Hi Nico,
On 15.12.2021 12:21, Nico Huber wrote:
Hi Krystian,
On 14.12.21 13:00, Krystian Hebel wrote:
For our work on POWER9 coreboot port we were using Skiboot [1] packed into
FIT payload.
I might just miss it because I never worked with FIT, but maybe I'm not
the only one: Can you elaborate why you chose FIT? Reading through your
mail (and without further knowledge) it would just seem like the wrong
choice.
Good point, I spent so much time in this project that I treat too many
things as obvious. Don't hesitate to ask if I omit something important.
Skiboot must be supplied with information about hardware. Some of that
is generated by code based on current configuration (e.g. number of
cores, their IDs, memory amount and associativity), but a lot is always
the same for a given platform or even whole architecture (BMC sensors,
interrupt controller, register address space, LPC controller). This can
be passed either in HDAT structure (Hostboot data, proprietary and
mostly undocumented format in supposedly open firmware) or, as we
learned after asking on OpenPower-Firmware mailing list, using FDT:
https://lists.ozlabs.org/pipermail/openpower-firmware/2021-May/000641.html
In our current setup that second, constant part is supplied as FDT in
FIT image so it can be added as .dts file, which is easier to read and
understand than C code that would be used for creating these nodes.
Note that this doesn't apply to QEMU port that is currently under
review on gerrit. In that case FDT is created by QEMU and its address
is passed in one of the registers; this is not the case on hardware
platform where it has to be created either from scratch or, as in our
case, from preexisting skeleton.
--
Krystian Hebel
Firmware Engineer
https://3mdeb.com | @3mdeb_com
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