[U-Boot] [PATCH] jetson-tk1: Set fdtfile environment variable

[Stephen Warren]

On 04/13/2016 11:21 AM, Alexander Graf wrote:
>
>
>> Am 13.04.2016 um 19:00 schrieb Stephen Warren <swarren at wwwdotorg.org>:
>>
>>> On 04/13/2016 09:51 AM, Alexander Graf wrote:
>>>> On 04/13/2016 05:31 PM, Stephen Warren wrote:
>>>>> On 04/13/2016 06:55 AM, Andreas Färber wrote:
>>>>>> Am 13.04.2016 um 14:48 schrieb Andreas Färber:
>>>>>> The 4.5.0 kernel cannot cope with U-Boot's internal device tree, and
>>>>>> the
>>>>>> distro boot commands are looking for $fdtfile, so provide it to avoid
>>>>>> having users supply a dumb boot.scr doing a setenv fdtfile ...; boot,
>>>>>> defeating the purpose of generic EFI boot.
>>>>>>
>>>>>> Cc: Stephen Warren <swarren at nvidia.com>
>>>>>> Cc: Alexander Graf <agraf at suse.de>
>>>>>> Signed-off-by: Andreas Färber <afaerber at suse.de>
>>>>>> ---
>>>>>>   include/configs/jetson-tk1.h | 4 ++++
>>>>>>   1 file changed, 4 insertions(+)
>>>>>>
>>>>>> diff --git a/include/configs/jetson-tk1.h
>>>>>> b/include/configs/jetson-tk1.h
>>>>>> index 59dbb20..82a4be4 100644
>>>>>> --- a/include/configs/jetson-tk1.h
>>>>>> +++ b/include/configs/jetson-tk1.h
>>>>>> @@ -63,6 +63,10 @@
>>>>>>   /* General networking support */
>>>>>>   #define CONFIG_CMD_DHCP
>>>>>>
>>>>>> +#define BOARD_EXTRA_ENV_SETTINGS \
>>>>>> +    "fdtfile=tegra124-jetson-tk1.dtb\0" \
>>>>>> +    ""
>>>>>
>>>>> Is there any more intelligent solution than doing this for each board?
>>>>
>>>> Yes, the distro boot scripts shouldn't be using $fdtfile
>>>> unconditionally since it's not guaranteed to be set. The model is that
>>>> boot scripts determine the FDT filename, and $fdtfile is an optional
>>>> override.
>>>
>>> The point of all of the efi magic is that we can completely get rid of
>>> boot scripts. Boards use the distro scripts, everything else gets
>>> implicitly detected and executed. The way other boards deal with common
>>> code mapping into separate boards is to either implement a "findfdt"
>>> scriptlet or directly write the fdtfile variable (e.g. beaglebone) in
>>> board init (e.g. rpi).
>>>
>>>> It looks like the hard-coded use of $fdtfile was added into the EFI
>>>> path, which I didn't get to review, and which shouldn't be enabled by
>>>> default but unfortunately is.
>>>
>>> s/un// :)
>>>
>>> Just imagine a world where people don't have to worry about bootloaders
>>> anymore. Things would "just work". You plug in a usb stick, it comes up,
>>> boots Linux, everthing goes without anyone touching boot scripts,
>>> downloading board specific files, etc. You could get a random
>>> distribution from a common download page from somewhere and just run it.
>>>
>>> Well, you can also just look at any random x86 system. They get at least
>>> that part pretty right these days.
>>
>> Well, you can also get the same benefit using extlinux.conf, and without relying on EFI:-P
>>
>> Anyway, nothing in your benefits-of-EFI statement implies that relying on $fdtfile being set is correct. That's a new requirement that didn't exist before. Either the requirement needs to be removed (e.g. using a default FDT filename such as "${soc}-${board}${boardver}.dts") or only enabling this functionality on boards that do set $fdtfile, since it relies on that.
>
> On boards that fon't set fdtfile we just don't load it, because we can't find the file. So you're getting a working grub2 payload, but Linux gets an empty device tree unless you pass it in using the grub2 "devicetree" command.
>
> It's really just a convenience helper. And a nice piece to the puzzle that by convention allows users to think less about u-boot internals. The efi code works fine without.

Except for the fact that it doesn't just work, since if it did there 
wouldn't be a need for the patch in this email thread.

I think the correct fix is to abandon this patch, and have the EFI code 
(i.e. the scripts in the distro boot commands most likely) calculate a 
default value for $fdtfile if it isn't already set. Something like:

if test -n "${fdtfile}"; then
     set _fdt ${fdtfile};
else
     set _fdt ${soc}-${board}${boardver}.dtb;

... and use ${_fdt} instead of relying on ${fdtfile}.

If you still want to pursue this patch, it should be enhanced to cover 
all boards where the EFI code is enabled and $fdtfile isn't already set 
somehow, which I expect is almost all U-Boot boards since the Kconfig 
option is "default y".