sr_driver_init(): Improve checks.

Check the relevant arguments for != NULL before calling the actual
driver-specific function, so that the driver can safely assume those
arguments are non-NULL. This removes the need to duplicate these
checks in every driver.

Also, change one SR_ERR to the more correct SR_ERR_MALLOC, and assign
sr_ctx in the rigol-ds1xx2's hw_init() function, like all the other
drivers do.

hardware/asix-sigma/asix-sigma.c

@@ -426,6 +426,7 @@ static int hw_init(struct sr_context *sr_ctx)
 		sr_err("Driver context malloc failed.");
 		return SR_ERR_MALLOC;
 	}
+
 	drvc->sr_ctx = sr_ctx;
 	di->priv = drvc;
 

hardware/colead-slm/api.c

@@ -78,7 +78,7 @@ static int hw_init(struct sr_context *sr_ctx)
 
 	if (!(drvc = g_try_malloc0(sizeof(struct drv_context)))) {
 		sr_err("Driver context malloc failed.");
-		return SR_ERR;
+		return SR_ERR_MALLOC;
 	}
 
 	drvc->sr_ctx = sr_ctx;

hardware/demo/demo.c

@@ -154,6 +154,7 @@ static int hw_init(struct sr_context *sr_ctx)
 		sr_err("Driver context malloc failed.");
 		return SR_ERR_MALLOC;
 	}
+
 	drvc->sr_ctx = sr_ctx;
 	di->priv = drvc;
 

hardware/openbench-logic-sniffer/api.c

@@ -63,6 +63,7 @@ static int hw_init(struct sr_context *sr_ctx)
 		sr_err("Driver context malloc failed.");
 		return SR_ERR_MALLOC;
 	}
+
 	drvc->sr_ctx = sr_ctx;
 	di->priv = drvc;
 

hardware/rigol-ds1xx2/api.c

@@ -153,13 +153,13 @@ static int clear_instances(void)
 static int hw_init(struct sr_context *sr_ctx)
 {
 	struct drv_context *drvc;
-	(void)sr_ctx;
 
 	if (!(drvc = g_try_malloc0(sizeof(struct drv_context)))) {
 		sr_err("Driver context malloc failed.");
 		return SR_ERR_MALLOC;
 	}
 
+	drvc->sr_ctx = sr_ctx;
 	di->priv = drvc;
 
 	return SR_OK;

hardware/victor-dmm/api.c

@@ -80,6 +80,7 @@ static int hw_init(struct sr_context *sr_ctx)
 		sr_err("Driver context malloc failed.");
 		return SR_ERR_MALLOC;
 	}
+
 	drvc->sr_ctx = sr_ctx;
 	di->priv = drvc;
 

hardware/zeroplus-logic-cube/zeroplus.c

@@ -292,9 +292,10 @@ static int hw_init(struct sr_context *sr_ctx)
 	struct drv_context *drvc;
 
 	if (!(drvc = g_try_malloc0(sizeof(struct drv_context)))) {
-		sr_err("zeroplus: driver context malloc failed.");
+		sr_err("Driver context malloc failed.");
 		return SR_ERR_MALLOC;
 	}
+
 	drvc->sr_ctx = sr_ctx;
 	di->priv = drvc;
 

hwdriver.c

@@ -245,19 +245,38 @@ SR_API struct sr_dev_driver **sr_driver_list(void)
 /**
  * Initialize a hardware driver.
  *
- * @param ctx A libsigrok context object allocated by a previous call to
- * 		sr_init().
- * @param driver The driver to initialize.
+ * This usually involves memory allocations and variable initializations
+ * within the driver, but _not_ scanning for attached devices.
+ * The API call sr_driver_scan() is used for that.
  *
- * @return SR_OK if all went well, or an error code otherwise.
+ * @param ctx A libsigrok context object allocated by a previous call to
+ *            sr_init(). Must not be NULL.
+ * @param driver The driver to initialize. This must be a pointer to one of
+ *               the entries returned by sr_driver_list(). Must not be NULL.
+ *
+ * @return SR_OK upon success, SR_ERR_ARG upon invalid parameters,
+ *         SR_ERR_BUG upon internal errors, or another negative error code
+ *         upon other errors.
  */
 SR_API int sr_driver_init(struct sr_context *ctx, struct sr_dev_driver *driver)
 {
+	int ret;
 
-	if (driver->init)
-		return driver->init(ctx);
+	if (!ctx) {
+		sr_err("Invalid libsigrok context, can't initialize.");
+		return SR_ERR_ARG;
+	}
 
-	return SR_OK;
+	if (!driver) {
+		sr_err("Invalid driver, can't initialize.");
+		return SR_ERR_ARG;
+	}
+
+	sr_spew("Initializing driver '%s'.", driver->name);
+	if ((ret = driver->init(ctx)) < 0)
+		sr_err("Failed to initialize the driver: %d.", ret);
+
+	return ret;
 }
 
 /**