firmware: qcom: scm: Fix __scm and waitq completion variable initialization

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: d0f6fa7 ("firmware: qcom: scm: Convert SCM to platform driver")
Fixes: 6bf3259 ("firmware: qcom: scm: Add wait-queue handling logic")
Signed-off-by: Mukesh Ojha <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Bjorn Andersson <[email protected]>

Author: Mukesh Ojha

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) {