firmware: qcom: scm: request the waitqueue irq *after* initializing SCM

There's a subtle race in the SCM driver: we assign the __scm pointer
before requesting the waitqueue interrupt. Assigning __scm marks the SCM
API as ready to accept calls. It's possible that a user makes a call
right after we set __scm and the firmware raises an interrupt before the
driver's ready to service it. Move the __scm assignment after we request
the interrupt.

This has the added benefit of allowing us to drop the goto label.

Reviewed-by: Konrad Dybcio <[email protected]>
Signed-off-by: Bartosz Golaszewski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Bjorn Andersson <[email protected]>

Author: Bartosz Golaszewski

drivers/firmware/qcom/qcom_scm.c

@@ -2276,29 +2276,27 @@ static int qcom_scm_probe(struct platform_device *pdev)
 		return dev_err_probe(scm->dev, PTR_ERR(scm->mempool),
 				     "Failed to create the SCM memory pool\n");
 
+	irq = platform_get_irq_optional(pdev, 0);
+	if (irq < 0) {
+		if (irq != -ENXIO)
+			return irq;
+	} else {
+		ret = devm_request_threaded_irq(scm->dev, irq, NULL, qcom_scm_irq_handler,
+						IRQF_ONESHOT, "qcom-scm", scm);
+		if (ret < 0)
+			return dev_err_probe(scm->dev, ret,
+					     "Failed to request qcom-scm irq\n");
+	}
+
 	/*
 	 * Paired with smp_load_acquire() in qcom_scm_is_available().
 	 *
 	 * This marks the SCM API as ready to accept user calls and can only
-	 * be called after the TrustZone memory pool is initialized.
+	 * be called after the TrustZone memory pool is initialized and the
+	 * waitqueue interrupt requested.
 	 */
 	smp_store_release(&__scm, scm);
 
-	irq = platform_get_irq_optional(pdev, 0);
-	if (irq < 0) {
-		if (irq != -ENXIO) {
-			ret = irq;
-			goto err;
-		}
-	} else {
-		ret = devm_request_threaded_irq(__scm->dev, irq, NULL, qcom_scm_irq_handler,
-						IRQF_ONESHOT, "qcom-scm", __scm);
-		if (ret < 0) {
-			dev_err_probe(scm->dev, ret, "Failed to request qcom-scm irq\n");
-			goto err;
-		}
-	}
-
 	__get_convention();
 
 	/*
@@ -2328,12 +2326,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	WARN(ret < 0, "failed to initialize qseecom: %d\n", ret);
 
 	return 0;
-
-err:
-	/* Paired with smp_load_acquire() in qcom_scm_is_available(). */
-	smp_store_release(&__scm, NULL);
-
-	return ret;
 }
 
 static void qcom_scm_shutdown(struct platform_device *pdev)