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

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

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.

Thanks
James