drm/i915/dsi: Lookup the i2c bus from ACPI NS only if CONFIG_ACPI=y (v2)

Perform the i2c bus/adapter lookup from ACPI Namespace only if ACPI is
enabled in the kernel config. If ACPI is not enabled or if the lookup
fails, we'll fallback to using the VBT for identifying the i2c bus.

v2: Add fixes tag (Jani)

Fixes: 8cbf89db ("drm/i915/dsi: Parse the I2C element from the VBT MIPI sequence block (v3)")
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Nabendu Maiti <nabendu.bikash.maiti@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Bob Paauwe <bob.j.paauwe@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200115012305.27395-1-vivek.kasireddy@intel.com

drivers/gpu/drm/i915/display/intel_dsi_vbt.c

@@ -384,6 +384,7 @@ static const u8 *mipi_exec_gpio(struct intel_dsi *intel_dsi, const u8 *data)
 	return data;
 }
 
+#ifdef CONFIG_ACPI
 static int i2c_adapter_lookup(struct acpi_resource *ares, void *data)
 {
 	struct i2c_adapter_lookup *lookup = data;
@@ -413,14 +414,41 @@ static int i2c_adapter_lookup(struct acpi_resource *ares, void *data)
 	return 1;
 }
 
-static const u8 *mipi_exec_i2c(struct intel_dsi *intel_dsi, const u8 *data)
+static void i2c_acpi_find_adapter(struct intel_dsi *intel_dsi,
+				  const u16 slave_addr)
 {
 	struct drm_device *drm_dev = intel_dsi->base.base.dev;
 	struct device *dev = &drm_dev->pdev->dev;
-	struct i2c_adapter *adapter;
 	struct acpi_device *acpi_dev;
 	struct list_head resource_list;
 	struct i2c_adapter_lookup lookup;
+
+	acpi_dev = ACPI_COMPANION(dev);
+	if (acpi_dev) {
+		memset(&lookup, 0, sizeof(lookup));
+		lookup.slave_addr = slave_addr;
+		lookup.intel_dsi = intel_dsi;
+		lookup.dev_handle = acpi_device_handle(acpi_dev);
+
+		INIT_LIST_HEAD(&resource_list);
+		acpi_dev_get_resources(acpi_dev, &resource_list,
+				       i2c_adapter_lookup,
+				       &lookup);
+		acpi_dev_free_resource_list(&resource_list);
+	}
+}
+#else
+static inline void i2c_acpi_find_adapter(struct intel_dsi *intel_dsi,
+					 const u16 slave_addr)
+{
+}
+#endif
+
+static const u8 *mipi_exec_i2c(struct intel_dsi *intel_dsi, const u8 *data)
+{
+	struct drm_device *drm_dev = intel_dsi->base.base.dev;
+	struct device *dev = &drm_dev->pdev->dev;
+	struct i2c_adapter *adapter;
 	struct i2c_msg msg;
 	int ret;
 	u8 vbt_i2c_bus_num = *(data + 2);
@@ -431,20 +459,7 @@ static const u8 *mipi_exec_i2c(struct intel_dsi *intel_dsi, const u8 *data)
 
 	if (intel_dsi->i2c_bus_num < 0) {
 		intel_dsi->i2c_bus_num = vbt_i2c_bus_num;
-
-		acpi_dev = ACPI_COMPANION(dev);
-		if (acpi_dev) {
-			memset(&lookup, 0, sizeof(lookup));
-			lookup.slave_addr = slave_addr;
-			lookup.intel_dsi = intel_dsi;
-			lookup.dev_handle = acpi_device_handle(acpi_dev);
-
-			INIT_LIST_HEAD(&resource_list);
-			acpi_dev_get_resources(acpi_dev, &resource_list,
-					       i2c_adapter_lookup,
-					       &lookup);
-			acpi_dev_free_resource_list(&resource_list);
-		}
+		i2c_acpi_find_adapter(intel_dsi, slave_addr);
 	}
 
 	adapter = i2c_get_adapter(intel_dsi->i2c_bus_num);