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

[Alexander Graf]

> 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.


Alex