[PATCH v2] drm/amd/display: set backlight level limit to 1

[Guttula, Suresh]

From: "Guttula, Suresh" <Suresh.Guttula at amd.com>

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 intended behaviour as
per HW constraints.

Signed-off-by: suresh guttula <suresh.guttula at amd.com>
Reviewed-by: Harry Wentland <harry.wentland at amd.com>
---
v2 : comment edited to represent general usecase
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 7 +++++++
 1 file changed, 7 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..be261ef 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 +1518,13 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 {
 	struct amdgpu_display_manager *dm = bl_get_data(bd);
 
+	/*
+	 * PWM interperts 0 as 100% rather than 0% because of HW
+	 * limitation for level 0.So limiting minimum brightness 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