Defining schemas for Device Tree

[Stephen Warren]

On 07/30/2013 11:29 AM, jonsmirl at gmail.com wrote:
> On Tue, Jul 30, 2013 at 1:19 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>
>> On 07/30/2013 07:14 AM, jonsmirl at gmail.com wrote:
>>> On Tue, Jul 30, 2013 at 6:25 AM, Mark Brown <broonie at kernel.org> wrote:
>>>> On Mon, Jul 29, 2013 at 08:30:29PM -0400, jonsmirl at gmail.com wrote:
>>>>
>>>>> This...
>>>>> tx-dma-channel = <&pdma0 7>; /* preliminary */
>>>>> rx-dma-channel = <&pdma0 6>; /* preliminary */
>>>>
>>>>> Probably should be
>>>>> dmas = <&pdma0 7>,<&pdma0 6>;
>>>>> dma-names = "tx", "rx";
>>>>
>>>> It should be - the latter is the generic DMA binding.  There's a lot of
>>>> bindings in the kernel that predate that but people are currently
>>>> working to transfer over, this is one of the examples of instability
>>>> that everyone is talking about.
>>>
>>> Is something similar to this possible in device tree syntax?
>>> dmas =  <"tx" &pdma0 7>,  <"rx"  &pdma0 6>;
>>
>> I /think/ you can physically write that in *.dts, or something very
>> similar; with the strings outside the <>:
>>
>> dmas = "tx", <&pdma0 7>, "rx", <&pdma0 6>;
>>
>> However, there's been strong push-back (i.e. doing that has not been
>> allowed at all) on attempting to mix variable-length strings and
>> fixed-length/alignment integer cells in the same property. This is
>> primarily because you then can't ensure that the integer cell data is
>> aligned in the DTB (dtc and/or the DTB format spec does/requires/allows
> 
> Can we turn the strings into string phandles? Then they'd be fixed sized.

I believe that phandles point at nodes not arbitrary data, so no.

Now, could the DTB format be enhanced to allow that? Perhaps, although
we'd need a different string syntax to enable it, since existing
bindings would require the current inline-string format. That's getting
outside the realm of schemas and making active changes to the DT format
though...

> That might provide a way to internationalize the strings too.

I don't think internationalization is needed; DT is an interface to
drivers/SW, rather than something end-user-visible.