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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <47fd3ca6-6910-f101-9b63-f653cd1443f9@linux.intel.com>
Date:   Tue, 7 May 2019 09:43:15 -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 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 :-)