* Re: [PATCH] pwm: twl: Reliably disable TWL6030 PWMs
2016-03-29 18:55 [PATCH] pwm: twl: Reliably disable TWL6030 PWMs Paul Kocialkowski
@ 2016-07-11 10:55 ` Thierry Reding
2016-07-12 13:18 ` Peter Ujfalusi
2016-09-05 5:14 ` Thierry Reding
2 siblings, 0 replies; 4+ messages in thread
From: Thierry Reding @ 2016-07-11 10:55 UTC (permalink / raw)
To: Paul Kocialkowski, Axel Lin, Peter Ujfalusi
Cc: linux-kernel, linux-pwm, Tony Lindgren, linux-omap
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On Tue, Mar 29, 2016 at 08:55:45PM +0200, Paul Kocialkowski wrote:
> The current TWL6030 code for the TWL PWM driver does not reliably disable the
> PWM output, as tested with LEDs. The previous commit to that driver introduced
> that regression.
>
> However, it does make sense to disable the PWM clock after resetting the PWM,
> but for some obscure reason, doing it all at once simply doesn't work.
>
> The TWL6030 datasheet mentions that PWMs have to be disabled in two distinct
> steps. However, clearing the clock enable bit in a second step (after issuing a
> reset first) does not work.
>
> The only approach that works is the one that was in place before the previous
> commit to the driver. It consists in enabling the PWM clock after issuing a
> reset. This is what TI kernel trees and production code seem to be using.
>
> However, adding an extra step to disable the PWM clock seems to work reliably,
> despite looking quite odd.
>
> Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
> ---
> drivers/pwm/pwm-twl.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
Axel, Peter,
can you guys comment on this?
Thierry
>
> diff --git a/drivers/pwm/pwm-twl.c b/drivers/pwm/pwm-twl.c
> index 04f7672..7a993b0 100644
> --- a/drivers/pwm/pwm-twl.c
> +++ b/drivers/pwm/pwm-twl.c
> @@ -269,6 +269,22 @@ static void twl6030_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> goto out;
> }
>
> + val |= TWL6030_PWM_TOGGLE(pwm->hwpwm, TWL6030_PWMXEN);
> +
> + ret = twl_i2c_write_u8(TWL6030_MODULE_ID1, val, TWL6030_TOGGLE3_REG);
> + if (ret < 0) {
> + dev_err(chip->dev, "%s: Failed to disable PWM\n", pwm->label);
> + goto out;
> + }
> +
> + val &= ~TWL6030_PWM_TOGGLE(pwm->hwpwm, TWL6030_PWMXEN);
> +
> + ret = twl_i2c_write_u8(TWL6030_MODULE_ID1, val, TWL6030_TOGGLE3_REG);
> + if (ret < 0) {
> + dev_err(chip->dev, "%s: Failed to disable PWM\n", pwm->label);
> + goto out;
> + }
> +
> twl->twl6030_toggle3 = val;
> out:
> mutex_unlock(&twl->mutex);
> --
> 2.7.4
>
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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] pwm: twl: Reliably disable TWL6030 PWMs
2016-03-29 18:55 [PATCH] pwm: twl: Reliably disable TWL6030 PWMs Paul Kocialkowski
2016-07-11 10:55 ` Thierry Reding
@ 2016-07-12 13:18 ` Peter Ujfalusi
2016-09-05 5:14 ` Thierry Reding
2 siblings, 0 replies; 4+ messages in thread
From: Peter Ujfalusi @ 2016-07-12 13:18 UTC (permalink / raw)
To: Paul Kocialkowski, linux-kernel, linux-pwm
Cc: Thierry Reding, Tony Lindgren, linux-omap
On 03/29/16 21:55, Paul Kocialkowski wrote:
> The current TWL6030 code for the TWL PWM driver does not reliably disable the
> PWM output, as tested with LEDs. The previous commit to that driver introduced
> that regression.
>
> However, it does make sense to disable the PWM clock after resetting the PWM,
> but for some obscure reason, doing it all at once simply doesn't work.
>
> The TWL6030 datasheet mentions that PWMs have to be disabled in two distinct
> steps. However, clearing the clock enable bit in a second step (after issuing a
> reset first) does not work.
>
> The only approach that works is the one that was in place before the previous
> commit to the driver. It consists in enabling the PWM clock after issuing a
> reset. This is what TI kernel trees and production code seem to be using.
>
> However, adding an extra step to disable the PWM clock seems to work reliably,
> despite looking quite odd.
Unfortunately I don't have board to test, but based on the documentation and
your explanation, this is the correct way.
Thank you for debugging and fixing it!
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>
> Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
> ---
> drivers/pwm/pwm-twl.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/drivers/pwm/pwm-twl.c b/drivers/pwm/pwm-twl.c
> index 04f7672..7a993b0 100644
> --- a/drivers/pwm/pwm-twl.c
> +++ b/drivers/pwm/pwm-twl.c
> @@ -269,6 +269,22 @@ static void twl6030_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> goto out;
> }
>
> + val |= TWL6030_PWM_TOGGLE(pwm->hwpwm, TWL6030_PWMXEN);
> +
> + ret = twl_i2c_write_u8(TWL6030_MODULE_ID1, val, TWL6030_TOGGLE3_REG);
> + if (ret < 0) {
> + dev_err(chip->dev, "%s: Failed to disable PWM\n", pwm->label);
> + goto out;
> + }
> +
> + val &= ~TWL6030_PWM_TOGGLE(pwm->hwpwm, TWL6030_PWMXEN);
> +
> + ret = twl_i2c_write_u8(TWL6030_MODULE_ID1, val, TWL6030_TOGGLE3_REG);
> + if (ret < 0) {
> + dev_err(chip->dev, "%s: Failed to disable PWM\n", pwm->label);
> + goto out;
> + }
> +
> twl->twl6030_toggle3 = val;
> out:
> mutex_unlock(&twl->mutex);
>
--
Péter
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] pwm: twl: Reliably disable TWL6030 PWMs
2016-03-29 18:55 [PATCH] pwm: twl: Reliably disable TWL6030 PWMs Paul Kocialkowski
2016-07-11 10:55 ` Thierry Reding
2016-07-12 13:18 ` Peter Ujfalusi
@ 2016-09-05 5:14 ` Thierry Reding
2 siblings, 0 replies; 4+ messages in thread
From: Thierry Reding @ 2016-09-05 5:14 UTC (permalink / raw)
To: Paul Kocialkowski; +Cc: linux-kernel, linux-pwm, Tony Lindgren, linux-omap
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On Tue, Mar 29, 2016 at 08:55:45PM +0200, Paul Kocialkowski wrote:
> The current TWL6030 code for the TWL PWM driver does not reliably disable the
> PWM output, as tested with LEDs. The previous commit to that driver introduced
> that regression.
>
> However, it does make sense to disable the PWM clock after resetting the PWM,
> but for some obscure reason, doing it all at once simply doesn't work.
>
> The TWL6030 datasheet mentions that PWMs have to be disabled in two distinct
> steps. However, clearing the clock enable bit in a second step (after issuing a
> reset first) does not work.
>
> The only approach that works is the one that was in place before the previous
> commit to the driver. It consists in enabling the PWM clock after issuing a
> reset. This is what TI kernel trees and production code seem to be using.
>
> However, adding an extra step to disable the PWM clock seems to work reliably,
> despite looking quite odd.
>
> Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
> ---
> drivers/pwm/pwm-twl.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
Applied, thanks.
Thierry
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^ permalink raw reply [flat|nested] 4+ messages in thread