drm/nouveau/bl: Assign different names to interfaces

Currently, every backlight interface created by Nouveau uses the same name,
nv_backlight. This leads to a sysfs warning as it tries to create an already
existing folder. This patch adds a incremented number to the name, but keeps
the initial name as nv_backlight, to avoid possibly breaking userspace; the
second interface will be named nv_backlight1, and so on.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86539

v2:
* Switch to using ida for generating unique IDs, as suggested by Ilia Mirkin;
* Allocate backlight name on the stack, as suggested by Ilia Mirkin;
* Move `nouveau_get_backlight_name()` to avoid forward declaration, as
  suggested by Ilia Mirkin;
* Fix reference to bug report formatting, as reported by Nick Tenney.

v3:
* Define a macro for the size of the backlight name, to avoid defining
  it multiple times;
* Use snprintf in place of sprintf.

v4:
* Do not create similarly named interfaces when reaching the maximum
  amount of unique names, but fail instead, as pointed out by Lukas Wunner
Signed-off-by: Pierre Moreau <pierre.morrow@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_backlight.c

@@ -31,11 +31,35 @@
  */
 
 #include <linux/backlight.h>
+#include <linux/idr.h>
 
 #include "nouveau_drv.h"
 #include "nouveau_reg.h"
 #include "nouveau_encoder.h"
 
+static struct ida bl_ida;
+#define BL_NAME_SIZE 15 // 12 for name + 2 for digits + 1 for '\0'
+
+struct backlight_connector {
+	struct list_head head;
+	int id;
+};
+
+static bool
+nouveau_get_backlight_name(char backlight_name[BL_NAME_SIZE], struct backlight_connector
+		*connector)
+{
+	const int nb = ida_simple_get(&bl_ida, 0, 0, GFP_KERNEL);
+	if (nb < 0 || nb >= 100)
+		return false;
+	if (nb > 0)
+		snprintf(backlight_name, BL_NAME_SIZE, "nv_backlight%d", nb);
+	else
+		snprintf(backlight_name, BL_NAME_SIZE, "nv_backlight");
+	connector->id = nb;
+	return true;
+}
+
 static int
 nv40_get_intensity(struct backlight_device *bd)
 {
@@ -74,6 +98,8 @@ nv40_backlight_init(struct drm_connector *connector)
 	struct nvif_object *device = &drm->device.object;
 	struct backlight_properties props;
 	struct backlight_device *bd;
+	struct backlight_connector bl_connector;
+	char backlight_name[BL_NAME_SIZE];
 
 	if (!(nvif_rd32(device, NV40_PMC_BACKLIGHT) & NV40_PMC_BACKLIGHT_MASK))
 		return 0;
@@ -81,10 +107,19 @@ nv40_backlight_init(struct drm_connector *connector)
 	memset(&props, 0, sizeof(struct backlight_properties));
 	props.type = BACKLIGHT_RAW;
 	props.max_brightness = 31;
-	bd = backlight_device_register("nv_backlight", connector->kdev, drm,
+	if (!nouveau_get_backlight_name(backlight_name, &bl_connector)) {
+		NV_ERROR(drm, "Failed to retrieve a unique name for the backlight interface\n");
+		return 0;
+	}
+	bd = backlight_device_register(backlight_name , connector->kdev, drm,
 				       &nv40_bl_ops, &props);
-	if (IS_ERR(bd))
+
+	if (IS_ERR(bd)) {
+		if (bl_connector.id > 0)
+			ida_simple_remove(&bl_ida, bl_connector.id);
 		return PTR_ERR(bd);
+	}
+	list_add(&bl_connector.head, &drm->bl_connectors);
 	drm->backlight = bd;
 	bd->props.brightness = nv40_get_intensity(bd);
 	backlight_update_status(bd);
@@ -182,6 +217,8 @@ nv50_backlight_init(struct drm_connector *connector)
 	struct backlight_properties props;
 	struct backlight_device *bd;
 	const struct backlight_ops *ops;
+	struct backlight_connector bl_connector;
+	char backlight_name[BL_NAME_SIZE];
 
 	nv_encoder = find_encoder(connector, DCB_OUTPUT_LVDS);
 	if (!nv_encoder) {
@@ -203,11 +240,20 @@ nv50_backlight_init(struct drm_connector *connector)
 	memset(&props, 0, sizeof(struct backlight_properties));
 	props.type = BACKLIGHT_RAW;
 	props.max_brightness = 100;
-	bd = backlight_device_register("nv_backlight", connector->kdev,
+	if (!nouveau_get_backlight_name(backlight_name, &bl_connector)) {
+		NV_ERROR(drm, "Failed to retrieve a unique name for the backlight interface\n");
+		return 0;
+	}
+	bd = backlight_device_register(backlight_name , connector->kdev,
 				       nv_encoder, ops, &props);
-	if (IS_ERR(bd))
+
+	if (IS_ERR(bd)) {
+		if (bl_connector.id > 0)
+			ida_simple_remove(&bl_ida, bl_connector.id);
 		return PTR_ERR(bd);
+	}
 
+	list_add(&bl_connector.head, &drm->bl_connectors);
 	drm->backlight = bd;
 	bd->props.brightness = bd->ops->get_brightness(bd);
 	backlight_update_status(bd);
@@ -221,6 +267,8 @@ nouveau_backlight_init(struct drm_device *dev)
 	struct nvif_device *device = &drm->device;
 	struct drm_connector *connector;
 
+	INIT_LIST_HEAD(&drm->bl_connectors);
+
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
 		if (connector->connector_type != DRM_MODE_CONNECTOR_LVDS &&
 		    connector->connector_type != DRM_MODE_CONNECTOR_eDP)
@@ -247,9 +295,27 @@ void
 nouveau_backlight_exit(struct drm_device *dev)
 {
 	struct nouveau_drm *drm = nouveau_drm(dev);
+	struct backlight_connector *connector;
+
+	list_for_each_entry(connector, &drm->bl_connectors, head) {
+		if (connector->id >= 0)
+			ida_simple_remove(&bl_ida, connector->id);
+	}
 
 	if (drm->backlight) {
 		backlight_device_unregister(drm->backlight);
 		drm->backlight = NULL;
 	}
 }
+
+void
+nouveau_backlight_ctor(void)
+{
+	ida_init(&bl_ida);
+}
+
+void
+nouveau_backlight_dtor(void)
+{
+	ida_destroy(&bl_ida);
+}

drivers/gpu/drm/nouveau/nouveau_display.h

@@ -91,6 +91,8 @@ int nouveau_crtc_set_config(struct drm_mode_set *set);
 #ifdef CONFIG_DRM_NOUVEAU_BACKLIGHT
 extern int nouveau_backlight_init(struct drm_device *);
 extern void nouveau_backlight_exit(struct drm_device *);
+extern void nouveau_backlight_ctor(void);
+extern void nouveau_backlight_dtor(void);
 #else
 static inline int
 nouveau_backlight_init(struct drm_device *dev)
@@ -101,6 +103,14 @@ nouveau_backlight_init(struct drm_device *dev)
 static inline void
 nouveau_backlight_exit(struct drm_device *dev) {
 }
+
+static inline void
+nouveau_backlight_ctor(void) {
+}
+
+static inline void
+nouveau_backlight_dtor(void) {
+}
 #endif
 
 struct drm_framebuffer *

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -1122,6 +1122,7 @@ nouveau_drm_init(void)
 #endif
 
 	nouveau_register_dsm_handler();
+	nouveau_backlight_ctor();
 	return drm_pci_init(&driver_pci, &nouveau_drm_pci_driver);
 }
 
@@ -1132,6 +1133,7 @@ nouveau_drm_exit(void)
 		return;
 
 	drm_pci_exit(&driver_pci, &nouveau_drm_pci_driver);
+	nouveau_backlight_dtor();
 	nouveau_unregister_dsm_handler();
 
 #ifdef CONFIG_NOUVEAU_PLATFORM_DRIVER

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -163,6 +163,7 @@ struct nouveau_drm {
 	struct nvbios vbios;
 	struct nouveau_display *display;
 	struct backlight_device *backlight;
+	struct list_head bl_connectors;
 	struct work_struct hpd_work;
 #ifdef CONFIG_ACPI
 	struct notifier_block acpi_nb;