AMD PMF Policy Binary Support Queued For Linux 6.8

As part of AMD's Platform Management Framework (PMF) and working on new Ryzen features like the Smart PC Solutions Builder, a set of patches are queued up ahead of the Linux 6.8 kernel cycle support for policy binary support with the PMF driver.

The AMD PMF Policy Binary support has been queued into the platform-drivers-x86 tree's for-next branch ahead of the Linux 6.8 merge window opening up on 8 January. The AMD PMF Policy Binary support is self-described in a patch as:

PMF Policy binary is a encrypted and signed binary that will be part of the BIOS. PMF driver via the ACPI interface checks the existence of Smart PC bit. If the advertised bit is found, PMF driver walks the acpi namespace to find out the policy binary size and the address which has to be passed to the TA during the TA init sequence.

The policy binary is comprised of inputs (or the events) and outputs (or the actions). With the PMF ecosystem, OEMs generate the policy binary (or could be multiple binaries) that contains a supported set of inputs and outputs which could be specifically carved out for each usage segment (or for each user also) that could influence the system behavior either by enriching the user experience or/and boost/throttle power limits.
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Example policies:

1) if slider is performance ; set the SPL to 40W Here PMF driver registers with the platform profile interface and when the slider position is changed, PMF driver lets the TA know about this. TA sends back an action to update the Sustained Power Limit (SPL). PMF driver updates this limit via the PMFW mailbox.

2) if user_away ; then lock the system Here PMF driver hooks to the AMD SFH driver to know the user presence and send the inputs to TA and if the condition is met, the TA sends the action of locking the system. PMF driver generates a uevent and based on the udev rule in the userland the system gets locked with systemctl.

The intent here is to provide the OEM's to make a policy to lock the system when the user is away ; but the userland can make a choice to ignore it.

The OEMs will have an utility to create numerous such policies and the policies shall be reviewed by AMD before signing and encrypting them. Policies are shared between operating systems to have seemless user experience.

Having these different policies as cross-platform/OS-independent blobs is nice for enhancing the Linux support with these sort of features typically otherwise not being supported on Linux by the vendor. Though it may rub some users the wrong way given that the policy binaries are encrypted and in effect black boxes. For AMD's part they are signed and encrypted since otherwise these binaries could potentially put the hardware out of spec and cause damage, similar to the encrypted handling of power management related features on the AMD Ryzen side.

In any event now that the PMF Policy Binary patches are in their "for-next" branch means it's on the way for finding this support in Linux 6.8. It's not currently clear if any current AMD Ryzen platforms are making use of policy binaries or if this is a feature coming with next-generation Ryzen systems.