[PATCH 1/2] Makefile: Add environment variable DEVICE_TREE to header

[Simon Glass]

Hi Michal,

On Mon, 2 Mar 2020 at 23:52, Michal Simek <michal.simek at xilinx.com> wrote:
>
> On 02. 03. 20 20:47, Simon Glass wrote:
> > Hi Michal,
> >
> > On Fri, 28 Feb 2020 at 04:03, Michal Simek <michal.simek at xilinx.com> wrote:
> >>
> >> On 26. 02. 20 16:33, Simon Glass wrote:
> >>> Hi Michal,
> >>>
> >>> On Tue, 18 Feb 2020 at 09:02, Michal Simek <michal.simek at xilinx.com> wrote:
> >>>>
> >>>> Users have option to overwrite default device tree
> >>>> (CONFIG_DEFAULT_DEVICE_TREE) via environment variable DEVICE_TREE.
> >>>>
> >>>> Feature has been added long time ago by commit 74de8c9a1672
> >>>> ("dts/Makefile: Build the user specified dts") for a little bit different
> >>>> reason.
> >>>>
> >>>> But this variable can be also used for different purpose like choosing
> >>>> proper configuration from FIT image in SPL.
> >>>> And this is the functionality I would like to use on Xilinx Zynq devices
> >>>> that current u-boot.img can be composed in the same way based on OF_LIST
> >>>> and different configuration is taken based on platform specific SPL.
> >>>> SPL requires low level ps7_init_gpl configuration that's why different
> >>>> boards require different SPL with fixed board_fit_config_name_match().
> >>>>
> >>>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
> >>>> ---
> >>>>
> >>>> I have done it in this way but maybe there is any smarter way how this can
> >>>> be done. Also macro name can change if you want.
> >>>
> >>> Can you please add a bit of documentation to doc/README.fdt-control ?
> >>
> >> This feature is cover by documentation in this file already. What
> >> exactly do you think that should be added?
> >>
> >
> > Then I suppose I am confused as to what this patch does. I thought it
> > was allowing U-Boot to pass the DT to Linux, which wasn't previously
> > supported?
>
> Just a note this is also not supported and would be good to have support
> for it.
>
> The patch is putting device tree name as macro to header and I am using
> this value just in zynq SPL to choose proper dtb file from u-boot.img.
>
> On ZynqMP generic platform I am using mkimage_fit_atf.sh script to
> automatically fill default configuration.
> https://gitlab.denx.de/u-boot/u-boot/blob/master/arch/arm/mach-zynqmp/mkimage_fit_atf.sh#L94
> And I didn't want to create different u-boot.img/itb for Zynq that's why
> SPL has device tree built it directly in SPL.
>
> As I said maybe there is smarter way how to do it but this was the one I
> used.
> In our case SPL another way could be to put filename from ps7_init_*
> files and save it as variable and use it.

OK I see. So are you using OF_CONTROL for SPL?

Regards,
Simon