While refactoring of backlight control code in commit [a95735569:
drm/i915: Refactor panel backlight controls], the handling of the bit
0 of duty-cycle was gone except for pineview.  This resulted in invalid
register values for old chips like 915GM.  When the bit 0 is set, the
backlight is turned off suddenly.

This patch changes the bit-0 check by replacing with the condition of
gen < 4 (pineview is included in this condition, too).

Reported-and-tested-by: Daniel Mack <zon...@gmail.com>
Cc: <sta...@kernel.org>
Signed-off-by: Takashi Iwai <ti...@suse.de>
---
 drivers/gpu/drm/i915/intel_panel.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_panel.c 
b/drivers/gpu/drm/i915/intel_panel.c
index 499d4c0..737d00f 100644
--- a/drivers/gpu/drm/i915/intel_panel.c
+++ b/drivers/gpu/drm/i915/intel_panel.c
@@ -178,12 +178,10 @@ u32 intel_panel_get_max_backlight(struct drm_device *dev)
        if (HAS_PCH_SPLIT(dev)) {
                max >>= 16;
        } else {
-               if (IS_PINEVIEW(dev)) {
+               if (INTEL_INFO(dev)->gen < 4) {
                        max >>= 17;
                } else {
                        max >>= 16;
-                       if (INTEL_INFO(dev)->gen < 4)
-                               max &= ~1;
                }
 
                if (is_backlight_combination_mode(dev))
@@ -203,7 +201,7 @@ u32 intel_panel_get_backlight(struct drm_device *dev)
                val = I915_READ(BLC_PWM_CPU_CTL) & BACKLIGHT_DUTY_CYCLE_MASK;
        } else {
                val = I915_READ(BLC_PWM_CTL) & BACKLIGHT_DUTY_CYCLE_MASK;
-               if (IS_PINEVIEW(dev))
+               if (INTEL_INFO(dev)->gen < 4)
                        val >>= 1;
 
                if (is_backlight_combination_mode(dev)) {
@@ -246,7 +244,7 @@ static void intel_panel_actually_set_backlight(struct 
drm_device *dev, u32 level
        }
 
        tmp = I915_READ(BLC_PWM_CTL);
-       if (IS_PINEVIEW(dev)) {
+       if (INTEL_INFO(dev)->gen < 4) {
                tmp &= ~(BACKLIGHT_DUTY_CYCLE_MASK - 1);
                level <<= 1;
        } else
-- 
1.7.7
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