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

From: Pierre-Louis Bossart
Date: Tue May 07 2019 - 10:44:09 EST

On 5/7/19 7:26 AM, Vinod Koul wrote:
On 03-05-19, 19:29, Pierre-Louis Bossart wrote:
The convention is that the SoundWire controller device is a child of
the HDAudio controller. However there can be more than one child
exposed in the DSDT table, and the current namespace walk returns the
last device.

Add a filter and terminate early when a valid _ADR is provided,
otherwise keep iterating to find the next child.

So what are the other devices in DSDT here..

this is what I see:

Scope (HDAS)
Device (IDA)
Name (_ADR, 0x00020001) // _ADR: Address

I thought this was nonsense but your question triggered me to look into the Intel SST ACPI specs (not public I am afraid but shared with the OS who shall not be named).
Using the same source of information as below, I *believe* this is HDaudio related, bits 31..16 mean HDaudio with codec SDI 2, and NodeId 1 for the function group. This would make sense as I believe there are two codecs on the board that can be pin-strapped to boot either in HDaudio or SoundWire mode- but this is a conjecture only.

At any rate, we need a hardware rework and mutual exclusion between HDaudio and SoundWire, so we have to ignore this one when SoundWire is enabled.

+ /*
+ * 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.

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 :-)