linux-kernel - Re: [PATCH 1/8] soundwire: intel: filter SoundWire controller device search

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Date:   Wed, 8 May 2019 11:20:10 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, gregkh@...uxfoundation.org,
        liam.r.girdwood@...ux.intel.com, jank@...ence.com, joe@...ches.com,
        srinivas.kandagatla@...aro.org,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [PATCH 1/8] soundwire: intel: filter SoundWire controller device
 search


>>>> +	/*
>>>> +	 * 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 :-)
>