[PATCH] drm/amd/display: set backlight level limit to 1

["Guttula, Suresh" <Suresh.Guttula-5C7GfCeVMHo@public.gmane.org>]

This patch will work as workaround for silicon limitation
related to PWM dutycycle when the backlight level goes to 0.

Actually PWM value is 16 bit value and valid range from 1-65535.
when ever user requested to set this PWM value to 0 which is not
fall in the range, in VBIOS taken care this by limiting to 1.
This patch here will do the same. Either driver or VBIOS can not
pass 0 value as it is not a valid range for PWM and it will
give a high PWM pulse which is not the intented behaviour as
per HW constraints.

Signed-off-by: suresh guttula <suresh.guttula@amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 492230c..38f84b2 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1518,6 +1518,14 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 {
 	struct amdgpu_display_manager *dm = bl_get_data(bd);
 
+	/*
+	 * When we use brightness low key to reduce the brightness,
+	 * brightness level reaching to 0, with which we can see flash
+	 * screen on ui beacuse of HW limitation.To avoid that  we are
+	 * limiting level to 1
+	 */
+	if (bd->props.brightness < 1)
+		return 1;
 	if (dc_link_set_backlight_level(dm->backlight_link,
 			bd->props.brightness, 0, 0))
 		return 0;
-- 
2.7.4

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