Re: Xen on RP4

[Ash Wilding <ash.j.wilding@gmail.com>]

Hi,


>> I think the best compromise is still to use an ACPI string to detect
>> the platform. For instance, would it be possible to use the OEMID
>> fields in RSDT, XSDT, FADT?  Possibly even a combination of them?
>>
>> Another option might be to get the platform name from UEFI somehow. 
>
> I included appropriate strings in e-mail.  Suitable strings do appear
> in `dmesg`.


Just as a heads-up, SMCCC does define the optional SMCCC_ARCH_SOC_ID [1]
function and this is listed as mandatory in the Server Base Boot Reqs
(SBBR); see pp 15 of ARM DEN 0044F [2].

Unfortunately it looks like RPi 4's firmware doesn't currently support
this, or at least the rpi4-uefi project [3] didn't think so as of FW
version 1.6 [4], but I couldn't find equivalent SBBR feature tracking
pages on that site for FW versions 1.7 or 1.8 to confirm, nor could I
find any reference to SMCCC_ARCH_SOC_ID in the RPi 4 FW sources [5].

On the bright side, while not very helpful in the short-term, note that
Arm's recently announced SystemReady [6] program is an evolution of
ServerReady (SBSA+SBBR) but for other segments and applications incl.
Embedded, IoT, and general Linux Boot.

That means in future we should see more platform firmware supporting
SMCCC_ARCH_SOC_ID, as the SiPs will (hopefully) want their platforms to
be SystemReady certified.

Hope that's useful info.

Thanks,
Ash.

[1] https://developer.arm.com/documentation/den0028/c
[2] https://developer.arm.com/documentation/den0044/latest
[3] https://rpi4-uefi.dev/about/
[4] https://rpi4-uefi.dev/status-v1-6-firmware/
[5] https://github.com/pftf/RPi4/tree/master
[6] https://developer.arm.com/architectures/system-architectures/arm-systemready