Re: [External] RE: [RFC] Documentation: Add documentation for new performance_profile sysfs class
From: Mark Pearson
Date: Mon Oct 05 2020 - 13:47:04 EST
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.
Thanks
Mark