[Letux-kernel] 25% speed upgrade for some GTA04!

H. Nikolaus Schaller hns at goldelico.com
Sat Oct 12 13:52:08 CEST 2019

I am happy to announce that we have developed code that
(re)enables the 1GHz clock frequency of the DM3730CBP100
that is installed in ca. 50% of the GTA04 devices.

This allows to get 25% more processing speed since
it currently was limited to 800MHz.

The trick was to define additional "OPP" (operation points)
for DFVS (dynamic frequency and voltage scaling).

It was not available for the DM3730 processor because of
three reasons, where we had to work out solutions:

1. not all DM3730 chips are capable of running at 1GHz.
   Therefore the mainline kernel uses only 800MHz as the
   least common available limit.
   But there is a register inside the DM3730 where Texas
   Instruments has stored if the individual chip can run
   at 1 GHz. So we had to read this bit and disable/enable
   the OPP1G.

2. DM3730 has an internal voltage regulator for the
   "Body Bias" which is called ABB. This must be switched
   to a different mode for 1GHz operation. The driver
   for this regulator was already available, it just
   was not controlled.

3. 1GHz operation may drive the DM3730 very hot. So
   to protect the chip from overheating and being
   damaged, we had to add thermal management. The
   drivers were already available and in place and
   operation for OMAP4 & OMAP5 (Pyra Handheld). So
   we just had to copy and adapt the definitions.
   We now reduce clock rate if the chip reaches 90°C
   Junction Temperature. This usually happens only
   for a short moment (<1 second). And as long as
   you don't run resource intensive software, it
   won't be noticeable.

Our work has now been accepted by kernel maintainers
and appeared in linux-next. It likely will become part
of Linux v5.5. But you do not have to wait since we
already have it in letux-5.3 and letux-5.4-rc.

I hope you enjoy that we still support an 8 years old
device. Where else do you get a speed improvement
of 25% after that time?

Please let the world know about this :)

And of course, dig out your GTA04 and update to the
latest software.

BR and thanks,

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