Re: [PATCH 1/4] riscv: spl: Introduce SPL_OPENSBI_OS_BOOT

[Tom Rini <trini@konsulko.com>]

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On Mon, Dec 12, 2022 at 02:45:10PM +0800, Rick Chen wrote:
> Hi Tom
> 
> > On Fri, Dec 09, 2022 at 08:48:37AM -0500, Sean Anderson wrote:
> > > On 12/7/22 01:23, Rick Chen wrote:
> > > > In RISC-V, it only provide normal mode booting currently.
> > > > To speed up the booting process, here provide SPL_OPENSBI_OS_BOOT
> > > > to achieve this feature which will be call Fast-Boot mode. By
> > >
> > > Can you name this something different. We already have something called
> > > fastboot in-tree (the Android-derived protocol) and there's a Microsoft
> > > technology called fastboot (some kind of hibernation). "OS Boot" isn't
> > > very specific either, since we (almost always) boot an OS. Maybe "Eagle
> > > mode" by analogy to Falcon mode, which lets SPL directly boot an OS.
> > >
> > > (Is this substantially different from falcon mode anyway?)
> >
> > I was kind of wondering if this is different, really, from Falcon Mode.
> > Falcon Mode didn't initially have to factor in other-firmware as that's
> > not a hard requirement on arm32 like it is on arm64 or risc-v.  But my
> > first read of this was that it seems like the RISC-V specific side of
> > doing Falcon Mode and dealing with the prior stage needs correctly.
> >
> 
> Yes. It is a little bit different from the Falcon mode (SPL_OS_BOOT=y).
> When I try to enable SPL_OS_BOOT, it will encounter that SYS_SPL_ARGS_ADDR and
>  jump_to_image_linux() shall be defined but they are un-necessary for RISC-V.
> Because the flow of OpenSBI and SPL_OS_BOOT are totally different code
> flow in board_init_r() of common/spl/spl.c.
> That is why I added a new symbol called SPL_OPENSBI_OS_BOOT for this
> RISC-V fast boot implementation.

Those sound like fairly minor challenges for the same fundamental
concept. We have SYS_SPL_ARGS_ADDR for "where is the device tree to
pass along". We might need to do a little code re-factoring here. But
maybe also a little bit of explaining why we wouldn't be booting to the
OS directly but instead passing back to openSBI to do this? That's not
normally how RISC-V boots the OS, right? Or am I miss-understanding
something here?

-- 
Tom

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