On 15-08-17 07:31 AM, Thierry Reding wrote:
> On Mon, Jun 15, 2015 at 04:22:27PM -0700, Jonathan Richardson wrote:
>> On 15-06-15 02:21 PM, Jonathan Richardson wrote:
>>> The pwm_enable function didn't clear the enabled bit if a call to a
>>> clients enable function returned an error. The result was that the state
>>> of the pwm core was wrong. Clearing the bit when enable returns an error
>>> ensures the state is properly set.
>>>
>>> Tested-by: Jonathan Richardson <jonat...@broadcom.com>
>>> Reviewed-by: Dmitry Torokhov <dmitry.torok...@gmail.com>
>>> Signed-off-by: Jonathan Richardson <jonat...@broadcom.com>
>>> ---
>>> drivers/pwm/core.c | 19 ++++++++++++++++---
>>> include/linux/pwm.h | 2 ++
>>> 2 files changed, 18 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>>> index 76b0386..c255267 100644
>>> --- a/drivers/pwm/core.c
>>> +++ b/drivers/pwm/core.c
>>> @@ -263,6 +263,7 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
>>> pwm->pwm = chip->base + i;
>>> pwm->hwpwm = i;
>>> pwm->polarity = polarity;
>>> + mutex_init(&pwm->lock);
>>>
>>> radix_tree_insert(&pwm_tree, pwm->pwm, pwm);
>>> }
>>> @@ -474,10 +475,22 @@ EXPORT_SYMBOL_GPL(pwm_set_polarity);
>>> */
>>> int pwm_enable(struct pwm_device *pwm)
>>> {
>>> - if (pwm && !test_and_set_bit(PWMF_ENABLED, &pwm->flags))
>>> - return pwm->chip->ops->enable(pwm->chip, pwm);
>>> + int err = 0;
>>>
>>> - return pwm ? 0 : -EINVAL;
>>> + if (!pwm)
>>> + return -EINVAL;
>>> +
>>> + mutex_lock(&pwm->lock);
>>> +
>>> + if (!test_and_set_bit(PWMF_ENABLED, &pwm->flags)) {
>>> + err = pwm->chip->ops->enable(pwm->chip, pwm);
>>> + if (err)
>>> + clear_bit(PWMF_ENABLED, &pwm->flags);
>>> + }
>>> +
>>> + mutex_unlock(&pwm->lock);
>>> +
>>> + return err;
>>> }
>>> EXPORT_SYMBOL_GPL(pwm_enable);
>>
>> I meant to add the mutex check in disable also, but what about when
>> PWMF_ENABLED is checked in pwm_set_polarity() and pwm_dbg_show()?
>
> I think for debugfs we're fine since there's no potential to race there.
> It'll simply show the state of the PWM at the point where it was queried
> even though that may change immediately after. I suppose we could keep
> the lock across the body of the loop just to make sure debugfs will show
> a consistent view of the PWM.
>
> For pwm_disable() I don't think we need the lock, since the test_and_
> clear_bit() is atomic and ->disable() cannot fail.
>
> As for pwm_set_polarity(), I think it would need to be something like
> the below:
>
> ---- >8 ----
>
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 3f9df3ea3350..8488c7a19bf6 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -473,16 +473,22 @@ int pwm_set_polarity(struct pwm_device *pwm, enum
> pwm_polarity polarity)
> if (!pwm->chip->ops->set_polarity)
> return -ENOSYS;
>
> - if (pwm_is_enabled(pwm))
> - return -EBUSY;
> + mutex_lock(&pwm->lock);
> +
> + if (pwm_is_enabled(pwm)) {
> + err = -EBUSY;
> + goto unlock;
> + }
>
> err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
> if (err)
> - return err;
> + goto unlock;
>
> pwm->polarity = polarity;
>
> - return 0;
> +unlock:
> + mutex_unlock(&pwm->lock);
> + return err;
> }
> EXPORT_SYMBOL_GPL(pwm_set_polarity);
>
>
Thierry,
Sounds good to me. I'll send a patch out for this hopefully today. I
don't see a need to complicate debugfs with obscure functionality so the
patch will just add polarity as you have shown it here and the enable
routine as the previous patchset.
Jon
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