Fix AMD GPU high idle power MCLK (vram / memory clock) stuck at 96 MHz / 1000 MHz for high refresh rates on Arch Linux Wayland & Xorg

Fix_MCLK_Clock_Stuck_Arch_Linux_Guide.md

Fix AMD GPU high idle power MCLK (vram / memory clock) stuck at 96 MHz / 1000 MHz for high refresh rates on Arch Linux Wayland & Xorg

On certain resolutions & refresh rates or multi-monitor setups, you might have noticed that your GPU MCLK (vram / memory clock) is stuck at the highest clock frequency (1000 MHz) [1] [2] causing higher GPU idle power draw. On Linux kernel 6.4.x, AMDGPU MCLK (vram/memory) clocks at the lowest, causing major FPS drops while gaming [1] [2]. This is likely due to a monitor not using Coordinated Video Timings (CVT) with a low V-Blank value for the affected resolutions & refresh rates. The higher clocking behavior is due to:

Well, the reason the clocks get forced to max in some cases is to avoid the flickering you are seeing. There is a certain latency required to change the mclk. The hardware needs to hide that mclk switch during some blanking period of the display otherwise you would see flickering. If the blanking periods are too short or not alignable (in the case of multiple displays), the driver has to use a fixed mclk to avoid the flickering. In your case, it appears that the latency of switching to/from the 96Mhz mclk is right on the edge of what is possible given the monitors blanking periods. You may need to slightly lengthen the hblank or vblank periods in your display's modeline.

The monitor's non standard timings values were likely set that way to keep its pixel clock values within display cable bandwidth constraints that are more relevant on higher resolutions & refresh rates, which is why this issue tends to occur on high resolutions & refresh rates.

HDMI

Version	Limit	Data rate	Bandwidth
1.0-1.2a	165 MHz	3.96 Gbps	4.95 Gbps
1.3-1.4b	340 MHz*	8.16 Gbps	10.2 Gbps
2.0-2.0b	600 MHz	14.4 Gbps	18 Gbps

DisplayPort

Check https://www.monitortests.com/blog/common-pixel-clock-limits/

Check for issue

You can check for this issue by monitoring your GPU MCLK/VRAM/Memory clock value with nvtop, mangohud or cat /sys/class/drm/card0/device/pp_dpm_mclk (Note: try card1 if file is not found). If it's stuck at the highest clock (1000 MHz), you would also notice a higher idle power draw. If the values are stuck and do not adapt to the GPU workload, try lowering the display resolution refresh rate to see if it resolves the issue. If the issue only occurs in specific resolutions & refresh rates, then it's likely that the monitor's EDID has a too low v-blank value for the specific resolution & refresh rate.

Fix for Xorg [1]

1. Use cvt_modeline_calculator_12 to obtain modeline values for your resolution & refresh rate with CVT v1.2 reduced blanking timings:

   curl https://raw.githubusercontent.com/kevinlekiller/cvt_modeline_calculator_12/master/cvt12.c --output cvt12.c
   gcc cvt12.c -O2 -o cvt12 -lm -Wall
   ./cvt12 1920 1080 144 -b

   Note: change 1920 1080 144 to your resolution and refresh rate, mine is 1920x1080@144.

   Output Example:

   # 1920x1080 @ 144.000 Hz Reduced Blank (CVT) field rate 144.000 Hz; hsync: 166.608 kHz; pclk: 333.22 MHz
   Modeline "1920x1080_144.00_rb2"  333.22  1920 1928 1960 2000  1080 1143 1151 1157 +hsync -vsync

2. Use xrandr to add the custom resolution modeline:

   xrandr --newmode "MCLK-fix" 333.22  1920 1928 1960 2000  1080 1143 1151 1157 +hsync -vsync
   xrandr --addmode HDMI-2 "MCLK-fix"
   

   Note: replace values after "MCLK-fix" with the modeline values output from step 1 and replace HDMI-2 with your connector (run xrandr).

3. Select the resolution and check if MCLK (VRAM / Memory) clock frequency properly adjusts to GPU workloads.

Fix for Wayland

Before proceeding, try temporarily switching to xorg to test if the xorg solution works. You can skip steps 1-3 if you find your resolution & refresh rate in Some CVT-RB v2 EDID values (can use this to skip steps 1-3).

1. Use cvt_modeline_calculator_12 to obtain modeline values for your resolution & refresh rate with CVT v1.2 reduced blanking timings:

   curl https://raw.githubusercontent.com/kevinlekiller/cvt_modeline_calculator_12/master/cvt12.c --output cvt12.c
   gcc cvt12.c -O2 -o cvt12 -lm -Wall
   ./cvt12 1920 1080 144 -b

   Note: change 1920 1080 144 to your resolution and refresh rate, mine is 1920x1080@144Hz:

   Output Example:

   # 1920x1080 @ 144.000 Hz Reduced Blank (CVT) field rate 144.000 Hz; hsync: 166.608 kHz; pclk: 333.22 MHz
   Modeline "1920x1080_144.00_rb2"  333.22  1920 1928 1960 2000  1080 1143 1151 1157 +hsync -vsync

2. Parse the modeline to edid-generator to see its values in EDID binary format:

   git clone https://github.com/akatrevorjay/edid-generator.git
   cd edid-generator
   yay -S zsh edid-decode-git automake dos2unix # Required dependencies for edid-generator
   zsh # Need to enter zsh shell
   ./modeline2edid - <<< 'Modeline "MCLK-fix" 333.22  1920 1928 1960 2000  1080 1143 1151 1157 +hsync -vsync'
   make

   Note: replace the values after "MCLK-fix" with the modeline values output from step 1.

3. Use wxedid to open the generated edid to take note of its values:

   yay -S wxedid

   1. Open the MCLK-Fix.bin file with wxEDID (/usr/bin/wxedid).
   2. You may get an error message, so follow its prompt: Options->"Ignore EDID Errors" and then "Reparse EDID buffer" to view the data anyway.
   3. Find DTD: Detailed Timing Descriptor.
   4. Take note of the values or take a screenshot. Example:

4. Obtain your monitor's EDID binary file:

   ls /sys/class/drm/ # Use xrandr, wlr-randr, gnome-randr-rust to find the correct connector.
   cat /sys/class/drm/card1-HDMI-A-2/edid # Check for an output (monitor name may be visible). 
   cp /sys/class/drm/card1-HDMI-A-2/edid edid.bin # Replace card1-HDMI-A-2 with your connector.

   

5. Use wxEDID to edit mointor's EDID to MCLK-fix's values:

   1. Open the edid.bin file with wxEDID (/usr/bin/wxedid)

   2. Find DTD: Detailed Timing Descriptor

   3. Click the DTD Constructor Tab

      

   4. Check if X-res, V-res and V-Refresh matches your resolution and refresh rate; if not, go back to the EDID tab, then keep checking another DTD until you find it:

   5. Go back to the EDID tab and change the values to match the ones in MCLK-Fix.bin:

   6. Click Option on the panel -> Assemble EDID:

      

   7. Click File on the panel -> Save EDID binary (overwrite edid.bin):

      

6. Load EDID at boot for the particular monitor:

   1. Place the edid file in /lib/firmware/edid

      sudo mkdir -p /lib/firmware/edid
      sudo cp edid.bin /lib/firmware/edid/edid_modified.bin

   2. Include the custom EDID file in the initramfs

      sudoedit /etc/mkinitcpio.conf
      
      FILES=(/lib/firmware/edid/edid_modified.bin)

   3. Add the kernel parameter drm.edid_firmware=HDMI-A-2:edid/edid_modified.bin (replace HDMI-A-2 with your connector).

7. Reboot and check if MCLK (VRAM / Memory) clock frequency properly adjusts to GPU workloads.

Some CVT-RB v2 EDID values

1920x1080@60Hz

Modeline "1920x1080_60.00_rb2" 133.32 1920 1928 1960 2000 1080 1097 1105 1111 +hsync -vsync

1920x1080@120Hz

Modeline "1920x1080_120.00_rb2" 274.56 1920 1928 1960 2000 1080 1130 1138 1144 +hsync -vsync

1920x1080@144Hz

Modeline "1920x1080_144.00_rb2" 333.22 1920 1928 1960 2000 1080 1143 1151 1157 +hsync -vsync

1920x1080@160Hz

Modeline "1920x1080_160.00_rb2" 373.12 1920 1928 1960 2000 1080 1152 1160 1166 +hsync -vsync

1920x1080@240Hz

Modeline "1920x1080_240.00_rb2" 583.20 1920 1928 1960 2000 1080 1201 1209 1215 +hsync -vsync

2560×1440@60Hz

Modeline "2560x1440_60.00_rb2" 234.59 2560 2568 2600 2640 1440 1467 1475 1481 +hsync -vsync

2560×1440@120Hz

Modeline "2560x1440_120.00_rb2" 483.12 2560 2568 2600 2640 1440 1511 1519 1525 +hsync -vsync

2560×1440@144Hz

Modeline "2560x1440_144.00_rb2" 586.59 2560 2568 2600 2640 1440 1529 1537 1543 +hsync -vsync

I want to add that when using hyprland, you do not need to modify your edid.

monitor=$monitor1,modeline 1025.80 2560 2568 2600 2640 1440 1605 1613 1619 +hsync -vsync,$moreoptionshere

Important to not double space.

Edit: currently broken with the new implementation of aquamarine: hyprwm/Hyprland#6953

I got extreme flickering with the modeline generated by that program, but then looking at the issues in the project I found that it's a patched fork of an upstream tool I had installed already.

Using cvt -r 5120 1440 240 I got a modeline to add to sway

output "DP-2" {
    modeline  2051.00  5120 5168 5200 5280  1440 1443 1453 1619 +hsync -vsync
    adaptive_sync on
}

My memory clock has dropped from 1.2 GHz to around 400MHz and my power draw from 45-50W to 25-30W. Amazing!

I recall LOTS of people having trouble with the Samsung G9 and magic EDID files being passed around (and they didn't work for me). This should spread!

Maybe even add automatic generation of "proper" modelines to the compositor

Weirdly even though my laptop should be able to drive 2560x1440@165hz I see this whenever I try

[  1306.592] (--) AMDGPU(0): HDMI max TMDS frequency 340000KHz
[  1307.265] (EE) AMDGPU(0): failed to set mode: Cannot allocate memory
[  1307.292] (EE) AMDGPU(0): drmmode_do_crtc_dpms cannot get last vblank counter
[  1345.603] (EE) AMDGPU(0): failed to set mode: Cannot allocate memory
[  1345.631] (EE) AMDGPU(0): drmmode_do_crtc_dpms cannot get last vblank counter

Graphic card memory is set to like 4Gb

looking for the parameters for a 7680x2160 240Hz monitor. Thanks alot

I just use this kernel parameter

video=DP-3:1920x1080MR@164

this one much more easier

https://docs.kernel.org/fb/modedb.html

My monitor doesn't appear to have DTD for 3840x2160@144Hz (only with that resolution and 60Hz...) and when I open the MCLK-fix.bin with the values I previously obtained, the refresh rate and pixel clock are approximately half of what I expect them to be (71.75 instead of 144 Hz and 650.85 instead of 1306.21 MHz)