Re: [Patch V7 02/10] ASoC: qcom: Document LPASS CPU bindings

From: Kumar Gala
Date: Fri Mar 06 2015 - 17:07:03 EST



On Mar 6, 2015, at 4:03 PM, Kenneth Westfield <kwestfie@xxxxxxxxxxxxxx> wrote:

> On Fri, Mar 06, 2015 at 10:07:01AM -0600, Kumar Gala wrote:
>> On Mar 5, 2015, at 7:51 PM, Kenneth Westfield <kwestfie@xxxxxxxxxxxxxx> wrote:
>>> On Thu, Mar 05, 2015 at 12:52:30PM -0600, Kumar Gala wrote:
>>>> On Mar 3, 2015, at 6:21 PM, Kenneth Westfield <kwestfie@xxxxxxxxxxxxxx> wrote:
>>>>
>>>>> +++ b/Documentation/devicetree/bindings/sound/qcom,lpass-cpu.txt
>>>>> @@ -0,0 +1,49 @@
>>>>> +* Qualcomm Technologies LPASS CPU DAI
>>>>> +
>>>>> +Required subnodes:
>>>>> +
>>>>> +- qcom,adsp : Audio DSP sub-node
>>>>> +
>>>>> +Optional Audio DSP subnode properties:
>>>>> +
>>>>> +- status : "disabled" indicates the adsp is not available.
>>>>> +
>>>>
>>>> What is the intent of this subnode?
>>>>
>>>
>>> From the cover letter:
>>> Even though the ipq806x LPASS does not contain an audio DSP, other SOCs
>>> do have one. For those SOCs, the audio DSP typically controls the
>>> hardware blocks in the LPASS. Hence, different CPU DAI driver(s) would
>>> need to be used in order to facilitate audio with the DSP. As such, the
>>> LPASS DT contains an adsp subnode, which is disabled for this SOC. The
>>> same subnode should be enabled and populated for other SOCs that do
>>> contain an audio DSP. Not using the audio DSP would require different
>>> CPU DAI driver(s), in addition to possible bootloader and/or firmware
>>> changes.
>>>
>>> This was the result of a request from Mark. See here:
>>> http://thread.gmane.org/gmane.linux.drivers.devicetree/109331/focus=11633
>>
>> Two quick comments before I read Mark?s comments.
>>
>> 1. Its not normal practice to put something into a DT that does not exist. Having a node, but marking it disabled implies existence.
>
> Will change the DT definition to optional.
>
>> 2. How would one normally address the audio DSP if it did exist. I?m just wondering if having a subnode is the proper solution vs maybe a phandle
>
> The audio DSP is, in fact, contained within the audio subsystem. The
> representation of that relationship in the DT, I believe, would be a subnode.
> OTOH, if there is a strong sentiment towards using a phandle, that would be
> fine with me.

Just depends on how we communicate with the DSP. If its mostly via MMIO access than a sub node makes sense. If its via some other RPC/communication mechanism than possibly a phandle. Trying to understand a bit more to than see what I’d recommend.

- k

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