Coresight: Set correct cs_mode for dummy source to fix disable issue

The coresight_disable_source_sysfs function should verify the
mode of the coresight device before disabling the source.
However, the mode for the dummy source device is always set to
CS_MODE_DISABLED, resulting in the check consistently failing.
As a result, dummy source cannot be properly disabled.

Configure CS_MODE_SYSFS/CS_MODE_PERF during the enablement.
Configure CS_MODE_DISABLED during the disablement.

Fixes: 9d3ba0b6 ("Coresight: Add coresight dummy driver")
Signed-off-by: Jie Gan <quic_jiegan@quicinc.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20240812042844.2890115-1-quic_jiegan@quicinc.com

drivers/hwtracing/coresight/coresight-dummy.c

@@ -23,6 +23,9 @@ DEFINE_CORESIGHT_DEVLIST(sink_devs, "dummy_sink");
 static int dummy_source_enable(struct coresight_device *csdev,
 			       struct perf_event *event, enum cs_mode mode)
 {
+	if (!coresight_take_mode(csdev, mode))
+		return -EBUSY;
+
 	dev_dbg(csdev->dev.parent, "Dummy source enabled\n");
 
 	return 0;
@@ -31,6 +34,7 @@ static int dummy_source_enable(struct coresight_device *csdev,
 static void dummy_source_disable(struct coresight_device *csdev,
 				 struct perf_event *event)
 {
+	coresight_set_mode(csdev, CS_MODE_DISABLED);
 	dev_dbg(csdev->dev.parent, "Dummy source disabled\n");
 }