Openness of the RPi (Was:Pre-order your UBUNTU EDGE)

[Scott Sullivan]

On 07/26/2013 12:42 PM, Christopher Browne wrote:
> I concur with Scott.
>
> Yep, not yet properly a product, fair chance of failure.
>
> And "success" has a pretty high chance of substantial compromise,
> notably with proprietary video or radio drivers.  That's the place where
> Raspberry Pi has an arguable significant failing.

That's where it get's funky with the RPi. At the start there where some 
drivers in the kernel tree that were proprietary. Those got sorted out 
and released. It's how we now have OSes like Plan9 on the RPi.

What remains is two major things.

1) The Boot Firmware

This is because the RPi doesn't have a conventional boot vector. Instead 
the GPU boots first (and it's actually 90-95% of the SoC die) and loads 
it's firmware from a specific file in a FAT partition on the SC. It then 
loads the kernel into the ARM core and starts it.

2) The GPU Firmware

The biggest hoopla around this was that the GPU kernel driver was not 
what people we're expecting. Most GPU drivers manipulate the registars 
and hardware directly. This is not the case with the RPi. Instead the 
GPU is running as an independent Co-Processor with it's own OS 
(Firmware). It then exports a direct OpenGL ES api to the ARM and so the 
kernel driver is only message passing code to get the OpenGL command 
stream across. We don't have hardware access to the GPU.

So while technically the RPi has fully open sourced all it's kernel 
drivers, we're still locked out of 95% of the most interesting hardware 
because of proprietary firmware. This is where FSF guidelines about open 
hardware start to make sense.

It also means we're at the vendors mercy for OpenCL or other GPGPU 
technologies because we can't implement without reverse engineering the GPU.

There has been significant progress on that front though. This is Good 
Article on the state of reverse engineering various ARM SoC GPUs.

http://blog.emmanueldeloget.com/index.php?post/2013/03/08/The-SoC-GPU-driver-interview

Wayback snapshot as it's down at the moment:

http://web.archive.org/web/20130624012049/http://blog.emmanueldeloget.com/index.php?post/2013/03/08/The-SoC-GPU-driver-interview

-- 
Scott Sullivan
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