Obtaining register states from Windows

[mkopec]

I don't have access to many DCN generations on hand. To make developing for other DCN generations simpler, I created a script to dump register states: https://github.com/mkopec/dcn_regdump

We need to collect DCN register states from a Windows VM with the GPU passed through and with the HDMI cable connected, working in FRL mode. This way we can check what the Windows driver does and try to replicate the behavior in Linux.

Any help is greatly appreciated! Instructions are outlined in the README :)

So far I have collected logs from:

• DCN 4.0.1 (RX 9000 series)
• DCN 3.2.1 (RX 7600)
• DCN 3.1.5 (Granite Ridge)

[Leon-Swains]

Just to confirm, I have a 9070XT, you DONT need me to get my register values since you already have 4.0.1?

[mkopec]

Correct, no need :) I'm looking to have a complete set of register states from all DCN gens, to get a complete picture of what we need to do

[Leon-Swains]

Alright, I still have friends with AMD cards. I’ll try to see if they can dump their DCNs. I feel like it would be useful for you to make a public spreadsheet of all the generations you have/don’t have.

[mkopec]

And to reiterate, I'm basically looking for Windows register dumps. I don't really need ones from Linux with FRL not working. I'll update the OP

[Leon-Swains]

I understand, I read the readme. I have a 7600x3d with an iGPU, I’ll definitely try to get the DCNs from that.

[gladiac]

I still have a 7800xt laying around which I could put back into my pc.( I recently upgraded it for a 9070xt before prices got crazy.) I will try to give you a dump of it in the coming week. Probably Wednesday.

[Aviana]

Your script is written for single GPU pass-through i assume. Because it picks up the iGPU i am using for the Linux desktop instead of my 6900XT.

[mkopec]

@Aviana You're right, I forgot multi-gpu setups exist, apparently. Pushed a change that should detect multiple GPUs

[Aviana]

The 6900XT announces itself as DCN 3.0 which gets not picked up by your script. I hardcoded it to 3.0.0 which should be the correct one and got the following output:

`Multiple AMD GPUs found:
[0] 0000:03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Navi 21 [Radeon RX 6800/6800 XT / 6900 XT] (rev c0)
[1] 0000:11:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Granite Ridge [Radeon Graphics] (rev cb)
Select GPU [0-1]: 0
Using AMD GPU at 0000:03:00.0
Found resource file at /sys/bus/pci/devices/0000:03:00.0/resource
Using BAR5 at 0x00000000df900000
Detected DCN version: 3.0.0
Offset file: /home/avi/dcn_regdump-master/dcn_reg/dcn_3_0_0_offset.h
SH mask file: /home/avi/dcn_regdump-master/dcn_reg/dcn_3_0_0_sh_mask.h
Register prefix: reg
Loading registers from: /home/avi/dcn_regdump-master/dcn_reg/dcn_3_0_0_offset.h

====HDMICHARCLOCK====
regHDMICHARCLK0_CLOCK_CNTL: 0x00000000
HDMICHARCLK0_EN: 0
HDMICHARCLK0_SRC_SEL: 0

====HDMI====
regHDMICHARCLK0_CLOCK_CNTL: 0x00000000
HDMICHARCLK0_EN: 0
HDMICHARCLK0_SRC_SEL: 0
`

[mkopec]

ehh, the DCN 3.0.x register definition files are stripped of almost anything related to HDMI 2.1. I haven't added all the definitions back yet, because I haven't figured out the correct VPG and AFMT indexes and if anything else is missing. You might have more success dumping regs from the integrated granite ridge iGPU

[Aviana]

I don't know if its the fact that i am binding the GPU early to the vfio driver but i am just getting zero values / permission denied with the iGPU.

dcn_regdump.20260223-114036.log

[mkopec]

maybe it's picking the wrong BAR? Could you run sudo lspci -vvvs 11:00.0?

[Aviana]

Looks good to me:

11:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Granite Ridge [Radeon Graphics] (rev cb) (prog-if 00 [VGA controller]) Subsystem: ASRock Incorporation Device 364e Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+ Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort+ <TAbort- <MAbort- >SERR- <PERR- INTx- Latency: 0, Cache Line Size: 64 bytes Interrupt: pin A routed to IRQ 69 IOMMU group: 28 Region 0: Memory at fcf0000000 (64-bit, prefetchable) [size=256M] Region 2: Memory at dec00000 (64-bit, prefetchable) [size=2M] Region 4: I/O ports at e000 [size=256] Region 5: Memory at df100000 (32-bit, non-prefetchable) [size=512K] Capabilities: <access denied> Kernel driver in use: amdgpu Kernel modules: amdgpu

[mkopec]

hmm... maybe you need to boot with iomem=relaxed in the kernel commandline