Defining schemas for Device Tree

[jonsmirl at gmail.com]

On Tue, Jul 30, 2013 at 2:03 PM, jonsmirl at gmail.com <jonsmirl at gmail.com> wrote:
> On Tue, Jul 30, 2013 at 1:49 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 07/30/2013 11:45 AM, jonsmirl at gmail.com wrote:
>>> On Tue, Jul 30, 2013 at 1:34 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>>>> 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
>>>
>>> The PowerPC FDT doc says that strings are indirected into a string
>>> table. So they aren't variable length in the data structures.
>>
>> Do you have a link to the document; I'm not sure which one you mean.
>
> So it looks like there is one indirection to get to the block, then
> the strings are concatenated. The indirection must have been hidden
> when the node structure was created.  I had thought that there was a
> list of indirects each pointing to a string in the string block.
>
> https://www.power.org/documentation/epapr-version-1-1/

So what does an alternating use of strings do?

 dmas = "tx", <&pdma0 7>, "rx", <&pdma0 6>;


>
> 8.5 Strings Block
> The strings block contains strings representing all the property names
> used in the tree. These null-
> terminated strings are simply concatenated together in this section,
> and referred to from the structure
> block by an offset into the strings block.
> The strings block has no alignment constraints and may appear at any
> offset from the beginning of the
> device tree blob.
>
>
>>
>>> I was wondering how dmas = "tx", "rx" was implemented. It is two
>>> pointers into the indirect block. So this should work, there is no
>>> variable length data to worry about in the structure.
>>
>> If you look at of_property_read_string_index() in drivers/of/base.c,
>> you'll see that it expects the strings to just be packed together inline.
>>
>> What you say may be correct for node and property names, just not
>> property values.
>
>
>
> --
> Jon Smirl
> jonsmirl at gmail.com



-- 
Jon Smirl
jonsmirl at gmail.com