Re: Raspberry PI information

Hello, and happy solstice!

> I'm a long-time NetBSD user and developer, and have run NetBSD on
> various hardware (alpha, i386, amd64, sparc, sparc64, macppc...).
> I also run qemu-based arm and aarch64 systems, but have so far
> not had my hands on actual arm hardware.  Raspberry PI is as far
> as I understand fairly "mainstream", so I'm looking at
>
> https://wiki.netbsd.org/ports/evbarm/raspberry_pi/
>
> and I'm trying to figure out what works and what doesn't, and how
> one operates such systems.  Am I the only one who comes out of
> this with waay too many un-answered questions than expected?
> Who's willing to work with me to improve this?  Some examples:

The ARM ecosystem is large, and NetBSD supports many, many boards. It may 
come as no surprise to learn there are several ways to do many things, and 
the reasons to choose one over another aren't always clear or easy to 
discover.

It'd be nice to have as much of this information in one place as possible.

I'll try to answer what I can :)


> 1: status of RPI5 support:
>  As of early 2024, NetBSD does not support the Raspberry Pi 5.
> but later under "NetBSD current" (unspecified version):
>  RPI5 general support (UEFI firmware required)
> so which is it?

I got one, and NetBSD under UEFI runs on it, but the last time I checked 
(October, I think), ethernet didn't work and NetBSD can't change the 
processor frequency, so it needs to be set in the UEFI menus. I don't 
remember the status of wifi / Bluetooth.

>  RPI4 general support (UEFI firmware required)
>  RPI5 general support (UEFI firmware required)
> There is a separate section named
>  UEFI booting
>
> but it is IMHO short on concrete details for how to go about
> using it.

This could be improved, for sure. Other systems, like the Orange Pi 5, 
work surprisingly well with UEFI, much better than with native booting.

> Later under "RPI4 xhci" is mentioned
>  One workaround is to switch to UEFI, but that leads to a 3GB
>  memory limit and needing a monitor.

Neither of those are true (any more?) I've been running an 8 gig RPi 4 via 
a serial console for years now.

> 5: SD card structure and booting process
>
> This section finishes off with a non-clickable URL to
> https://www.raspberrypi.org/documentation/configuration/config-txt/boot.md
> which redirects to
> https://www.raspberrypi.com/documentation/computers/configuration.html
> and which starts by talking about raspi-config.  Is that program
> even available on NetBSD?

No, it isn't. In the past, most documentation had information about making 
changes to config.txt and cmdline.txt, but more recent documentation 
suggests raspi-config without explaining the actual changes.

> 6: Ability to boot from other media?
>
> I've understood that microSD cards are the easiest way to boot a
> raspberry pi, but that they wear out rather quickly.  How does
> one use e.g. an eMMC card instead?  Without going the route via
> first installing Linux?  What about these newfangled nVME HATs
> available for use with the RPI5?

The Pis 3A+, 3B and 3B+ have one-time programmable memory to enable USB 
booting. The Pi Zero 2 has it too, but already enables USB booting, 
apparently.

The Pis 4 and 5 have EEPROM and can be set to USB booting.

Personally, I've not bothered and just have a small microSD card on all 
systems and use the "root=" line in cmdline.txt to root elsewhere. The 
kernel also lives on the microSD.

> ends with
>   \todo Explain if updating firmware is necessary when e.g.
>   moving from 8 to 9, or 9 to current.
> "current" here probably refers to pre-10, no?  Could perhaps be
> updated with more current information?

We should also clarify which Pis load netbsd.img, netbsd7.img, along with 
config.txt changes for kernel name, 64 bit, et cetera.


> 9: RPI4 UEFI 3 GB
>   To work around bugs in hardware (that may or may not be fixed
>   in recent RPI4) and because not all OSes have workarounds, the
>   UEFI firmware's default is to limit RAM to 3GB. NetBSD 10 can
>   be used with more, so this needs to be configured in UEFI.
> How?

The UEFI pre-boot menus allow you to set the amount of memory the OS will 
use.

> 11: Updating the firmware
>   It is somewhat likely that running NetBSD from a given branch
>   X with firmware from a branch Y < X will not go well. It is
>   unclear if firmware from a branch Y > X will work. It is
>   standard practice to use firmware from the right branch. An
>   alternative view is that newer firmware is usually better, and
>   the the firmware needs to be new enough for the hardware.

> The first sentence is kind of scary.  However, this does not say
> where the firmware (is supposed to) come from.  Is it maintained
> inside the NetBSD source tree as a binary blob (it sounds like
> it)?  I suppose it originally comes from elsewhere?  Where, both
> in-tree and elsewhere?

This is puzzling to me. First, these are boot files. "Firmware" usually 
has the connotation of something firm, like a flash chip. Second, it has 
been years since the boot files have been meaningfully out of sync with 
NetBSD's expectations, unless there are things I haven't seen yet.

For the most part, AFAIK, you can safely just fetch the latest boot files 
from here and expect them to Just Work:

https://github.com/raspberrypi/firmware/releases

> Always referring to the "upstream" documentation gives the task
> of distringuishing betwen "system-dependent" and "Linux-
> dependent" parts of the documentation, and then finding out how
> to do the corresponding task in NetBSD is left as a task for the
> user to figure out.

Yes, this makes it hard for me even though I've been using Raspberry Pis 
of every kind since they came out. I can only wonder at what a beginner 
would make of it.

> Sorry for this being a bit negative; I'm willing to work with
> whoever is able to provide me with accurate information in this
> area.

It's not negative, in my opinion, to express a bit of exasperation now and 
then, particularly when it's in the interest of doing something 
constructive :)

I'm happy to help however I can. I've collected lots of notes over the 
years - perhaps I should go through them and see what can be used in 
NetBSD's documentation.

John