[PATCH] powermac backlight fixes

Fix a erroneous calculation of the legacy brightness values as reported by
Paul Collins.  Additionally, it moves the calculation of the negative value
in the radeonfb driver after the value check.

Signed-off-by: Michael Hanselmann <linux-kernel@hansmi.ch>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Paul Collins <paul@briny.ondioline.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
index 498b042e1837..c7a27eddca6d 100644
--- a/arch/powerpc/platforms/powermac/backlight.c
+++ b/arch/powerpc/platforms/powermac/backlight.c
@@ -119,7 +119,14 @@ int pmac_backlight_set_legacy_brightness(int brightness)
                 down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
                 props->brightness = brightness *
-                        props->max_brightness / OLD_BACKLIGHT_MAX;
+                        (props->max_brightness + 1) /
+                        (OLD_BACKLIGHT_MAX + 1);
+
+                if (props->brightness > props->max_brightness)
+                        props->brightness = props->max_brightness;
+                else if (props->brightness < 0)
+                        props->brightness = 0;
+
                 props->update_status(pmac_backlight);
                 up(&pmac_backlight->sem);
 
@@ -140,8 +147,11 @@ int pmac_backlight_get_legacy_brightness()
 
                 down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
+
                 result = props->brightness *
-                        OLD_BACKLIGHT_MAX / props->max_brightness;
+                        (OLD_BACKLIGHT_MAX + 1) /
+                        (props->max_brightness + 1);
+
                 up(&pmac_backlight->sem);
         }
         mutex_unlock(&pmac_backlight_mutex);