[Tinkerphones] GTA04: TV-out working again!

Paul Boddie paul at boddie.org.uk
Sun Jun 3 17:15:56 CEST 2018

On Friday 1. June 2018 23.04.43 H. Nikolaus Schaller wrote:
> Hi,
> although there seems to be not much activity here, there is still progress
> with the Letux OS / GTA04 code base. It is neither forgotten nor abandoned
> :)

I feel a bit bad for neglecting the MIPS-based side of the Letux kernel 
effort, but I think that for technical and practical reasons it had to take a 
back seat for me personally, and as you know, my focus has been on 
microkernel-based stuff instead.

However, there is something of an intersection between the above and the 
actual topic of this thread...

> I have finally made the TV-out of the GTA04 work again. It did already work
> long time ago (I think in 3.12 kernel), but after upgrades to Device Tree
> we were not able to catch up with upstream changes and understand them.
> And to be honest, TV-out was not on highest priority.

So, one forum I look at occasionally is related to portable gaming, 
specifically Dingoo and GCW-Zero, and there's an ongoing thread there:


It seems that even on small devices with their own displays, there is interest 
in external displays. It is also a coincidence that I was reading about Neo900 
capabilities for this only recently, too.

One of my many tasks with the microkernel-based stuff will be to look into 
getting HDMI output working with the MIPS Creator CI20, which Linux already 
supports, but which would need a bit of effort to do in a different way, 
although hopefully not much more than initialising the hardware.

> But now I spent some hours and made it working again. Mainly there were
> typos in the DT sources we had tried before. E.g.:
> >>> &control_devconf1 {
> >>> 
> >>> 	pinctrl-name = "default";
> > 
> > ^^^ here is the bug: this property must be called "pinctrl-names".
> And after finally recognizing that the video cable was broken overnight
> (it was still working yesterday) and adding some "ti,invert-polarity;" the
> TVout of the GTA04 works again :)

I think that device tree sacrifices reliability for flexibility, which is 
amusing (albeit not after a long debugging session, I'm sure) given that it 
comes from a community who have probably derided dynamic languages and things 
like XML. Maybe there needs to be a tool to validate device tree resources.

> Quality isn't bad - so switching to a desktop mode (and taking care of
> portrait vs. landscape dimensions) is just a matter of easy-to-use
> user-space software...
> So by connecting to a projector or monitor and adding a keyboard through
> USB-OTG or Bluetooth you can easily convert your smart-phone into a desktop
> PC with standard Debian inside...

I think it is a great selling point for open hardware. I know that there are 
proprietary products which offer this, but it is probably a reason for them to 
elevate the price and restrict the availability.

Congratulations on figuring out the problem!


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