[PATCH] drm/amd: Don't fail on backlight = 0

[Deucher, Alexander]

Acked-by: Alex Deucher <alexander.deucher at amd.com>

________________________________
From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> on behalf of David Francis <David.Francis at amd.com>
Sent: Tuesday, November 6, 2018 11:14:46 AM
To: amd-gfx at lists.freedesktop.org
Cc: Francis, David; Samantham at posteo.net; Wentland, Harry; Guttula, Suresh
Subject: [PATCH] drm/amd: Don't fail on backlight = 0

Amgpu's backlight update status function was
returning 1 (an error value) when the backlight
property was 0.  This breaks users that assume
0 is a valid backlight value (which is a
correct assumption)

If the user passes in a backlight value of 0,
tell them everything is fine, then write a value of
1 to hardware.

Signed-off-by: David Francis <David.Francis at amd.com>
Bugzilla: https://bugs.freedesktop.org/108668
Fixes: 416615ea9578 ("drm/amd/display: set backlight level limit to 1")
Cc: Suresh.Guttula at amd.com
Cc: Harry.Wentland at amd.com
Cc: Samantham at posteo.net
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c  | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

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 f8ec8a146663..131e6483d442 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1567,21 +1567,23 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 {
         struct amdgpu_display_manager *dm = bl_get_data(bd);

+       /* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
+        * and 16 bit fractional, where 1.0 is max backlight value.
+        * bd->props.brightness is 8 bit format and needs to be converted by
+        * scaling via copy lower byte to upper byte of 16 bit value.
+        */
+       uint32_t brightness = bd->props.brightness * 0x101;
+
         /*
          * PWM interperts 0 as 100% rather than 0% because of HW
-        * limitation for level 0.So limiting minimum brightness level
+        * limitation for level 0.  So limiting minimum brightness level
          * to 1.
          */
         if (bd->props.brightness < 1)
-               return 1;
+               brightness = 0x101;

-       /* backlight_pwm_u16_16 parameter is in unsigned 32 bit, 16 bit integer
-        * and 16 bit fractional, where 1.0 is max backlight value.
-        * bd->props.brightness is 8 bit format and needs to be converted by
-        * scaling via copy lower byte to upper byte of 16 bit value.
-        */
         if (dc_link_set_backlight_level(dm->backlight_link,
-                       (bd->props.brightness * 0x101), 0, 0))
+                       brightness, 0, 0))
                 return 0;
         else
                 return 1;
--
2.17.1

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