[PATCH v2 1/3] coresight: cti: Prevent negative values of enable count

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

Writing 0 to the enable control repeatedly results in a negative value
for enable_req_count. After this, writing 1 to the enable control
appears to not work until the count returns to positive.

Change it so that it's impossible for enable_req_count to be < 0.
Returning an error will also allow us to decide whether to call
runtime_pm_put() or not in the following commit.

Signed-off-by: James Clark <james.clark@arm.com>
---
 drivers/hwtracing/coresight/coresight-cti-core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-cti-core.c b/drivers/hwtracing/coresight/coresight-cti-core.c
index d2cf4f4848e1..838872f2484d 100644
--- a/drivers/hwtracing/coresight/coresight-cti-core.c
+++ b/drivers/hwtracing/coresight/coresight-cti-core.c
@@ -151,9 +151,16 @@ static int cti_disable_hw(struct cti_drvdata *drvdata)
 {
 	struct cti_config *config = &drvdata->config;
 	struct coresight_device *csdev = drvdata->csdev;
+	int ret = 0;
 
 	spin_lock(&drvdata->spinlock);
 
+	/* don't allow negative refcounts, return an error */
+	if (!atomic_read(&drvdata->config.enable_req_count)) {
+		ret = -EINVAL;
+		goto cti_not_disabled;
+	}
+
 	/* check refcount - disable on 0 */
 	if (atomic_dec_return(&drvdata->config.enable_req_count) > 0)
 		goto cti_not_disabled;
@@ -171,12 +178,12 @@ static int cti_disable_hw(struct cti_drvdata *drvdata)
 	coresight_disclaim_device_unlocked(csdev);
 	CS_LOCK(drvdata->base);
 	spin_unlock(&drvdata->spinlock);
-	return 0;
+	return ret;
 
 	/* not disabled this call */
 cti_not_disabled:
 	spin_unlock(&drvdata->spinlock);
-	return 0;
+	return ret;
 }
 
 void cti_write_single_reg(struct cti_drvdata *drvdata, int offset, u32 value)
-- 
2.25.1