Thanks Ahmad for reaching out!
There is a PR [1] on the Firmware Handoff specification that is still under discussion. Could you take a look and see if it could accommodate your use case?
To confirm my understanding, would the desired flow be something like:
1. BL31 passes a read-only DT to OP-TEE via the Transfer List (TL) 2. OP-TEE consumes the DT, adds memory reservations via a DTO, and appends this DTO to the TL 3. BL31 then forwards the updated TL to BL33
Does that match what you had in mind?
[1]: https://github.com/FirmwareHandoff/firmware_handoff/pull/74
________________________________ From: Ahmad Fatoum a.fatoum@pengutronix.de Sent: 11 June 2025 19:09 To: Manish Pandey2 Manish.Pandey2@arm.com Cc: op-tee@lists.trustedfirmware.org op-tee@lists.trustedfirmware.org; BAREBOX barebox@lists.infradead.org; rouven.czerwinski@linaro.org rouven.czerwinski@linaro.org; Michael Tretter m.tretter@pengutronix.de; kernel@pengutronix.de kernel@pengutronix.de Subject: Firmware Handoff for DT Overlay created by OP-TEE?
Hello Manish,
In your recent talk[1] at LinaroConnect about the Firmware Handoff specification, you were asking about what other use cases it could address for OP-TEE.
We ran into a possible use case that we would like to share:
BL2 can pass a DT to OP-TEE, which it would use to discover memory and to fix up with memory reservations covering the memory it carves out for itself.
OP-TEE also supports passing along the reservations as a device tree overlay. AFAICS, there is no way currently to have both: A DT for OP-TEE to probe hardware from and a way to pass the normal world a device tree overlay in return.
I think this could be neatly addressed with Firmware Handoff and would be a motivation for us to implement support in barebox BL2/BL33 to take advantage of this. The current way is suboptimal as we would prefer the DT passed to OP-TEE to be read-only. This avoids either having to copy it or to pad it sufficiently in anticipation of it growing with the addition of the new nodes.
[1]: https://www.youtube.com/watch?v=RxU798h8aiE
Cheers, Ahmad
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