Intel confirmed no dithering on Intel arc a770

WhisperingWind

modesetting includes 2D acceleration. fbdev doesn't and it's more basic.

fbdev also has backlight control.

I think fbdev has a lower chance of creating strain.

https://www.perplexity.ai/search/does-xf86-video-modesetting-ha-hHguh0i_TmqP0XBMZEmHdw

But it could also be because of the higher refresh rate(77hz) in 18.04 vs (60hz) in 22.04.

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I tried latest ubuntu with my Intel iGPU 12900K and it was bad, dithering almost instant feeling. Tried with latest Fedora, looks like no issues, i'm still testing.

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simplex

Hello simplex, happy new year!

I have this mini-PC: https://www.tecno-mobile.com/pc-tablets/product-detail/product/mega-mini-m1

Processor: i5-12450H, Graphics: Intel UHD 48EU (Xe arch), RAM: 2 × DDR4 3200 8 GB Lexar LD4S08G32C22ST. It was connected via type-c (DP) and HDMI. The display used was Sony TV (8+FRC), BenQ BL2711U (8+FRC) and BenQ GL2450 (6+FRC).

This mini PC has a two true HDMI ports. However, there are two Type-C ports that operate in DP mode. When using a true 8-bit monitor, my eyes felt comfortable.

Cons:

• It has a VERY noisy cooling system (IMHO).
• the processor receives about 38.6 watts maximum (I saw this figure in some reviews), which prevents the CPU from performing at 100% of its capabilities.

Pros:

• The absence of dithering in Linux/Windows (tested only on Windows 11).
• The ability to switch to 6-bit video output mode in both Windows 11 and Linux without enabling dithering. I am visiting relatives, and I brought this mini-PC with me. I'm currently testing it with one of my relatives' monitors, the BenQ BL2420PT (6bit+FRC), in 6-bit video output mode on Windows 11 23H2. For now, this is the only way for me to work with this monitor, as I couldn't switch my relatives' PC (i5-12400, UHD 730) to 6-bit mode without enabling dithering, just like my ARC A770. Later, I will compare it with Ubuntu Linux on the same monitor in 6-bit video output mode.

WhisperingWind my relatives' PC (i5-12400, UHD 730)

Could you please check, whats motherboard they use (incl BIOS ver), which DDR4 model names (freq, timings)…? 12400 is okay for your taste, does they use iGPU only?

simplex

Culd you please check, whats motherboard they use (incl BIOS ver), which DDR4 model names (freq, timings)…?

does they use iGPU only?

Gigabyte B760M Gaming X DDR4 motherboard, i5-12400 CPU. Samsung DDR4 RAM: inexpensive green modules of 16 and 8 gigabytes at 2666 MHz, with timings of 20-19-19; support for XMP profiles is absent. To connect to the monitor, UHD 730 is used (a discrete graphics card is absent). The BIOS version is F3 (2023).

Win10 22H2 2022 Update.

Dithering is not present out of the box (I read the video pipeline status register to confirm this).

12400 is okay for your taste?

When using pc of my relative with the BenQ BL2420PT monitor, eyes strain is noticeable. I think it's because of the monitor's FRC, as I experience the same level of eye strain when connecting the mini-PC in 8-bit mode. However, when switching mini-PC to 6-bit, it becomes more comfortable to work: Windows 11 provides maximum comfort, while in Linux Ubuntu, there's slight eye strain but within acceptable limits.

Please keep in mind that I spend about 3 hours a day in front of this monitor, no more than that.

At my relatives' place, this is the best monitor; the others are even worse Therefore, there's no way to properly test the setup based on the i5-12400.

Ivan_P

This is an Intel-specific fix. I'm making this switch in Windows 11 by slightly modifying the source code of the ditherig application in Visual Studio. I write a specific value to the hardware register of the video chip, thereby switching it to 6-bit mode. This works in Windows 11 only with my Intel UHD 48EUs, but it doesn't work with Intel UHD630, Intel UHD730, and Intel ARC A770. If you need technical details, I can provide them.

P.S. I don't know yet why it doesn't work on the UHD 730 (i5-12400), since the i5-12400 also has the Xe video chip architecture, similar to the Intel UHD 48EUs. It might be an issue with the installed version of the driver or something else.

simplex

Link to the guide: https://cdrdv2-public.intel.com/703047/intel-gfx-prm-osrc-tgl-vol-02-c-command-reference-registers-part-2.pdf

On page 692 of the guide, it is stated that bits 5-7 of the register are the Dithering BPC bits, and the 4th bit is the Dithering Enable bit. This means that bits 5-7 set the color depth for dithering. According to my experiments, no matter what values I set for bits 5-7, there is no effect on the i5-12400 (UHD 730) as long as the 4th bit is zero, meaning dithering is off. However, if the 4th bit is set to one, enabling dithering, then bits 5-7 can be used to adjust dithering depth. But this is not what we need, as we actually want to get rid of dithering.

However, when attempting to change bits 5-7 for the Intel UHD 48EUs (i5-12450H), the color depth of the output signal changes, while the Dithering Enable bit (the 4th bit) remains set to zero. This behavior is different from the desktop i5-12400 iGPU.

However, I was led to these experiments after reading a comment in the Linux kernel in the i915 module. It stated:

For Display < 13, Bits 5-7 of PIPE MISC represent DITHER BPC with valid values of: 6, 8, 10 BPC.

ADLP+, the bits 5-7 represent PORT OUTPUT BPC with valid values of: 6, 8, 10, 12 BPC.

I know that there is a way to switch to true 6-bit on the Alder Lake i5-12400, as the i915 module in Linux does this. However, in Linux, this is done through the convenient xrandr tool, and I'm not ready to say which other registers are involved in this process.

WhisperingWind ADLP+, the bits 5-7 represent PORT OUTPUT BPC

Perhabs, this mean Alder Lake and later (12gen+), use another registers for dithering, when 5-7 used for port output bit depth:

Till DISPLAY12 the PIPE_MISC bits 5-7 are used to set the
Dithering BPC, with valid values of 6, 8, 10 BPC.
For ADLP+ these bits are used to set the PORT OUTPUT BPC, with valid
values of: 6, 8, 10, 12 BPC, and need to be programmed whether
dithering is enabled or not.