Re: Pi4 to Pi5 migration

Computer Nerd Kev <not@telling.you.invalid> wrote:

bp@www.zefox.net wrote:

Computer Nerd Kev <not@telling.you.invalid> wrote:

No the code running on the GPU is all written by Broadcom and Linux
software just talks to that, so nothing needs to be compiled for
the GPU in order to use functionality that's in the stock GPU
firmware. The bottleneck at this point seems to be mainly
application developers adding support for the APIs, but this isn't
an issue with compilers, just the usual limits of time, money, and
willpower.

 
Ok, that clarifies things considerably. Is the API public, at least?
Then folks could experiment.

 
Broadcom's API is DispmanX, which some programs have used directly,
but libbrcmEGL is their library that presents an OpenGL interface
and is thus easier to adapt software to. Separately the Linux
kernel now has its own drivers, which are used via Mesa. I'm not
sure how the performance compares, but the Mesa drivers are the
popular ones these days.

At the risk of correcting myself about details that nobody cares
about anyway, it turns out the original work on Mesa's VC4 driver
was led by a Broadcom developer as well. So that would really be
Broadcom's current graphics API. Seems it actually bypasses the
original closed-source firmware running on the VPU, to do that
graphics processing on the CPU instead, which is a bit of a waste
of the GPU's processing abilities. But it seems they preferred that
to opening the sources and build system for the VPU firmware and
improving upon that, though that's still used for hardware
management tasks.

Here's the VC4 driver developer's blog:
https://anholt.livejournal.com/

And their post about being hired by Broadcom to write the GPU
driver for Mesa and the Linux kernel:
https://anholt.livejournal.com/44239.html

More recently the GPU drivers for the RPi4 and 5 have be developed
by Igalia, presumably as sub-contractor for Broadcom since Igalia
took over from the Broadcom developer:
https://www.raspberrypi.com/news/vc4-and-v3d-opengl-drivers-for-raspberry-pi-an-update/
https://www.igalia.com/2023/09/28/Raspberry-Pi-5-Announced.html
https://www.igalia.com/technology/graphics

It's interesting to find out where all this code comes from.
Broadcom have been more involved than I thought.

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