Steam Deck: Pstate 0 Vid is 161, above max of 124

[coolbho3k]

On the Steam Deck's custom AMD APU (model 90h, family 17h), the value of Pstate 0 is 161.

I'd like to undervolt this state! Would it be safe to raise the value of the MAX_VID macro to something a bit above 161?

Output:

(deck@steamdeck amdctl)$ sudo ./amdctl -g
Detected CPU model 90h, from family 17h with 8 CPU cores (REFCLK = 100MHz ; Voltage ID Encodings: SVI (serial)).

Core 0 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 1 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 2 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 3 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 4 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 5 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 6 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

Core 7 | P-State Limits (non-turbo): Highest: 0 ; Lowest 2 | Current P-State: 0
 Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
      0      1    112      8    161   28.00x  2800.00MHz   543mV     28     10  38.00A   20.63W
      1      1     96      8    114   24.00x  2400.00MHz   837mV     24     10  34.00A   28.46W
      2      1    102     12    105   17.00x  1700.00MHz   893mV     17     10  27.00A   24.11W

[coolbho3k]

Ah it appears that undervolting mobile Zen CPUs may not be possible even through the MSR. Please close if that's the case. I tried manually tweaking the CpuVid limit in code and running amdctl, even setting the VID to some insanely high number, I didn't really seem to notice a difference in either temperatures or get the system to crash due to low voltage.

I noticed as well: weirdly enough the higher P-States on the Deck have lower VIDs?

[coolbho3k]

Yes, I know about Smokeless UMAF. It would be great to be able to control it from Linux, though.

[Arian04]

just an FYI for anyone who comes across this with the same question I had. Yes, you can set MAX_VID to a higher value and build from source. I went through the AMD processor programming reference sheet for my cpu and couldn't find anything there or elsewhere online that indicated that I shouldn't set the core VID higher than 124. I'm guessing the author of this tool might've just thought it was a reasonable limit or something? My laptop hasn't exploded yet so I'm guessing there's no serious reason to not undervolt even harder if your hardware can handle it. If things go badly though, I'll try to remember to update this.

edit: also I was gonna try smokeless umaf but it's not open source and the dev isn't active at all, and I worry about using a potentially dangerous piece of software under those circumstances

also,
hardware: Dell Inspiron 14 5425, Ryzen 5 5625u
current undervolt:

Pstate Status CpuFid CpuDid CpuVid  CpuMult     CpuFreq CpuVolt IddVal IddDiv CpuCurr CpuPower
0      1     92      8    108   23.00x  2300.00MHz   875mV     23     10  33.00A   28.88W
1      1     90     10    124   18.00x  1800.00MHz   775mV     18     10  28.00A   21.70W
2      1     96     12    125   16.00x  1600.00MHz   768mV     16     10  26.00A   19.97W

edit2: actually since the docs im reading and the amdctl source code both agree that for 19h family CPUs, bits 21:14 (8 bits) are used to store the core VID, a true maximum value would be #define MAX_VID 255.

edit3: i didnt check the voltage calculation math before saying that. yea 255 is a true max value, but realistically, something like 165 would be more than reasonable.

edit4: i've just realized that my undervolt isn't doing anything. I've been suspicious about how low I've been able to go, but after seeing issue #18 and installing zenpower, i've confirmed it :(