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

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Message-ID: <20190508163717.GX16052@vkoul-mobl>
Date:   Wed, 8 May 2019 22:07:17 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
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 08-05-19, 11:20, Pierre-Louis Bossart wrote:
> 
> > > > > +	/*
> > > > > +	 * 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 :-)

Yeah about that someone was indeed complaining about that on IRC, it is
shame that link is valid but doc is gone... check with Rakesh or someone
they might have a copy...

-- 
~Vinod