[2/2] coresight: Fix reference count for software sources
Suzuki K Poulose
Suzuki.Poulose at arm.com
Tue Mar 14 11:06:30 PDT 2017
On 14/03/17 17:40, Mathieu Poirier wrote:
> On 14 March 2017 at 11:32, Mathieu Poirier <mathieu.poirier at linaro.org> wrote:
>> From: "Suzuki K. Poulose" <Suzuki.Poulose at arm.com>
>>
>> For software sources (i.e STM), there could be multiple agents
>> generating the trace data, unlike the ETMs. So we need to
>> properly do the accounting for the active number of users
>> to disable the device when the last user goes away. Right
>> now, the reference counting is broken for sources as we skip
>> the actions when we detect that the source is enabled.
>>
>> This patch fixes the problem by adding the refcounting for
>> software sources, even when they are enabled.
>>
>> Cc: Mathieu Poirier <mathieu.poirier at linaro.org>
>> Reported-by: Robert Walker <robert.walker at arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
>> ---
>> drivers/hwtracing/coresight/coresight.c | 13 +++++++++++--
>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
>> index 34cd1ed..2da9e39 100644
>> --- a/drivers/hwtracing/coresight/coresight.c
>> +++ b/drivers/hwtracing/coresight/coresight.c
>> @@ -552,6 +552,7 @@ int coresight_enable(struct coresight_device *csdev)
>> int cpu, ret = 0;
>> struct coresight_device *sink;
>> struct list_head *path;
>> + enum coresight_dev_subtype_source subtype = csdev->subtype.source_subtype;
>
> Checkpatch.pl complains about a line over 80 characters.
>
>>
>> mutex_lock(&coresight_mutex);
>>
>> @@ -559,8 +560,16 @@ int coresight_enable(struct coresight_device *csdev)
>> if (ret)
>> goto out;
>>
>> - if (csdev->enable)
>> + if (csdev->enable) {
>> + /*
>> + * There could be multiple applications driving the software
>> + * source. So keep the refcount for each such user when the
>> + * source is already enabled.
>> + */
>> + if (subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
>> + atomic_inc(csdev->refcnt);
>> goto out;
>> + }
>>
Btw, should we allow the user to turn on the STM from sysfs (echo 1 > $STM/enable_source) ?
All STM users should set their policy via ioctls and that in turn turns the device on. So
it doesn't make sense for enable_source to really enable the hardware unless someone really
opens it.
Chunyan, Mathieu,
thoughts ?
Suzuki
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