[U-Boot] [RFC] ARM: rmobile: create DT memory nodes for R8A7795 3.0 and newer

[Eugeniu Rosca]

Hi Marek, All,

I am looking forward for the solution/approach you are going to reach
in this thread.
Currently, integrating Renesas Yocto v3.7.0 release [1], I can see
that the increase of SoC/SiP versions supported in this release
increases the number of ATF/U-boot build variants dramatically.

Renesas U-boot starts to rely not only on defconfig, but also on
build-time flags passed via Yocto recipes (see usage of
get_uboot_config_opt in [2,3]). This doesn't look right (I don't see
U-Boot KCFLAGS being adjusted too often in mainline). Latest Renesas
ATF also adds a bunch of new make flags, all being related to SiP DRAM
configuration, which means it's very easy to pick the wrong setting at
build-time and then deal with obscure issues afterwards (hopefully the
target just doesn't boot) :(

FWIW, with regard to FDT support in ATF, it seems to be there starting
with commit [4] and there are already users/callers of libfdt APIs in
the tree [5].
Something I am wondering about is why not getting the memory
configuration in ATF at runtime? Haven't DRAM vendors thought this
information (number/size of DDR banks) would be useful and should be
exposed by HW and accessible by SW? Currently Renesas tells their
customers that the correct SiP-specific DDR configuration has to be
hardcoded during build process. If anybody has an explanation why
runtime DDR detection is not possible in ATF, could you please share?

Best regards,
Eugeniu.

[1] https://github.com/renesas-rcar/meta-renesas/releases/tag/Renesas-Yocto-v3.7.0
[2] https://github.com/renesas-rcar/meta-renesas/blob/Renesas-Yocto-v3.7.0/meta-rcar-gen3/include/uboot-control.inc
[3] https://github.com/renesas-rcar/meta-renesas/blob/Renesas-Yocto-v3.7.0/meta-rcar-gen3/recipes-bsp/u-boot/u-boot_2015.04.bb
[4] https://github.com/ARM-software/arm-trusted-firmware/commit/91176bc6363d
("Import libfdt v1.4.1")
[5] git grep -El "fdt_|fdtw_" -- ":\!*lib/libfdt/*" "*.c"
common/fdt_wrappers.c
plat/arm/common/arm_dyn_cfg_helpers.c
plat/arm/css/sgi/sgi_image_load.c
plat/qemu/dt.c
plat/qemu/qemu_bl2_setup.c
On Wed, Jun 20, 2018 at 6:58 AM Marek Vasut <marek.vasut at gmail.com> wrote:
>
> On 06/19/2018 09:11 AM, Laurent Pinchart wrote:
> > Hi Geert,
> >
> > On Tuesday, 19 June 2018 09:58:59 EEST Geert Uytterhoeven wrote:
> >> On Tue, Jun 19, 2018 at 4:15 AM Laurent Pinchart wrote:
> >>> On Sunday, 17 June 2018 03:08:02 EEST Marek Vasut wrote:
> >>>> On 06/16/2018 05:44 PM, Laurent Pinchart wrote:
> >>>>> On Saturday, 16 June 2018 02:42:30 EEST Marek Vasut wrote:
> >>>>>> On 06/16/2018 01:21 AM, Laurent Pinchart wrote:
> >>>>>>> On Friday, 15 June 2018 15:00:31 EEST Marek Vasut wrote:
> >>>>>>>> On 06/15/2018 01:43 PM, Marek Vasut wrote:
> >
> > [snip]
> >
> >>>>>>>>>>> Obvious design question is -- since you're adding new SMC call
> >>>>>>>>>>> anyway, can't the call just return the memory layout table
> >>>>>>>>>>> itself, so that it won't be duplicated both in U-Boot and ATF ?
> >>>>>>>>>>
> >>>>>>>>>> My gut feeling was to go with the smallest interface possible.
> >>>>>>>>>
> >>>>>>>>> But this doesn't scale. The API here uses some ad-hoc constants to
> >>>>>>>>> identify memory layout tables which have to be encoded both in ATF
> >>>>>>>>> and U-Boot, both of which must be kept in sync.
> >>>>>>>>>
> >>>>>>>>> The ATF already has those memory layout tables, it's only a matter
> >>>>>>>>> of passing them to U-Boot. If you do just that, the ad-hoc
> >>>>>>>>> constants and encoding of tables into U-Boot goes away and in fact
> >>>>>>>>> simplifies the design.
> >>>>>>>>>
> >>>>>>>>> Yet, I have to wonder if ATF doesn't already contain some sort of
> >>>>>>>>> standard SMC call to get memory topology. It surprises me that it
> >>>>>>>>> wouldn't.
> >>>>>>>>
> >>>>>>>> In fact, Laurent (CCed) was solving some similar issue with lossy
> >>>>>>>> decomp and I think this involved some passing of memory layout
> >>>>>>>> information from ATF to U-Boot too, or am I mistaken ?
> >>>>>>>
> >>>>>>> That's correct, ATF stores information about the memory layout at a
> >>>>>>> fixed address in system memory, and U-Boot can read it.
> >>>>>>
> >>>>>> Well, that sounds good ! Maybe we can avoid adding SMC call
> >>>>>> altogether then? :)
> >>>>>
> >>>>> I'd prefer that, yes.
> >>>>>
> >>>>> Let's not duplicate the mechanism used to pass FCNL information from
> >>>>> ATF to U- Boot, but instead create a data table format that can store
> >>>>> all the information we need, in an easily extensible way.
> >>>>>
> >>>>> To see how the mechanism is implemented for FCNL, search for 47FD7000
> >>>>> in the Renesas ATF sources
> >>>>> (git://github.com/renesas-rcar/arm-trusted-firmware.git).
> >>>>
> >>>> For everyone involved, can you explain what FCNL is ? ;-)
> >>>
> >>> FCNL is Frame Compression Near Lossless. It's a way to reduce memory
> >>> bandwidth by transparent compression and decompression of video frames.
> >>> Compression is handled by an IP core called FCP, and decompression is
> >>> handled by the DRAM controller. ATF programs the DRAM controller with
> >>> ranges of memory addresses that will be dynamically decompressed. The
> >>> registers containing those ranges are accessible in secure mode only, so
> >>> neither U-Boot nor Linux can read them. That's why ATF has to pass the
> >>> information to U-Boot, in order to add the ranges as reserved memory in
> >>> DT.
> >>>
> >>>> Any yes, I agree this sounds good. I had a discussion on the U-Boot IRC
> >>>> about passing the memory configuration around and the result is
> >>>> basically the same -- pass a table from ATF to U-Boot. If there's
> >>>> already something, great.
> >>
> >> Pass a "table"? Or an FDT containing the /memory nodes?
> >> The latter allows for easier future extension.
> >
> > ATF passes a table to U-Boot, and U-Boot then updates the FDT accordingly
> > before starting Linux.
>
> At this point, U-Boot does not parse any such table. It could be some
> fork does that, but mainline does not. But that code could (and probably
> should) be added.
>
> I don't think ATF has FDT support, but I might be wrong. And if ATF can
> pass DT fragment or some simple DT, that'd be neat.
>
> --
> Best regards,
> Marek Vasut
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