[PATCH] ARM: Distro boot: document the need for fdtfile variable to be set

[Dennis Gilmore]

On Thu, Sep 3, 2020 at 3:24 PM Stephen Warren <swarren at wwwdotorg.org> wrote:
>
> On 9/3/20 2:14 PM, Dennis Gilmore wrote:
> > On Thu, Sep 3, 2020 at 2:15 PM Stephen Warren <swarren at wwwdotorg.org> wrote:
> >>
> >> On 9/3/20 10:40 AM, Dennis Gilmore wrote:
> >>> When testing builds provided in https://github.com/openwrt/openwrt/pull/3360
> >>> I discovered that fdtfile was not set and as a result the firmware was not
> >>> functional. So I am documenting what is needed.
> >>>
> >>> Signed-off-by: Dennis Gilmore <dennis at ausil.us>
> >>>
> >>> Cc: Atish Patra <atish.patra at wdc.com>
> >>> Cc: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
> >>> Cc: Tom Rini <trini at konsulko.com>
> >>> Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
> >>> Cc: Vagrant Cascadian <vagrant at debian.org>
> >>> Cc: Stephen Warren <swarren at nvidia.com>
> >>> Cc: Karsten Merker <merker at debian.org>
> >>> ---
> >>>  doc/README.distro | 8 ++++++++
> >>>  1 file changed, 8 insertions(+)
> >>>
> >>> diff --git a/doc/README.distro b/doc/README.distro
> >>> index 5076bebd18..3eb70aeb14 100644
> >>> --- a/doc/README.distro
> >>> +++ b/doc/README.distro
> >>> @@ -224,6 +224,14 @@ fdt_addr_r:
> >>>
> >>>    A size of 1MB for the FDT/DTB seems reasonable.
> >>>
> >>> +fdtfile:
> >>> +
> >>> +  Mandatory. the name of the DTB file for the specific board for instance
> >>> +  the espressobin v5 board the value is "marvell/armada-3720-espressobin.dtb"
> >>> +  while on a clearfog pro it is "armada-388-clearfog-pro.dtb" in the case of
> >>> +  a board providing its firmware based DTB this value can be used to override
> >>> +  the DTB with a different DTB.
> >>
> >> IIRC this variable isn't mandatory; if the DT filename follows expected
> >> ${soc}-${board}.dtb naming, then U-Boot has a default value that will
> >> work without the user or U-Boot author having to manually set this variable.
> >>
> >> So it's certainly mandatory that U-Boot know this value at runtime, but
> >> perhaps the text should be expanded to indicate that sometimes U-Boot
> >> can provide the value itself, but sometimes the variable needs to be set?
> >
> > in include/config_distro_bootcmd.h we have the following
> > /*
> >  * On 32bit ARM systems there is a reasonable number of systems that follow
> >  * the $soc-$board$boardver.dtb name scheme for their device trees. Use that
> >  * scheme if we don't have an explicit fdtfile variable.
> >  */
> > #define BOOTENV_EFI_SET_FDTFILE_FALLBACK                                  \
> >         "if test -z \"${fdtfile}\" -a -n \"${soc}\"; then "               \
> >           "setenv efi_fdtfile ${soc}-${board}${boardver}.dtb; "           \
> >         "fi; "
> > #else
> > #define BOOTENV_EFI_SET_FDTFILE_FALLBACK
> > #endif
> >
> > that schema is not true on AArch64 and the method only works with efi
> > booting. I will update the text to list out the conditions you could
> > get away with not setting the variable
>
> I was thinking more of cmd/pxe_utils.c:label_boot(), which covers the
> extlinux.conf rather then EFI case. This certainly applies to both 32-
> and 64-bit Tegra systems at least.
>
> Specifically:
> >                        f1 = env_get("fdtfile");
> >                         if (f1) {
> >                                 f2 = "";
> >                                 f3 = "";
> >                                 f4 = "";
> >                         } else {
> >                                 /*
> >                                  * For complex cases where this code doesn't
> >                                  * generate the correct filename, the board
> >                                  * code should set $fdtfile during early boot,
> >                                  * or the boot scripts should set $fdtfile
> >                                  * before invoking "pxe" or "sysboot".
> >                                  */
> >                                 f1 = env_get("soc");
> >                                 f2 = "-";
> >                                 f3 = env_get("board");
> >                                 f4 = ".dtb";
> >                         }

That still only covers the 32-bit case, at least unless the OS is
removing the vendor directory from the dtbs. At least for fedora on
aarch64 we leave the vendor directories in place

ls /boot/dtb/
allwinner  amlogic  arm       cavium     hisilicon  nvidia  rockchip
amd        apm      broadcom  freescale  marvell    qcom    xilinx

though fedora is only supporting efi on AArch64

Dennis