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

[Simon Glass]

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?

Regards,
Simon


> Thanks,
> Michal
>
> 169 Build:
> 170
> 171 After board configuration is done, fdt supported u-boot can be build
> in two ways:
> 172 1)  build the default dts which is defined from
> CONFIG_DEFAULT_DEVICE_TREE
> 173     $ make
> 174 2)  build the user specified dts file
> 175     $ make DEVICE_TREE=<dts-file-name>
> 176
> 177
>