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

Chen-Yu Tsai
2015-11-06T16:34:56Z

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
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel