[alsa-devel] [RFC 00/10] Enable HDA Codec support on Intel Platforms (Series2)

[Pierre-Louis Bossart]

On 12/3/17 9:22 PM, Vinod Koul wrote:
> On Sun, Dec 03, 2017 at 09:15:21PM -0600, Pierre-Louis Bossart wrote:
>> On 12/3/17 11:20 AM, Vinod Koul wrote:
>>> On Fri, Dec 01, 2017 at 09:03:25PM +0100, Takashi Iwai wrote:
>>>>>>> FIXME:
>>>>>>> - KConfig changes does not look right, but I could not think of any proper
>>>>>>>     way without making changes into legacy HDA codec driver. So need some
>>>>>>>     help on this topic.
>>>>>>
>>>>>> And this is another big issue.  As long as you don't allow build both,
>>>>>> it never flies with distros, and it means no dramatic improvement of
>>>>>> the situation, either.
>>>>>>
>>>>>> IOW, we have to make the codec driver working on both controller/bus
>>>>>> implementations, and it essentially means to rewrite the HD-audio
>>>>>> codec plumbing code.  Currently, it's a kind of half-baked state, and
>>>>>> we need to cast to unified form.
>>>>>
>>>>> Before going into codec support, should we first deal with the
>>>>> selection of the ASoC/Legacy mode for the controller side of things?
>>>>> Even with basic HDMI/iDisp cases, we don't have a clean solution
>>>>> today. When I worked on the late Joule platform, there was no fallback
>>>>> mode which forced a recompilation depending on BIOS settings.
>>>>> My understanding is that there is no support for multiple drivers
>>>>> registering for the same PCI ID, I believe we'll have to define a
>>>>> top-level wrapper which arbitrates internally based on BIOS settings
>>>>> and user/distro preferences which mode is selected.
>>>>
>>>> True, we need to sort out that.  But the selection of the card-level
>>>> driver can be relatively easily done in a manual way, either via
>>>> blacklisting or by common module options.  Currently AMDGPU and radeon
>>>> drivers are in such situation, for example.
>>>>
>>>> A common single switch, or at best the automatic arbitration would be
>>>> preferred, of course, though.
>>>
>>> The switch is again short term as we should progress and move towards one
>>> solution whilst deprecating the other, so that way this makes a simple
>>> solution and helps in transition, change flag defaults and deprecate.
>>
>> Sorry, I don't get your point. Are you saying the legacy would be
>> deprecated? that was never my understanding, Rakesh's patches only make it
>> easier to use the DSP in combination with an HDaudio codec, but if the DSP
>> is not present the legacy is the fallback, no?
> 
> for now yes, but what prevents us from supporting coupled mode when DSP is
> disabled :)

That gets complicated. you'd have
1. DSP-based ASoC driver for SKL+ w/ DSP
2. coupled-mode ASoC driver for SKL+ w/o DSP
3. legacy for pre-SKL platforms.

I don't see what simplification this brings, it's complicated enough 
with 1. and 3, and legacy is not going away.