For most of the past 20 years, brightness control has been ring 0 mechanism, ring 3 policy. ACPI provides a mechanism for the OS to interface with the EC in a w

For most of the past 20 years, brightness control has been ring 0 mechanism, ring 3 policy. ACPI provides a mechanism for the OS to interface with the EC in a way that aligns with any SMM that's going on, and where we are now is just fundamentally better than the halcyon DOS days you're pining for. It also means we don't need to involve another computer in here, which is what the EC is. > Otherwise the EC takes care of everything. See, that's just not possible. Modern displays have the backlight integrated into them, and the control is over something that's roughly i2c over eDP. But the same i2c channel needs to be accessible to the OS, and if the OS and the EC try to access that at the same time then things will break. So you need some kind of locking, and that's utterly impossible if hitting a key just jams you into SMM and smashes some bits over there - you might do that in the period between the OS writing an index and writing a value. > ...and if it was handled by SMM, Windows doesn't need to care at all! The behaviour of the SMM handler is defined by the platform vendor, and if the vendor ends up only testing against one OS then they may embody assumptions about that OS. In this case they assumed that SMM could only be triggered when running on CPU 0, which was true in the case of Windows and not in the case of Linux. This isn't about Windows needing to care, it's about SMM being a mechanism for vendors to accidentally assume that what Windows does is universal. > Then again, I'm not surprised at your misdirection and half-truths given you've been essentially shilling Treacherous Computing and Restricted Boot among other hostilities. I am arguing that it is better that this code lives in visible space, executed in the context of the OS, and subject to security boundaries that the OS imposes. You appear to be arguing for opaque code running on a separate microcontroller, mediated by code running on the main CPU, but which stops the entire OS from running while it executes, and which is hidden from the OS. Which of these sounds better for the user?