[Ksummit-2013-discuss] Defining schemas for Device Tree

Stephen Warren swarren at wwwdotorg.org
Tue Jul 30 17:49:26 UTC 2013


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.

> 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.


More information about the Ksummit-2013-discuss mailing list