Monday, March 16, 2015

Is max_brigthness coming from a random number generator?

First off, thank you for sending contributions to Lantern. Please keep them coming, we really need more data for meaningful statistics.

Now for the main dish: I wonder what's the cause of the seemingly random values of /sys/class/backlight/*/max_brightness as seen in the wild.

Currently I have instances of each of those:

[7, 10, 15, 89, 100, 255, 312, 494, 825, 852, 937, 976, 1808, 2632, 3828, 4437, 4438, 4882]

So one laptop has 7 steps of backlight intensity, another has 312, 976 and some have 4882. What is the cause of such a wide range of values? Can the hardware be the cause? But then again, are engineers that built this really so careful to expose, say 852 values instead of 825, or 100.

Given how most backlight control from user's point of view works, apart from smooth transitions that some Windows 8 laptops do, 25 would be way more than enough values.

If anyone has some input on what may be causing this, I'd love to hear that. I'll start working on improving the analysis script to do some correlation between the CPU type, GPU type and observed values.