[U-Boot] [PATCH] tegra: trimslice: fix a couple typos

[Stephen Warren <swarren@wwwdotorg.org>]

On 06/01/2012 12:38 AM, Igor Grinberg wrote:
> On 05/31/12 19:50, Stephen Warren wrote:
>> On 05/31/2012 04:13 AM, Marek Vasut wrote:
>>> Dear Igor Grinberg,
>>>
>>>> On 05/30/12 19:45, Stephen Warren wrote:
>>>>> From: Stephen Warren <swarren@nvidia.com>
>>>>>
>>>>> Fix the .dts file USB unit addresses not to duplicate each-other.
>>>>>
>>>>> Fix the board name string to indicate the vendor is Compulab not NVIDIA.
>>>>>
>>>>> Signed-off-by: Stephen Warren <swarren@nvidia.com>
>>>>
>>>> Acked-by: Igor Grinberg <grinberg@compulab.co.il>
>>>
>>> Do we have one copy of the dts files here and one in Linux kernel tree? Are they 
>>> the same?
>>
>> Both U-Boot and the kernel have their own copies of the .dts files.
>>
>> In general, the U-Boot copy would be identical to what's in the kernel,
>> or a pure subset since mostly the kernel's driver support is more
>> advanced, so we've added more nodes to the DT.
>>
>> That said, there are unfortunately some bizarre quirks in the way the
>> U-Boot parses the device tree, such as requiring the /aliases node in
>> order to enumerate at least some devices, the use of the Tegra clock
>> binding that hasn't been incorporated into the kernel yet and is used
>> for both clock and module reset functionality even though it's really
>> only intended for clock functionality, and various other small
>> properties that are U-Boot specific (although I forget if we managed to
>> eliminate these all or not). These all end up causing differences
>> between the two device tree files:-(
> 
> Thanks for the information.
> 
> I don't see any problem with having differences between the .dts files
> in kernel and U-Boot, because the way I see it:

The issue isn't so much the duplicate files, but differing content.

The whole point about DT is that it's a pure representation of the
hardware; there should be no software-dependent design or data in it.
Put another way, both U-Boot and the Linux kernel (and indeed anything
else) should expect the DT to be written according to the same
"bindings" design. This doesn't preclude the U-Boot DT file being a
strict subset of the kernel file it it needs less information, but what
is in both should match.

> Also, IIRC, the intension was to remove the kernel .dts files after
> "all bootloaders" know to boot the DT kernel...

I don't believe it's anything to do with bootloaders. Bootloaders are
already (in the main) expected to provide the DTB to the kernel as a
separate entity, irrespective of whether the DTB is built by the kernel
boot process or from some other repository. (Although there is
CONFIG_APPENDED_DTB to support cases where this isn't possible, it's
much preferred not to use this). Moving the .dts files out of the kernel
is more purely about finding a place to put them I think.