Gamma problem after 4096 LUT entries change

Gamma problem after 4096 LUT entries change

[Môshe van der Sterre]

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Hello Leo Li,

The current mainline has a gamma regression for me, running wayland on a 
Ryzen 5 2400G (integrated gpu). Colors are much too dark after the 
following commit:
086247a4b2fb "drm/amd/display: Use 4096 lut entries"

 From this commit alone I cannot deduce how to properly address the 
problem. Reverting restores the correct colors. Unfortunately, I have no 
other amdgpu hardware to test if this is specific to the integrated gpu 
or not.

I'll gladly test possible fixes or debug a little further if you can 
point me in the right direction.

Thanks,
Môshe van der Sterre



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Re: Gamma problem after 4096 LUT entries change

[Harry Wentland]

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On 2018-04-15 05:37 AM, Môshe van der Sterre wrote:
> Hello Leo Li,
> 
> The current mainline has a gamma regression for me, running wayland on a Ryzen 5 2400G (integrated gpu). Colors are much too dark after the following commit:
> 086247a4b2fb "drm/amd/display: Use 4096 lut entries"
> 
> From this commit alone I cannot deduce how to properly address the problem. Reverting restores the correct colors. Unfortunately, I have no other amdgpu hardware to test if this is specific to the integrated gpu or not.
> 
> I'll gladly test possible fixes or debug a little further if you can point me in the right direction.
> 

Can you give attached patch a spin. We'll probably merge it or a variant of it soon.

Harry

> Thanks,
> Môshe van der Sterre
> 
> 

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>From 9adc614f258ba021aa70eeed92ecb0613406cf09 Mon Sep 17 00:00:00 2001
From: Harry Wentland <harry.wentland-5C7GfCeVMHo@public.gmane.org>
Date: Thu, 12 Apr 2018 16:37:09 -0400
Subject: [PATCH] drm/amd/display: Don't program bypass on linear regamma LUT

Even though this is required for degamma since DCE HW only supports a
couple predefined LUTs we can just program the LUT directly.

This fixes dark screens which occurs when we program regamma to bypass
while degamma is using srgb LUT.

Signed-off-by: Harry Wentland <harry.wentland-5C7GfCeVMHo@public.gmane.org>
---
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c  | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
index ef5fad8c5aac..59e993ad1209 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
@@ -133,19 +133,15 @@ int amdgpu_dm_set_regamma_lut(struct dm_crtc_state *crtc)
 		/* By default, use the SRGB predefined curve.*/
 		stream->out_transfer_func->type = TF_TYPE_PREDEFINED;
 		stream->out_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
+
+		DRM_DEBUG_KMS("Using pre-defined regamma\n");
+
 		return 0;
 	}
 
 	lut = (struct drm_color_lut *)blob->data;
 	lut_size = blob->length / sizeof(struct drm_color_lut);
 
-	if (__is_lut_linear(lut, lut_size)) {
-		/* Set to bypass if lut is set to linear */
-		stream->out_transfer_func->type = TF_TYPE_BYPASS;
-		stream->out_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
-		return 0;
-	}
-
 	gamma = dc_create_gamma();
 	if (!gamma)
 		return -ENOMEM;
@@ -161,6 +157,8 @@ int amdgpu_dm_set_regamma_lut(struct dm_crtc_state *crtc)
 		return -EINVAL;
 	}
 
+	DRM_DEBUG_KMS("Using regamma with %d entries\n", lut_size);
+
 	/* Convert drm_lut into dc_gamma */
 	__drm_lut_to_dc_gamma(lut, gamma, gamma->type == GAMMA_RGB_256);
 
-- 
2.17.0


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Re: Gamma problem after 4096 LUT entries change

[Môshe van der Sterre]

On 04/16/2018 04:07 PM, Harry Wentland wrote:
> On 2018-04-15 05:37 AM, Môshe van der Sterre wrote:
>> Hello Leo Li,
>>
>> The current mainline has a gamma regression for me, running wayland on a Ryzen 5 2400G (integrated gpu). Colors are much too dark after the following commit:
>> 086247a4b2fb "drm/amd/display: Use 4096 lut entries"
>>
>>  From this commit alone I cannot deduce how to properly address the problem. Reverting restores the correct colors. Unfortunately, I have no other amdgpu hardware to test if this is specific to the integrated gpu or not.
>>
>> I'll gladly test possible fixes or debug a little further if you can point me in the right direction.
>>
> Can you give attached patch a spin. We'll probably merge it or a variant of it soon.
>
> Harry
Thank you Harry. The patch works on my system.
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