[U-Boot] [PATCH 1/3] rockchip: rk3399: add tpl support

[Heiko Stübner]

Am Donnerstag, 18. April 2019, 08:35:49 CEST schrieb Philipp Tomsich:
> Simon,
> 
> > On 18.04.2019, at 06:32, Simon Glass <sjg at chromium.org> wrote:
> > 
> > Hi Kever,
> > 
> > On Mon, 1 Apr 2019 at 02:21, Kever Yang <kever.yang at rock-chips.com> wrote:
> >> 
> >> Rockchip platform suppose to use TPL(run in SRAM) as dram init and
> >> SPL(run in DDR SDRAM) as pre-loader, so that the SPL would not be
> >> limited by SRAM size.
> >> This patch add rk3399-board-tpl.c and its common configs.
> > 
> > So this means that TPL inits SDRAM? That seems strange to me...why
> > have SPL at all, then? What is SPL supported to do on RK3399
> > platforms?
> 
> For TPL->SPL implementation on Rockchip, we generally rely on the BootROM
> to load the TPL stage (to SRAM) and the SPL stage (to the start of DRAM).  The
> BootROM usually limits the size of the SPL stage, so we can’t use a full U-Boot
> already.
> 
> Even more constricting are the TPL size constraints (as this seems to have originally
> only been intended to be size-optimized DRAM init code) on some devices.

and maybe for a broader functionality description, something needs to
load things like ATF via a FIT image from a mmc for example.
(which needs FIT code and also real mmc drivers).

And as we experienced on rk3288 as well recently, SRAM may be very well
too small to accomplish that, so TPL needs to init the sdram separately
to make room for the code needed to get ATF up and running, which must
be done before jumping into proper uboot.

Heiko