[PATCH RFC/RFT 4/6] firmware: qcom: scm: Cleanup global '__scm' on probe failures

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

If SCM driver fails the probe, it should not leave global '__scm'
variable assigned, because external users of this driver will assume the
probe finished successfully.  For example TZMEM parts ('__scm->mempool')
are initialized later in the probe, but users of it (__scm_smc_call())
rely on the '__scm' variable.

This fixes theoretical NULL pointer exception, triggered via introducing
probe deferral in SCM driver with call trace:

  qcom_tzmem_alloc+0x70/0x1ac (P)
  qcom_tzmem_alloc+0x64/0x1ac (L)
  qcom_scm_assign_mem+0x78/0x194
  qcom_rmtfs_mem_probe+0x2d4/0x38c
  platform_probe+0x68/0xc8

Fixes: 40289e35ca52 ("firmware: qcom: scm: enable the TZ mem allocator")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

---

I am not really sure if authors wanted the cleanup at this point.

Also, I am not sure about commit introducing it (Fixes tag) thus not
Cc-ing stable.
---
 drivers/firmware/qcom/qcom_scm.c | 42 +++++++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 13 deletions(-)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index 93212c8f20ad65ecc44804b00f4b93e3eaaf8d95..c6d526d055003a17a8f59471f93160bbccfc1658 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -2036,13 +2036,17 @@ static int qcom_scm_probe(struct platform_device *pdev)
 
 	irq = platform_get_irq_optional(pdev, 0);
 	if (irq < 0) {
-		if (irq != -ENXIO)
-			return irq;
+		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)
-			return dev_err_probe(scm->dev, ret, "Failed to request qcom-scm irq\n");
+		if (ret < 0) {
+			dev_err_probe(scm->dev, ret, "Failed to request qcom-scm irq\n");
+			goto err;
+		}
 	}
 
 	__get_convention();
@@ -2061,14 +2065,18 @@ static int qcom_scm_probe(struct platform_device *pdev)
 		qcom_scm_disable_sdi();
 
 	ret = of_reserved_mem_device_init(__scm->dev);
-	if (ret && ret != -ENODEV)
-		return dev_err_probe(__scm->dev, ret,
-				     "Failed to setup the reserved memory region for TZ mem\n");
+	if (ret && ret != -ENODEV) {
+		dev_err_probe(__scm->dev, ret,
+			      "Failed to setup the reserved memory region for TZ mem\n");
+		goto err;
+	}
 
 	ret = qcom_tzmem_enable(__scm->dev);
-	if (ret)
-		return dev_err_probe(__scm->dev, ret,
-				     "Failed to enable the TrustZone memory allocator\n");
+	if (ret) {
+		dev_err_probe(__scm->dev, ret,
+			      "Failed to enable the TrustZone memory allocator\n");
+		goto err;
+	}
 
 	memset(&pool_config, 0, sizeof(pool_config));
 	pool_config.initial_size = 0;
@@ -2076,9 +2084,11 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	pool_config.max_size = SZ_256K;
 
 	__scm->mempool = devm_qcom_tzmem_pool_new(__scm->dev, &pool_config);
-	if (IS_ERR(__scm->mempool))
-		return dev_err_probe(__scm->dev, PTR_ERR(__scm->mempool),
-				     "Failed to create the SCM memory pool\n");
+	if (IS_ERR(__scm->mempool)) {
+		dev_err_probe(__scm->dev, PTR_ERR(__scm->mempool),
+			      "Failed to create the SCM memory pool\n");
+		goto err;
+	}
 
 	/*
 	 * Initialize the QSEECOM interface.
@@ -2094,6 +2104,12 @@ 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, 0);
+
+	return ret;
 }
 
 static void qcom_scm_shutdown(struct platform_device *pdev)

-- 
2.43.0