Re: [PATCH v2 0/7] ASoC: Intel: avs: Soundwire support

[Pierre-Louis Bossart <pierre-louis.bossart@linux.dev>]

On 11/4/26 15:31, Cezary Rojewski wrote:
> On 11/4/2026 2:33 PM, Vinod Koul wrote:
>> On 04-11-26, 12:52, Pierre-Louis Bossart wrote:
>>> On 11/4/26 10:14, Cezary Rojewski wrote:
>>>> On 11/3/2026 6:20 PM, Pierre-Louis Bossart wrote:
>>>>>
>>>>>> Also, the existing code fetches the PDIs based on pre-defined "dai_id".
>>>>>> That's not the case for the avs-driver.  It simply asks: "is any PDI
>>>>>> free?" and assigns it for the substream if one is found.
>>>>>> No predefining.  Again, this aligns with how HDAudio streaming is done.
>>>>> Yeah but at the end of the day there's a 1:1 mapping between cpu_dai and
>>>>> PDI, no?
>>>>>
>>>>> All PDIs are created equal, a dynamic mapping doesn't make things more
>>>>> efficient. It just makes things more complex to debug since you don't
>>>>> have a fixed mapping between dailinks/stream/cpu_dai/PDI.
>>>>>
>>>>> Put differently, couldn't the AVS driver work around that fixed mapping
>>>>> to avoid changes to legacy platforms that have shipped many moons ago?
>>>>
>>>> Kind disagree on the debugging part.  Having SDW streaming follow
>>>> closely to what is done for HDAudio from the beginning (no hardcodes)
>>>> makes it easier for a developer to debug stuff.  OTOH if one of these
>>>> two follows a completely different path, the developer has to have such
>>>> hardcodes in mind when debugging the PCM code or even when looking at
>>>> the topology.
>>>>
>>>> At the same time, I'm not going anywhere and I do intend to work with
>>>> Peter and Kai to update the common code. Simply put, such a refactor
>>>> would be routed through SOF GH first.
>>> The machine driver selects the first available cpu_dai when creating a
>>> dailink. It doesn't really add much value to add a second level of
>>> freedom to select PDIs, since in practice it'll select the first as
>>> well. PDIs have no moral equivalent in HDaudio, it's a Cadence-specific  IP.
>>>
>>> Also there is already a degree of freedom in the allocation of
>>> stream_tag, which is used for DMA support. That one makes sense since
>>> DMAs may be used for non-SoundWire things (HDMI, trace, probe, etc).
>>>
>>> That's 2 degrees of freedom on 3 levels, do you really need full
>>> configurability?
> 
> I'm not following this "level of freedom" notion. What's part of this
> set is a basic allocation - driver (a user of the soundwire-lib) comes
> and ask for a free resource (PDI). If there is one, it gets assigned.
> Very standard, how many expect resources are redistributed.

You're missing a level. The platform driver exposes a set of DAIs, and
then the machine driver will decide which dai it needs for a specific
dailink/stream. That's the part that really matters IMHO.

The choice of the PDI is done only internally in the Intel platform
driver, and it really doesn't matter how you map cpu_dais to PDIs. A
fixed mapping is just as good as a dynamic approach - same results,
maybe less elegant but the performance is identical.

>> I dont see any gain from this approach. I would reconsider and see if we
>> can reuse things
>>
> 
> I'm not sure which way the last message goes.
> 
> However, I find it easier to move from hardcodes to the basic allocation
> approach (seen here, in this very patchset) than the other way around.
> The change would consist of updating intel_hw_params() so the PDI
> allocation is no longer done there.

Change is risky, especially when this touches platforms all the way to
CNL across at least 3 generations of Intel hardware since 2018, for no
tangible benefit.