[PATCH 1/2] nouveau/bl: Assign different names to interfaces

[Pierre Moreau <pierre.morrow@xxxxxxx>]

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.

Fixes: fdo#86539
Signed-off-by: Pierre Moreau <pierre.morrow@xxxxxxx>
---
 drm/nouveau/nouveau_backlight.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drm/nouveau/nouveau_backlight.c b/drm/nouveau/nouveau_backlight.c
index 89eb460..914e2cb 100644
--- a/drm/nouveau/nouveau_backlight.c
+++ b/drm/nouveau/nouveau_backlight.c
@@ -36,6 +36,10 @@
 #include "nouveau_reg.h"
 #include "nouveau_encoder.h"
 
+static atomic_t bl_interfaces_nb = { 0 };
+
+static char* nouveau_get_backlight_name(void);
+
 static int
 nv40_get_intensity(struct backlight_device *bd)
 {
@@ -74,6 +78,7 @@ nv40_backlight_init(struct drm_connector *connector)
 	struct nvif_object *device = &drm->device.object;
 	struct backlight_properties props;
 	struct backlight_device *bd;
+	char* backlight_name = NULL;
 
 	if (!(nvif_rd32(device, NV40_PMC_BACKLIGHT) & NV40_PMC_BACKLIGHT_MASK))
 		return 0;
@@ -81,8 +86,14 @@ 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,
+	backlight_name = nouveau_get_backlight_name();
+	bd = backlight_device_register(backlight_name , connector->kdev, drm,
 				       &nv40_bl_ops, &props);
+
+	// backlight_device_register() makes a copy
+	kfree(backlight_name);
+	backlight_name = NULL;
+
 	if (IS_ERR(bd))
 		return PTR_ERR(bd);
 	drm->backlight = bd;
@@ -182,6 +193,7 @@ nv50_backlight_init(struct drm_connector *connector)
 	struct backlight_properties props;
 	struct backlight_device *bd;
 	const struct backlight_ops *ops;
+	char* backlight_name = NULL;
 
 	nv_encoder = find_encoder(connector, DCB_OUTPUT_LVDS);
 	if (!nv_encoder) {
@@ -203,8 +215,14 @@ 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,
+	backlight_name = nouveau_get_backlight_name();
+	bd = backlight_device_register(backlight_name, connector->kdev,
 				       nv_encoder, ops, &props);
+
+	// backlight_device_register() makes a copy
+	kfree(backlight_name);
+	backlight_name = NULL;
+
 	if (IS_ERR(bd))
 		return PTR_ERR(bd);
 
@@ -252,3 +270,16 @@ nouveau_backlight_exit(struct drm_device *dev)
 		drm->backlight = NULL;
 	}
 }
+
+static char*
+nouveau_get_backlight_name(void)
+{
+	// 12 chars for "nv_backlight" + 2 for two digits number + 1 for '\0'
+	char* backlight_name = (char*)kmalloc(sizeof(char[15]), GFP_KERNEL);
+	const int nb = atomic_inc_return(&bl_interfaces_nb) - 1;
+	if (nb > 0 && nb < 100)
+		sprintf(backlight_name, "nv_backlight%d", nb);
+	else
+		sprintf(backlight_name, "nv_backlight");
+	return backlight_name;
+}
-- 
2.8.0

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