arch/powerpc: Remove <linux/fb.h> from backlight code

Replace <linux/fb.h> with a forward declaration in <asm/backlight.h> to
resolve an unnecessary dependency. Remove pmac_backlight_curve_lookup()
and struct fb_info from source and header files. The function and the
framebuffer struct are unused. No functional changes.

v3:
	* Add Fixes tag (Christophe)
	* fix typos in commit message (Jani)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: d565dd3 ("[PATCH] powerpc: More via-pmu backlight fixes")
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> # (powerpc)
Link: https://patchwork.freedesktop.org/patch/msgid/20240306122935.10626-4-tzimmermann@suse.de

Author: Thomas Zimmermann

arch/powerpc/include/asm/backlight.h

@@ -10,15 +10,14 @@
 #define __ASM_POWERPC_BACKLIGHT_H
 #ifdef __KERNEL__
 
-#include <linux/fb.h>
 #include <linux/mutex.h>
 
+struct backlight_device;
+
 /* For locking instructions, see the implementation file */
 extern struct backlight_device *pmac_backlight;
 extern struct mutex pmac_backlight_mutex;
 
-extern int pmac_backlight_curve_lookup(struct fb_info *info, int value);
-
 extern int pmac_has_backlight_type(const char *type);
 
 extern void pmac_backlight_key(int direction);

arch/powerpc/platforms/powermac/backlight.c

@@ -9,7 +9,6 @@
  */
 
 #include <linux/kernel.h>
-#include <linux/fb.h>
 #include <linux/backlight.h>
 #include <linux/adb.h>
 #include <linux/pmu.h>
@@ -72,31 +71,6 @@ int pmac_has_backlight_type(const char *type)
 	return 0;
 }
 
-int pmac_backlight_curve_lookup(struct fb_info *info, int value)
-{
-	int level = (FB_BACKLIGHT_LEVELS - 1);
-
-	if (info && info->bl_dev) {
-		int i, max = 0;
-
-		/* Look for biggest value */
-		for (i = 0; i < FB_BACKLIGHT_LEVELS; i++)
-			max = max((int)info->bl_curve[i], max);
-
-		/* Look for nearest value */
-		for (i = 0; i < FB_BACKLIGHT_LEVELS; i++) {
-			int diff = abs(info->bl_curve[i] - value);
-			if (diff < max) {
-				max = diff;
-				level = i;
-			}
-		}
-
-	}
-
-	return level;
-}
-
 static void pmac_backlight_key_worker(struct work_struct *work)
 {
 	if (atomic_read(&kernel_backlight_disabled))