Reddit/Social Media

It's also worth to initiate discussion with Linux graphic stack developers: I sent message to their mailing list.
Please also send your stories around Linux too!
https://lists.freedesktop.org/archives/amd-gfx/2019-July/036310.html

Thanks!

kammerer I tried a post on the amd-gfx mailing list in the start of 2018 and no one responded.

As for Reddit: I feel that Reddit as a platform is going downhill because in part of the influx of "new users" compared to 5 or so years ago, and the fact that Reddit is more "corporate" with advertisements and other negative tactics to make money for the company. I mean look at the controversy with regards to the "redesign". People aren't happy.

In addition I think fragmentation of the userbase across multiple forums isn't a good idea, seeing how we have enough trouble organizing information here already.

What I think should happen (potentially) is that Slacor (owner of this site) should work on SEO (as much as I loathe that term) to ensure the forum ranks higher in search results for relevant keywords. I've already done my own searches and it already ranks highly with links to specific threads for specific keywords.

kammerer

Here's a slightly condescend version of the email I sent on 2018-01-01. I tried going through the archive it seems like it was removed(!)

Hello

I'm inquiring about the amdgpu driver and temporal dithering. Let me
give you a quick overview of the relevant parts of my setup.

Monitor: BenQ GW2760HS (27" VA panel, native 8-bit, no FRC) connected
via DVI
GPU: ASUS R9 270X
OS: Debian 8.x Jessie, also use Ubuntu MATE 16.04

It seems when using the above setup, despite the monitor being 8-bit I
notice on dark grey and gradient images that the pixels are unstable and
are "moving" with vertical banding, a telltale sign of dithering in my
experience.

I know there is supposedly a way to disable dithering on the older fglrx
driver. Unfortunately as fglrx doesn't work with the new Xorg ABI which
newer Linux distributions use I am unable to test it.

https://forums.guru3d.com/threads/how-to-disable-dithering-in-linux.387362/

I cloned the kernel source from this repository and edited some of the
dce_* files under drivers/gpu/drm/amd/amdgpu where it appears there are
case statements that control the dithering done by the GPU (just an
educated case), so said case statements do nothing instead of setting
dithering registers and managed to recompile the kernel. Unfortunately
that didn't seem to disable the temporal dithering so either I've
patched the wrong functions for my GPU or something else. Frankly I
wonder if AMD cards dither by default independent of the running
graphics driver as I think I saw the dithering when I was running Ubuntu
MATE on their grey colored boot screen (Plymouth).

I'll try and a get a microscope and/or hand lens to try and see the LCD
subpixels later.

+++ b/drivers/gpu/drm/amd/amdgpu/dce_v6_0.c
@@ -467,28 +467,6 @@ static void dce_v6_0_program_fmt(struct drm_encoder
*encoder)


        switch (bpc) {
-       case 6:
-               if (dither == AMDGPU_FMT_DITHER_ENABLE)
-                       /* XXX sort out optimal dither settings */
-                       tmp |=
(FMT_BIT_DEPTH_CONTROL__FMT_FRAME_RANDOM_ENABLE_MASK |
-
FMT_BIT_DEPTH_CONTROL__FMT_HIGHPASS_RANDOM_ENABLE_MASK |
-
FMT_BIT_DEPTH_CONTROL__FMT_SPATIAL_DITHER_EN_MASK);
-               else
-                       tmp |= FMT_BIT_DEPTH_CONTROL__FMT_TRUNCATE_EN_MASK;
-               break;

[sic]

        default:
                /* not needed */
                break;

My next goal is to figure out how to do live kernel debugging with
another physical computer to see what functions are being hit in regards
to dithering and color depth (as I could have edited a function that's
not called in the case of the R9 270X I have).

I know the motherboard inside my desktop has several COM port headers so
I might be able to do kernel debugging of the GPU driver with the serial
port and another computer. Something to look into.

As for why I am doing this. First of all I am a photographer (one of
many hobbies) and like having accurate colors in my workflow, second of
all I used to get bad headaches from certain visual stimuli due to
nervous system issues. To keep a long story short I've largely gotten
that taken care of but I'm working on disabling dithering to ensure it's
not something contributing to eye fatiguing. Third of all, it's been an
interesting challenge for myself.

Many thanks

JTL
Actually I've tried made some debugging via logging, but didn't find any interesting in my configuration.
At least you can add DRM_INFO("SOME_PREFIX...")/DRM_DEBUG("SOME_PREFIX...") debug messages in interested function to see what parameters are passed and what logic is performed (or even check is they just executed). Than you can 'grep SOME_PREFIX' them in kern.log. It's also could be worth to enable drm debug logging via 'drm.debug=0xf' in grub boot menu: https://patchwork.kernel.org/patch/3883031/

I've created separate topic to collect our cases. Please join: https://ledstrain.org/d/683-linux-graphics-stack !