[U-Boot-Custodians] SPL / TPL

[Bin Meng]

Hi Masahiro,

On Wed, Oct 9, 2019 at 12:50 AM Masahiro Yamada
<yamada.masahiro at socionext.com> wrote:
>
> Hi Bin,
>
>
> On Wed, Oct 9, 2019 at 12:31 AM Bin Meng <bmeng.cn at gmail.com> wrote:
> >
> > Hi,
> >
> > Simon is on vacation, hence I hoped to get the clarification from
> > other maintainers.
> >
> > As I see in U-Boot currently only NXP PowerPC uses TPL in the NAND
> > configurations, and some ARM boards use TPL.
> >
> > It looks in x86 we are using TPL in a different boot flow and this
> > confused me a lot in the past.
> > In x86 we expect TPL to load SPL then U-Boot proper. (TPL => SPL =>
> > U-Boot proper)
> >
> > However in README.TPL, it says TPL is the 3rd program loader, to be
> > loaded by SPL. So if my read is correct, the expected boot flow is SPL
> > => TPL => U-Boot proper.
> >
> > I believe only one boot flow is the correct way. So which one is correct?
>
>
>
> When the TPL support was first developed,
> it worked as  SPL -> TPL -> U-Boot proper.
>
> SPL is a short of Secondary Program Loader,
> and TPL was Tertiary Program Loader.
>
> For the platforms using this 3 stage bootstrap,
> its SPL is really small (and implemented in a rather ad-hoc way)
> and its TPL tends to be as large as the SPL of other non-TPL platforms.
>
> I noticed some problems in the SPL framework
> because TPL corresponds to SPL of the 2-stage-boot platforms.
>
> As a result, we end up with duplicating SPL configuraion
> like CONFIG_SPL_FOO, CONFIG_SPL_BAR,
> to CONFIG_TPL_FOO, CONFIG_TPL_BAR.
>

Thank you very much for the information. This clears my confusion.

>
> I pointed out TPL -> SPL -> U-Boot proper
> would make more sense.
>
> TPL (let's say Tiny Program Loader) is a really small
> implementation for that platform,
> and SPL can re-use the common SPL framework.

I think you wanted to say "TPL can re-use the common SPL framework"?

>
> This requires flipping the boot order.
>
> I do not know how much consensus we got,
> or documented somewhere, though.
>

It looks to me that we never get in agreement as we have the document
README.TPL describes one boot flow and some other platforms implement
another way.

Regards,
Bin