I noticed there were frequency settings above 1209 MHz defined there. The highest one, DVFS_F0_0 goes above 1.7 GHz.
The code that seems to define the maximum frequency starts on line 1573 of that file. It relies on the returned value of PTP_get_ptp_level to define it. Since PTP_get_ptp_level is just a external header on that file, I needed to search the git repo to find its definition. Turns out it is in this file mt_ptp.c. Pay special attention to line 1018 and below: https://github.com/varunchitre15/MT6...mt_ptp.c#L1018
There's this interesting bit:
#if defined(MTK_FORCE_CPU_89T) return 3; // 1.5GHz #else
I think I read the 6589T also has a higher GPU clock, and it can handle 2 GB of RAM with no problems. I'm not saying that the difference between the 6589 and the 6589T is just a kernel config, in fact, the chip most likely got a new revision. This source code leaked before there was any talk of a turbo revision of the 6589, so I think it's safe to assume that on newer code trees there may be fixes for the 2 GB of RAM and a higher GPU clock.
But I wonder, if the 6589 (not T) is able to go up to 1.5 GHz or even 1.7 GHz. It would be good if someone could compile that kernel with some modifications to make it think it will be running on a 6589T (adding a #define MTK_FORCE_CPU_89T should be enough) and see if it works fine. Since that source code came from a Acer model, maybe it would be easier to start tests on that device (because we can be sure the source is 100% compatible). I think it may run, but it may heat a lot or it may drive the voltage of the CPU up to a point where the phone's PCB is not prepared to deliver, causing damage (maybe the T revision chip fixes this).