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>

4 files changed, 83 insertions, 4 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index 5e2c5685b4dd..a34cd35d4965 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/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);
+}
diff --git a/drivers/gpu/drm/nouveau/nouveau_display.h b/drivers/gpu/drm/nouveau/nouveau_display.h
index 330fe0fc5c11..4a75df06c139 100644
--- a/drivers/gpu/drm/nouveau/nouveau_display.h
+++ b/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 *
diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 064a925ed69a..59348fc41c77 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/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
diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
index 9730c0ef6c6a..8d5ed5bfdacb 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drv.h
+++ b/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;