linux-kernel - Re: [PATCH v8 5/5] pwm: core: Set enable state properly on failed call to enable

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Date:	Fri, 12 Jun 2015 12:22:29 -0700
From:	Jonathan Richardson <jonathar@...adcom.com>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Tim Kryger <tim.kryger@...il.com>,
	Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazau <anatol@...gle.com>,
	Arun Ramamurthy <arun.ramamurthy@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	<linux-kernel@...r.kernel.org>, <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v8 5/5] pwm: core: Set enable state properly on failed
 call to enable

On 15-06-12 02:49 AM, Thierry Reding wrote:
> On Tue, May 26, 2015 at 01:08:20PM -0700, 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 <jonathar@...adcom.com>
>> Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
>> Signed-off-by: Jonathan Richardson <jonathar@...adcom.com>
>> ---
>>  drivers/pwm/core.c |   16 +++++++++++++---
>>  1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>> index 224645f..18f5ac4 100644
>> --- a/drivers/pwm/core.c
>> +++ b/drivers/pwm/core.c
>> @@ -477,10 +477,20 @@ 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;
>> +
>> +	if (!pwm)
>> +		return -EINVAL;
>> +
>> +	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);
>> +			return err;
>> +		}
>> +	}
> 
> I think with this new pattern we're now actually going to need a lock to
> make sure pwm->flags doesn't change between the test_and_set_bit() and
> clear_bit() calls.
> 
> Thierry
> 

Ok. I'll add a lock per pwm_device and re-send the patch.

Jon
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