Re: [PATCH] coresight: cti: Add PM runtime call in enable_store

[Jinlong Mao <quic_jinlmao@quicinc.com>]

On 1/5/2023 9:55 PM, James Clark wrote:
>
> On 04/01/2023 13:11, James Clark wrote:
>>
>> On 24/12/2022 14:17, Mao Jinlong wrote:
>>> In commit 6746eae4bbad ("coresight: cti: Fix hang in cti_disable_hw()")
>>> PM runtime calls are removed from cti_enable_hw/cti_disable_hw. When
>>> enabling CTI by writing enable sysfs node, clock for accessing CTI
>>> register won't be enabled. Device will crash due to register access
>>> issue. Add PM runtime call in enable_store to fix this issue.
>>>
>>> Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
>>> ---
>>>   drivers/hwtracing/coresight/coresight-cti-sysfs.c | 11 +++++++++--
>>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-cti-sysfs.c b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
>>> index 6d59c815ecf5..b1ed424ae043 100644
>>> --- a/drivers/hwtracing/coresight/coresight-cti-sysfs.c
>>> +++ b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
>>> @@ -108,10 +108,17 @@ static ssize_t enable_store(struct device *dev,
>>>   	if (ret)
>>>   		return ret;
>>>   
>>> -	if (val)
>>> +	if (val) {
>>> +		ret = pm_runtime_resume_and_get(dev->parent);
>>> +		if (ret)
>>> +			return ret;
>>>   		ret = cti_enable(drvdata->csdev);
>>> -	else
>>> +		if (ret)
>>> +			pm_runtime_put(dev->parent);
>>> +	} else {
>>>   		ret = cti_disable(drvdata->csdev);
>>> +		pm_runtime_put(dev->parent);
>> Hi Jinlong,
>>
>> This new pm_runtime_put() causes this when writing 0 to enable:
>>
>>    [  483.253814] coresight-cti 23020000.cti: Runtime PM usage count
>> underflow!
>>
>> Maybe we can modify cti_disable_hw() to return a value to indicate that
>> the disable actually happened, and only then call pm_runtime_put().
>>
>> I suppose you could also check in the store function if it was already
>> enabled first, but then I don't know what kind of locking that would
>> need? cti_disable_hw() already seems to have a couple of locks, so maybe
>> the return value solution is easiest.
>>
> We've also just seen another issue where multiple calls to
> cti_disable_hw() can cause enable_req_count to go negative. I'm going to
> work on a few fixes (including yours) to make sure that it's complete
> and post it shortly.
Ok, Thank you, James.
>
> James