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

[James Clark <james.clark@arm.com>]

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.

James