Rend0e/Fix_MCLK_Clock_Stuck_Arch_Linux_Guide.md

## Fix_MCLK_Clock_Stuck_Arch_Linux_Guide.md

      
    Raw
  

              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]


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


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).


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).


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


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.


Use wxedid to open the generated edid to take note of its values:
yay -S wxedid

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


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.


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


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


Find DTD: Detailed Timing Descriptor


Click the DTD Constructor Tab


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:


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


Click Option on the panel -> Assemble EDID:


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


Load EDID at boot for the particular monitor:


Place the edid file in /lib/firmware/edid
sudo mkdir -p /lib/firmware/edid
sudo cp edid.bin /lib/firmware/edid/edid_modified.bin


Include the custom EDID file in the initramfs
sudoedit /etc/mkinitcpio.conf

FILES=(/lib/firmware/edid/edid_modified.bin)


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


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
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