[U-Boot] [PATCH 0/2] Standardize on run-time board ID variables

[Simon Glass]

Hi,

On Wed, Oct 24, 2012 at 12:05 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 10/24/2012 12:41 PM, Tom Rini wrote:
>> On Wed, Oct 24, 2012 at 11:50:38AM -0600, Stephen Warren wrote:
>>> On 10/24/2012 11:28 AM, Tom Rini wrote:
>>>> Hey all,
>>>>
>>>> I've been thinking about one of the problems we need to solve
>>>> over in TI AM335x land and that is given that we support a
>>>> number of different boards with a single binary (and we have an
>>>> i2c eeprom that tells us what board and revision we are on),
>>>> the user needs to be able to easily determine what board we are
>>>> on so they know what dtb file to load so they can boot.  To
>>>> this end I've added CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG to the
>>>> README which says when set we have board_name and board_rev set
>>>> at run-time.  Then for am335x[1]
>>>
>>> With CONFIG_ENV_VARS_UBOOT_CONFIG set, there's a environment
>>> variable named $board that indicates which board U-Boot is
>>> running on (and other related variables). The idea is that the
>>> user can:
>>>
>>> fsload ${devtype} ${devnum}:${rootpart} ${fdt_addr_r}  \
>>> /boot/${soc}-${board}.dtb
>>>
>>> Now, CONFIG_ENV_VARS_UBOOT_CONFIG sets $board at compile-time,
>>> since the config variable was created in the context on a U-Boot
>>> that runs on a single board. However, I see no reason why we
>>> can't maintain the user-visible results of this config option
>>> even in other cases, so that everything is consistent to the
>>> user
>>
>> This works assuming that board maps to the device tree name.  A bit
>> more below...
>
> True. I've made sure of that for Tegra.
>
>>> To that end, can we make CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG set
>>> $board instead of $board_name?
>>
>> I had talked with Joe about this on IRC briefly and he seemed to
>> be against overwriting "board"
>
> Why is that? Perhaps alternatively, CONFIG_ENV_VARS_UBOOT_CONFIG
> should set both board and a default value for board_name.
>
>>> Adding $board_rev sounds like a very good idea; the filename in
>>> the above command could be modified to:
>>>
>>> ${soc}-${board}${boardrev}.dtb
>>
>> Indeed, I know we'll need to do this in the future for one of the
>> boards in this family.
>>
>>> Or, do you think it'd be better for boot.scr to always reference
>>> $fdtfile, and so modify Tegra's default environment to derive
>>> $fdtfile from $soc, $board, $boardrev?
>>
>> Or uEnv.txt, but yes, fdtfile seems to be the standard variable
>> name for the device tree to use.
>
> Ah, I do see quite a few U-Boot config headers defining that.
>
>> Doing something to derive this also means that custom development
>> can be a bit easier too since you can just set fdtfile directly and
>> work out the logic for auto-detection later.
>
> Hmm. So I can't really put the following into Tegra's default environment:
>
> "fdtfile=${soc}-${board}${boardrev}.dtb"
>
> ... since that would require any use of "${fdtfile}" in a command to
> first expand fdtfile itself, then expand it a second time to pick up
> the actual soc/board/... values, and that's not how the shell works.
>
> That implies that e.g. Tegra's scriptboot (seed BOOTCMDS_COMMON in
> include/configs/tegra-common-post.h) would need to do something like:
>
> setenv fdtfile ${soc}-${board}${boardrev}.dtb
>
> ... before executing the loaded boot.scr. But then, how would it know
> whether to do that, or whether the user wanted to override the fdtfile
> value?
>
> In theory, I could do the following in Tegra's default environment:
>
> "fdtfile=" CONFIG_SYS_SOC "-" CONFIG_SYS_BOARD" ".dtb"
>
> But then that wouldn't allow for the fdtfile value to vary at run-time
> based on $boardrev.

I did create a patch to make environment variables recursive. It is a
right pain to have to 'setenv' them to get them to work in this way.
However I wasn't really sure how to control it. Can we just move to
recursive environment variable evaluation, or would that break things?
Perhaps a CONFIG_ option?

Re this discussion, if the board itself can detect its revision then
great. If it can't, then presumably the factory process writes the
correct fdt to the board during manufacture.

>
>> Also not hard-coding in the path makes it easier for whichever
>> distro to fill in that logic.
>
> By the path, do you mean "/boot", or the way the filename is
> construced? "/boot" in my fsload example above was a quote from the
> boot.scr I use, not something U-Boot provides, so I'd expect distros
> could customize it to their needs. If you mean the filename - I'd
> certainly advocate enforcing that U-Boot and the kernel board names
> and DT filenames be in sync.
>
>>
>>> (This general discussion might usefully happen on the
>>> cross-distro mailing list too?)
>>
>> Yes.  Where? :)
>
> cross-distro at lists.linaro.org
> ______________________________________

Regards,
Simon