[Buildroot] Buildroot for Texas Instruments AM65X - add 2nd toolchain?

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

Hello Ryan,

On Thu, 10 Oct 2019 09:32:19 -0500
Ryan Barnett <ryan.barnett@rockwellcollins.com> wrote:

> I'm not sure if anyone has used the AM65X here but the ideal solution
> when using two compiles is to maintain two defconfigs. One for the
> 32-bit Cortex-R5 TI bootloader followed by one that builds everything
> for AArch64.
> 
> There is an issue with compiling using an ARM Cortex-R5 toolchain
> however. Buildroot is setup to build an Embedded Linux System, it only
> supports ARM cores which can run the Linux kernel which the Cortex-R5
> is not. This means a bare-metal toolchain (no C library) must be used
> which buildroot doesn't support. Thus if you want to build the TI
> bootloader package in buildroot using the ARM R5 bare-metal toolchain,
> you will not be able to take advantage of any of the toolchain
> infrastructure.
> 
> With the current state of buildroot, this leads to needing to add your
> own host package for the bare metal toolchain in br2-external which
> would install the toolchain into the host directory. Then you will
> need to add package for the TI bootloader which depend on this host
> toolchain package. The TI bootloader package would take advantage of
> the generic package infrastructure and need to setup and configure the
> TI bootloader source to point to the bare-metal compiler which was
> placed in the host folder.

As I pointed out in my reply, I don't think in this situation you need
two defconfigs, and two separate Buildroot builds.

The bare-metal toolchain can just be a regular Buildroot host package,
and used to build the bare-metal Cortex-R5 code.

See the patch series that I pointed in my reply, which did exactly this
to build the firmware running on a Cortex-M3 co-processor, for a Linux
system running on an Cortex-A53.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com