[Buildroot] [PATCH v2-RESEND 3/6] zynqmp-pmufw-binaries: new package

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello Luca,

On Wed, 11 Apr 2018 23:03:17 +0200, Luca Ceresoli wrote:

> > So this hints at the fact that this firmware is board specific. Is that
> > correct ? If so, shouldn't we plan on making the Git repo and its
> > version configurable ?  
> 
> The firmware is board-specific and configuration-specific. The plan for
> that repo, however, is to have all supported board+config combinations
> supported in all versions, thus the lack of a version selection knob.

"all" ? I'm pretty sure a lot of people will be doing custom designs,
and will not be willing to push their firmware binary to your public
repository.

> > I mean, what are the chances that for some random ZynqMP board, your
> > Github repo will contain the appropriate firmware file ?  
> 
> Good point. My repo there is ready to hold any possible board+config
> combination that is interesting for known boards. I would love to host
> more boards there (contributilns would be welcome). However I don't
> think we'll ever see any custom board, which reduces its usefulness.
> 
> Thus a simpler, but more flexible, option might be to nuke the
> zynqmp-pmufw-binaries BR package and let uboot fetch the pmufw.bin from
> a plain URL (https:// or file://). For standard devboards the URL could
> point to my repo, but it can be anywhere else (for custom boards).

Ah, this seems like a better option indeed, especially since the
firmware is a single file. It could be locally available, or downloaded
from HTTP. Sounds like a good plan.

> > Generally speaking, it's a bit annoying that we can't build this from
> > source. I understand it needs a Microblaze toolchain, so it's very
> > difficult to integrate in Buildroot :-/  
> 
> Indeed, and this is *the* big topic.
> 
> There are several variations that could be considered, but none have
> been attempted AFAIK. Here they are, simplest to hardest:
> 
> 1. Build the PMUFW in Buildroot (kind of)
> 
> Add a script (e.g. board/zynqmp/build-pmufw.sh) that builds a microblaze
> toolchain and the PMUFW with a given config. The commands are already
> there: [0].
> 
> The script would then be called manually before Buildroot runs, or it
> could be wrapped in a Buildroot package that uboot depends on. Takes ~8
> minutes on a modern quad core machine.
> 
> * Simple to do, not well integrated, longer build time.

Yeah, the integration with Buildroot here is really not great, because
Crosstool-NG will do its own downloading, etc.

> 2. Let SPL install the PMUFW config
> 
> This is what the Xilinx workflow does (in the Xilinx FSBL, which is more
> or less equivalent to U-Boot SPL). This allows The PMUFW can be a unique
> blob for all boards.
> 
> This moves the configuration object from a piece of early firmware
> (PMUFW) to another piece of early firmware (SPL). Both pieces are
> residing in the same BOOT.BIN file, so there's no added flexibility for
> the "user": upon a config change, you still have to update the BOOT.BIN
> file in the boot medium.
> 
> There are also licensing issues preventing this, since the configuration
> object file license is not compatible with the U-Boot license. Xilinx
> _might_ be willing to fix this, however.
> 
> * Could be doable, perhaps tricky.
> 
> 3. Don't have any config object...
> 
> ...and change the PMUFW source code to assign dynamically peripherals to
> cores at runtime, based on requests from cores! :->
> 
> * Maybe doable, potentially dangerous, definitely hard to do.

Not sure I understand enough of what the PMUFW is doing to understand
(2) and (3). And yes, I did attend your talk at FOSDEM about
ZynqMP ! :-)

> Any idea or suggestion is very welcome, although I think we cannot do
> much more than looking for the least evil solution...

I think for now the solution you propose to add an option in U-Boot to
indicate the path/URL to the PMUFW binary is the easiest one. It can
always be improved later if better solutions emerge.

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com