On 11-10-16 13:00, Dan Handley wrote:
Materiaalweg 4, NL-5681 RJ Best
Postbus 440, NL-5680 AK Best
Telefoon: +31 (0) 499 33 69 79
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From: Masahiro Yamada [mailto:yamada.masah...@socionext.com]
Sent: 05 October 2016 04:19
Recently I implemented ARM Trusted Firmware BL31 for my SoCs.
But, I am wondering how the boot-flow should be.
I'm no U-Boot expert but as ARM Trusted Firmware (TF) maintainer, I feel I
should say something here.
In general we expect partners to take the bits of TF that work best for them.
So all the bootflows discussed in this thread are valid as far as I'm concerned:
Proprietary Boot ROM -> Proprietary firmware -> TF BL31 -> U-Boot -> Linux
Proprietary Boot ROM -> U-Boot SPL -> TF BL31 -> Full U-Boot -> Linux
TF BL1 -> TF BL2 -> TF BL31 -> U-Boot or UEFI (BL33) -> Linux
Regardless of choice here, it would be nice if all those blobs could be
combined into a single image. Currently the system spends most of its boot
time looking up binaries, and copying them around from device into memory and
then relocate them to a final destination.
The current situation is that I need to create a bunch of tiny flash
partitions: SPL, BL31, U-boot, devicetree, ...
What I WANT to have is just one "boot" partition that holds SPL, BL31 and
u-boot, and then have big u-boot access a filesystem (UBI, FAT or EXT) to
continue from there.
We've gone to some effort to make TF as interoperable as possible with other
boot firmware. If there's more we can do here, please let us know.
As Michal said in an earlier mail, which bootflow you choose depends on what
brings you the most value. Others have stated the advantages of U-Boot SPL over
TF BL2, which I can't disagree with. But there may be other factors to
consider, for example:
* Interoperability with other boot firmware (e.g. UEFI) or other OS.
* Integration with proprietary secure software (which permissively licensed
* Alignment with ARM's Trusted Board Boot Requirements (TBBR) document.
Each vendor needs to make their own decisions here.
Regarding TF BL31, we'd prefer this to remain the EL3 Runtime Software on
AArch64 platforms, because:
* It is the deployment vehicle for ARM support code, which is constantly
evolving (e.g. ARM architectural support, ARM CPU support, errata workarounds,
plus other fundamental IP support).
* It has upstream integration with various Trusted OS.
* It helps standardization by providing reference code for PSCI and potentially
other future industry standards.
There may be other runtime resident firmware present, but we expect these to
execute at a lower EL.
One area that may be worth exploring is whether more can be done to help
integration of the early TF secure world initialization code into other boot
firmware (e.g. proprietary Boot ROMs or U-Boot SPL). This could be useful on
platforms where TF BL1 is not used or TF BL31 is not the first software to
execute on the CPU after reset.
I hope that helps (and is not too controversial!).
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