Re: [PATCH v2 1/2] drivers: pwm: pwm-atmel: switch to atomic PWM

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi Claudiu,

On Thu, 2 Mar 2017 17:28:44 +0200
Claudiu Beznea <claudiu.beznea@microchip.com> wrote:

> The currently Atmel PWM controllers supported by this driver
> could change period or duty factor without channel disable,
> for regular channels (sama5d3 support this by using period
> or duty factor update registers, sam9rl support this by
> writing channel update register and select the corresponding
> update: period or duty factor). The chip doesn't support run
> time changings of signal polarity. To take advantage of
> atomic PWM framework and let controller works without glitches,
> in this patch only the duty factor could be changed without
> disabling PWM channel. For period and signal polarity the
> atomic PWM is simulated by disabling + enabling the right PWM channel.
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
> 
> ---
>  drivers/pwm/pwm-atmel.c | 271 ++++++++++++++++++++++++------------------------
>  1 file changed, 138 insertions(+), 133 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index 67a7023..3db82c3 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -58,17 +58,30 @@
>  #define PWM_MAX_PRD		0xFFFF
>  #define PRD_MAX_PRES		10
>  
> +struct atmel_pwm_reg_data {
> +	u8 period;
> +	u8 period_upd;
> +	u8 duty;
> +	u8 duty_upd;
> +};
> +
> +struct atmel_pwm_data {
> +	void (*update_cdty)(struct pwm_chip *chip, struct pwm_device *pwm,
> +			    unsigned long cdty);
> +	void (*set_cprd_cdty)(struct pwm_chip *chip, struct pwm_device *pwm,
> +			      unsigned long cprd, unsigned long cdty);
> +	const struct atmel_pwm_reg_data regs;

If you go for this per-IP reg layout definition approach, you don't need
the ->update_cdty()/->set_cprd_cdty() hooks anymore.

> +};
> +

[...]

> +static int atmel_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			   struct pwm_state *state)
> +{
> +	struct atmel_pwm_chip *atmel_pwm = to_atmel_pwm_chip(chip);
> +	struct pwm_state cstate;
> +	unsigned long cprd, cdty;
> +	u32 pres, val;
> +	bool pwm_reset = false;
> +	int ret;
> +
> +	pwm_get_state(pwm, &cstate);
> +
> +	if (cstate.enabled &&
> +	    (cstate.polarity != state->polarity ||
> +	     cstate.period != state->period))
> +		pwm_reset = true;

You can move that in the 'if (state->enabled)' block, but I'm not even
sure this is really needed (see below).

> +
> +	if (state->enabled) {
> +		if (cstate.enabled && !pwm_reset) {

		if (cstate.enabled &&
		    (cstate.polarity != state->polarity ||
		     cstate.period != state->period)) {

> +			cprd = atmel_pwm_ch_readl(atmel_pwm, pwm->hwpwm,
> +						  atmel_pwm->data->regs.period);
> +			atmel_pwm_calculate_cdty(state, cprd, &cdty);
> +			atmel_pwm->data->update_cdty(chip, pwm, cdty);
> +			return 0;
> +		}
> +
> +		ret = atmel_pwm_calculate_cprd_and_pres(chip, state, &cprd,
> +							&pres);
> +		if (ret) {
> +			dev_err(chip->dev,
> +				"failed to calculate cprd and prescaler\n");
> +			return ret;
> +		}
> +
> +		atmel_pwm_calculate_cdty(state, cprd, &cdty);
> +
> +		if (pwm_reset) {

		if (cstate.enabled) {

> +			atmel_pwm_disable(chip, pwm, false);
> +		} else {
> +			ret = clk_enable(atmel_pwm->clk);
> +			if (ret) {
> +				dev_err(chip->dev, "failed to enable clock\n");
> +				return ret;
> +			}
> +		}
> +
> +		/* It is necessary to preserve CPOL, inside CMR */
> +		val = atmel_pwm_ch_readl(atmel_pwm, pwm->hwpwm, PWM_CMR);
> +		val = (val & ~PWM_CMR_CPRE_MSK) | (pres & PWM_CMR_CPRE_MSK);
> +		if (state->polarity == PWM_POLARITY_NORMAL)
> +			val &= ~PWM_CMR_CPOL;
> +		else
> +			val |= PWM_CMR_CPOL;
> +		atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, val);
> +		atmel_pwm->data->set_cprd_cdty(chip, pwm, cprd, cdty);
> +		mutex_lock(&atmel_pwm->isr_lock);
> +		atmel_pwm->updated_pwms |= atmel_pwm_readl(atmel_pwm, PWM_ISR);
> +		atmel_pwm->updated_pwms &= ~(1 << pwm->hwpwm);
> +		mutex_unlock(&atmel_pwm->isr_lock);
> +		atmel_pwm_writel(atmel_pwm, PWM_ENA, 1 << pwm->hwpwm);
> +	} else if (cstate.enabled) {
> +		atmel_pwm_disable(chip, pwm, true);
> +	}
> +
> +	return 0;
>  }