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>         val = (dty & PWM_DTY_MASK) | PWM_PRD(prd);
>         sun4i_pwm_writel(sun4i_pwm, val, PWM_CH_PRD(pwm->hwpwm));
>
> +out:
>         if (clk_gate) {
>                 val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
>                 val |= clk_gate;
> @@ -183,7 +190,7 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>         spin_unlock(&sun4i_pwm->ctrl_lock);
>         clk_disable_unprepare(sun4i_pwm->clk);
>
> -       return 0;
> +       return ret;
>  }
>
>  static int sun4i_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> --
> 2.6.1
>
>
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