[REGRESSION] Too-low frequency limit for AMD GPU PCI-passed-through to Windows VM

[Lazar, Lijo]

On 1/25/2022 5:28 AM, James Turner wrote:
> Hi Lijo,
> 
>> Not able to relate to how it affects gfx/mem DPM alone. Unless Alex
>> has other ideas, would you be able to enable drm debug messages and
>> share the log?
> 
> Sure, I'm happy to provide drm debug messages. Enabling everything
> (0x1ff) generates *a lot* of log messages, though. Is there a smaller
> subset that would be useful? Fwiw, I don't see much in the full drm logs
> about the AMD GPU anyway; it's mostly about the Intel GPU.
> 
> All the messages in the system log containing "01:00" or "1002:6981" are
> identical between the two versions.
> 
> I've posted below the only places in the logs which contain "amd". The
> commit with the issue (f9b7f3703ff9) has a few drm log messages from
> amdgpu which are not present in the logs for f1688bd69ec4.
> 
> 
> # f1688bd69ec4 ("drm/amd/amdgpu:save psp ring wptr to avoid attack")
> 
> [drm] amdgpu kernel modesetting enabled.
> vga_switcheroo: detected switching method \_SB_.PCI0.GFX0.ATPX handle
> ATPX version 1, functions 0x00000033
> amdgpu: CRAT table not found
> amdgpu: Virtual CRAT table created for CPU
> amdgpu: Topology: Add CPU node
> 
> 
> # f9b7f3703ff9 ("drm/amdgpu/acpi: make ATPX/ATCS structures global (v2)")
> 
> [drm] amdgpu kernel modesetting enabled.
> vga_switcheroo: detected switching method \_SB_.PCI0.GFX0.ATPX handle
> ATPX version 1, functions 0x00000033
> [drm:amdgpu_atif_pci_probe_handle.isra.0 [amdgpu]] Found ATIF handle \_SB_.PCI0.GFX0.ATIF
> [drm:amdgpu_atif_pci_probe_handle.isra.0 [amdgpu]] ATIF version 1
> [drm:amdgpu_acpi_detect [amdgpu]] SYSTEM_PARAMS: mask = 0x6, flags = 0x7
> [drm:amdgpu_acpi_detect [amdgpu]] Notification enabled, command code = 0xd9
> amdgpu: CRAT table not found
> amdgpu: Virtual CRAT table created for CPU
> amdgpu: Topology: Add CPU node
> 
> 

Hi James,

Specifically, I was looking for any events happening at these two places 
because of the patch-

https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c#L411

https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c#L653

The patch specifically affects these two. On/before starting VM, if 
there are invocations of these two functions on your system as a result 
of the patch, we could navigate from there and check what is the side 
effect.

Thanks,
Lijo

> Other things I'm willing to try if they'd be useful:
> 
> - I could update to the 21.Q4 Radeon Pro driver in the Windows VM. (The
>    21.Q3 driver is currently installed.)
> 
> - I could set up a Linux guest VM with PCI passthrough to compare to the
>    Windows VM and obtain more debugging information.
> 
> - I could build a kernel with a patch applied, e.g. to disable some of
>    the changes in f9b7f3703ff9.
> 
> James
>