[PATCH v2 4/4] firmware: qcom: scm: Fix __scm and waitq completion variable initialization

[Mukesh Ojha <quic_mojha@quicinc.com>]

It is possible qcom_scm_is_available() gives wrong indication that
if __scm is initialized while __scm->dev is not and similar issue
is also possible with __scm->waitq_comp.

Fix this appropriately by the use of release barrier and read barrier
that will make sure if __scm is initialized so, is all of its field
variable.

Fixes: d0f6fa7ba2d6 ("firmware: qcom: scm: Convert SCM to platform driver")
Fixes: 6bf325992236 ("firmware: qcom: scm: Add wait-queue handling logic")
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
---
Changes in v2:
 - Added barrier instruction to make the stores available only
   after __scm initialization.
 - Moved __scm->waitq_comp initialized slight up in program order.
 - Added Fixes tag.

 drivers/firmware/qcom/qcom_scm.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index e238ebe21099..f014a934a603 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1737,7 +1737,7 @@ static int qcom_scm_qseecom_init(struct qcom_scm *scm)
  */
 bool qcom_scm_is_available(void)
 {
-	return !!__scm;
+	return !!READ_ONCE(__scm);
 }
 EXPORT_SYMBOL_GPL(qcom_scm_is_available);
 
@@ -1818,10 +1818,12 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (!scm)
 		return -ENOMEM;
 
+	scm->dev = &pdev->dev;
 	ret = qcom_scm_find_dload_address(&pdev->dev, &scm->dload_mode_addr);
 	if (ret < 0)
 		return ret;
 
+	init_completion(&scm->waitq_comp);
 	mutex_init(&scm->scm_bw_lock);
 
 	scm->path = devm_of_icc_get(&pdev->dev, NULL);
@@ -1853,10 +1855,8 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	__scm = scm;
-	__scm->dev = &pdev->dev;
-
-	init_completion(&__scm->waitq_comp);
+	/* Let all above stores be available after this */
+	smp_store_release(&__scm, scm);
 
 	irq = platform_get_irq_optional(pdev, 0);
 	if (irq < 0) {
-- 
2.7.4