[Lenny400] [Mipsbook-devel] jz4740.dtsi (JZ4730 DT upstream)

Paul Boddie paul at boddie.org.uk
Mon Jun 29 23:52:39 CEST 2015

On Sunday 28. June 2015 19.35.12 Dr. H. Nikolaus Schaller wrote:
> Hi all,
> Am 28.06.2015 um 12:21 schrieb Dr. H. Nikolaus Schaller <hns at goldelico.com>:
> > Today is a good day for the MiniPC / jz4730 based devices :)
> > 
> > Linus has merged the jz4740.dtsi
> > 
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?i
> > d=78c10e556ed904d5bfbd71e9cadd8ce8f25d6982
> > 
> > into linus/master.
> > 
> > So the infrastructure for writing a jz4730.dtsi and adapting drivers
> > where needed is here.
> I have plugged together sort of a sketch:
> http://git.goldelico.com/?p=gta04-

Thanks for keeping an interest in this!

> Here some notes for observations:
> * the base is our h=refs/heads/4.2-rc1 tree which includes merge of the
> above mentioned tree (differences to linus/master are in ARM OMAP and
> additional device drivers)
> * this code compiles but IS COMPLETELY UNTESTED
> * the device is called “minibook”
> * use letux_defconfig - because that is the name of our Linux distribution
> (and in the long run should support different devices)
> * the kernel still identifies itself as 4.1.0 - because Linus has not yet
> officially released 4.2-rc1
> * the device tree is automatically compiled into the uImage (by the Makefile
> coming from upstream - so I have not changed the build system, just added a
> minibook.dts)

My recent "bare metal" experiments failed to work whatsoever on the Letux, but 
it was still happy booting a Linux 2.6 kernel from MMC, and I ran out of 
patience trying to debug the "undebuggable". I later got some hints about 
reset operations from someone with more knowledge about the JZ-series, but I 
then got stuck trying to do something with the Ben NanoNote that also didn't 
work out (related to interrupts and an initial error condition that I can't 
manage to figure out, even though Linux must obviously be able to).

So any boot-level wisdom would be especially appreciated. As I noted earlier, 
the U-Boot and Linux patches are quite horrible, and I still strive to find 
the simplest recipe possible to boot these devices so that a more thorough 
understanding can be attained.

> * Daniel’s PM MCU driver does not compile (some structs have changed) and
> needs to be fixed (therefore #CONFIG_POWER_MINIPC is not set)
> * the device tree is prepared to add an &i2c node but I have not yet seen
> any driver (not for jz4740, jz4780)
> * there is no jz4730 specific code or DT config - everything is copied or
> taken from jz4740 (which is likely wrong)
> * things like gpios, keyboard scanner, lcd, usb, RAM/flash memory have to be
> worked on

From what I can see from the code that supposedly works on the jz4730, the LCD 
initialisation is practically the same as for the jz4740. Various registers 
are initialised and then the SoC assumes the job of continuously reading from 
RAM and streaming the pixel data to the display. The difference between the 
Letux and the NanoNote is that the latter uses a "narrower" connection and has 
an SPI command link to the display.

A lot of the other things should be rather similar, but as I recall from my 
previous (futile?) efforts, the locations of registers may be slightly 
different, and it seemed at the time that some methods of access were 
different, too. That might have been specific to the GPIO configuration 
registers, however.

> Comments, fixes, patches, ideas hints, criticism welcome :)
> And if you want to test: beware! It may brick the device. And it probably
> needs access to a serial console to see what is going on. I have to find
> my Letux 400 with such interface first and check if it still works.

A long time ago it seemed like you might have found a way of unbricking these 
devices, so it would be good news if you managed to rediscover some of that 
wisdom. ;-)


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