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SubjectRe: [External] RE: [RFC] Documentation: Add documentation for new performance_profile sysfs class

On 2020-10-05 12:56 p.m., Limonciello, Mario wrote:
>>> When implemented for the two vendors mentioned here, it would be using a
>>> proprietary "firmware API" implemented by those two vendors. For example
>> write
>>> arguments (0x1, 0x2) to ACPI-WMI method WMFT and it will cause firmware to
>> coordinate
>>> using undisclosed protocol to affect the platform changes desirable.
>>> This is different in my mind from "kernel writes to a specific register" to
>> set
>>> power properties of a specific device.
>> Just curious on this point - isn't that (mostly) what all hardware does?
>> You write to it and the device does "stuff" to achieve the required
>> effect. Yes this is in proprietary firmware, but from my experience with
>> hardware devices that's not uncommon these days anyway.
> Yes I agree. Even "register" writes to a device are actually an API and
> something in the hardware monitors those registers and does something as a
> result.
>> Let me know if I'm misunderstanding something here. I couldn't see the
>> difference between a register written to via ACPI and one written to via
>> some other protocol (SMBUS? or whatever)
>> Mark
> The reason I'm calling out a distinction here is that "platform" and "device"
> can cover a lot more things. In this case it's an API provided by the platform's
> firmware, not an individual device's firmware. So you can't actually guarantee
> what the platform's firmware did. It could have sent any number of sideband
> commands to devices that it controls. The "platform" could have potentially
> told the GPU to turn up its fans, or lower it's clock as a result of this, but you
> can't possibly know.
> However if we go the GPU example alone, it's a specific single device you're
> controlling. You put the GPU into the characterization that you expected and it
> operates that way.
Got it - fair enough :) Thanks for the explain.

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