On 14/03/2014 15:19, Alexandre Belloni :
> When atmel_pwm_config() calculates and then sets the prescaler, it is
> overwriting the channel's CMR register so we are losing the CPOL
> configuration.
>
> As atmel_pwm_config() is always called before enabling a channel, inverting
> the
> polarity doesn't work.
>
> Fix that by reading CMR first and only overwriting the prescaler bits.
>
> Signed-off-by: Alexandre Belloni <alexandre.bell...@free-electrons.com>
Indeed:
Acked-by: Nicolas Ferre <nicolas.fe...@atmel.com>
> ---
> drivers/pwm/pwm-atmel.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index bf4144a14661..2d69e9c431dd 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -32,6 +32,7 @@
> /* Bit field in CMR */
> #define PWM_CMR_CPOL (1 << 9)
> #define PWM_CMR_UPD_CDTY (1 << 10)
> +#define PWM_CMR_CPRE_MSK 0xF
>
> /* The following registers for PWM v1 */
> #define PWMV1_CDTY 0x04
> @@ -104,6 +105,7 @@ static int atmel_pwm_config(struct pwm_chip *chip, struct
> pwm_device *pwm,
> unsigned long clk_rate, prd, dty;
> unsigned long long div;
> unsigned int pres = 0;
> + u32 val;
> int ret;
>
> if (test_bit(PWMF_ENABLED, &pwm->flags) && (period_ns != pwm->period)) {
> @@ -139,7 +141,10 @@ static int atmel_pwm_config(struct pwm_chip *chip,
> struct pwm_device *pwm,
> return ret;
> }
>
> - atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, pres);
> + /* 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);
> + atmel_pwm_ch_writel(atmel_pwm, pwm->hwpwm, PWM_CMR, val);
> atmel_pwm->config(chip, pwm, dty, prd);
>
> clk_disable(atmel_pwm->clk);
>
--
Nicolas Ferre
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