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SubjectRe: [PATCH v2 3/3] pwm: core: add consumer device link
Hello Fabrice,

On Mon, Feb 11, 2019 at 05:12:02PM +0100, Fabrice Gasnier wrote:
> Add a device link between the PWM consumer and the PWM provider. This
> enforces the PWM user to get suspended before the PWM provider. It
> allows proper synchronization of suspend/resume sequences: the PWM user
> is responsible for properly stopping PWM, before the provider gets
> suspended: see [1]. Add the device link in:
> - pwm_get()
> - devm_pwm_get()
> - devm_of_pwm_get()
> as it requires a reference to the device for the PWM consumer.
>
> [1] https://lkml.org/lkml/2019/2/5/770
>
> Suggested-by: Thierry Reding <thierry.reding@gmail.com>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
> ---
> drivers/pwm/core.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 1581f6a..2835e27 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -770,8 +770,13 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
> int err;
>
> /* look up via DT first */
> - if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
> - return of_pwm_get(dev->of_node, con_id);
> + if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node) {
> + pwm = of_pwm_get(dev->of_node, con_id);
> + if (!IS_ERR(pwm))
> + device_link_add(dev, pwm->chip->dev,
> + DL_FLAG_AUTOREMOVE_CONSUMER);
> + return pwm;
> + }
>
> /*
> * We look up the provider in the static table typically provided by
> @@ -851,6 +856,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
> pwm->args.period = chosen->period;
> pwm->args.polarity = chosen->polarity;
>
> + device_link_add(dev, pwm->chip->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> +
> return pwm;
> }
> EXPORT_SYMBOL_GPL(pwm_get);
> @@ -943,6 +950,8 @@ struct pwm_device *devm_of_pwm_get(struct device *dev, struct device_node *np,
> if (!IS_ERR(pwm)) {
> *ptr = pwm;
> devres_add(dev, ptr);
> + device_link_add(dev, pwm->chip->dev,
> + DL_FLAG_AUTOREMOVE_CONSUMER);

IMHO it's surprising that devm_of_pwm_get() does more than of_pwm_get()
+ devres stuff. I'd put device_link_add() into of_pwm_get().

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |

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