[alsa-devel] [PATCH 1/8] soundwire: intel: filter SoundWire controller device search

[Pierre-Louis Bossart]

>>>> +	/*
>>>> +	 * On some Intel platforms, multiple children of the HDAS
>>>> +	 * device can be found, but only one of them is the SoundWire
>>>> +	 * controller. The SNDW device is always exposed with
>>>> +	 * Name(_ADR, 0x40000000) so filter accordingly
>>>> +	 */
>>>> +	if (adr != 0x40000000)
>>>
>>> I do not recall if 4 corresponds to the links you have or soundwire
>>> device type, is this number documented somewhere is HDA specs?
>>
>> I thought it was a magic number, but I did check and for once it's
>> documented and the values match the spec :-)
>> I see in the ACPI docs bits 31..28 set to 4 indicate a SoundWire Link Type
>> and bits 3..0 indicate the SoundWire controller instance, the rest is
>> reserved to zero.
> 
> So in that case we should mask with bits 31..28 and match, who knows you
> may have multiple controller instances in future

yes, I was planning on only using the link type.

> I had a vague recollection that this was documented in the spec, glad
> that in turned out to be the case.
> 
> Btw was the update to HDA spec made public?

Not that I know of. The previous NHLT public doc has actually 
disappeared from the Intel site and I can't find it any longer, so 
currently the amount of public documentation is trending to zero :-(

> 
>>> Also it might good to create a define for this
>>
>> I will respin this one to add the documentation above, and only filter on
>> the 4 ms-bits. Thanks for forcing me to RTFM :-)
>