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

From: James Clark
Date: Thu Jan 05 2023 - 08:57:48 EST




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@xxxxxxxxxxx>
>> ---
>> 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