linux-kernel - Re: [RFC PATCH 1/2] soundwire: add support for static port mapping

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Message-ID: <3ee60ad9-9635-649e-ba67-d40a96b25256@linux.intel.com>
Date:   Thu, 21 Jan 2021 12:00:43 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        vkoul@...nel.org, yung-chuan.liao@...ux.intel.com
Cc:     gregkh@...uxfoundation.org, sanyog.r.kale@...el.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] soundwire: add support for static port mapping

On 1/21/21 9:41 AM, Srinivas Kandagatla wrote:
> 
> 
> On 21/01/2021 14:56, Pierre-Louis Bossart wrote:
>>
>>
>>> Port allocations are something like this:
>>>
>>> RX: (Simple)
>>> Port 1 -> HPH L/R
>>> Port 2 -> CLASS H Amp
>>> Port 3 -> COMP
>>> Port 4 -> DSD.
>>>
>>> TX: (This get bit more complicated)
>>> Port 1: PCM
>>> Port 2: ADC 1 & 2
>>> Port 3: ADC 3 & 4
>>> Port 4: DMIC-0, DMIC-1, DIMC-2 , DMIC-3 and MBHC
>>> Port 5: DMIC-4, DMIC-5, DMIC-6 and DMIC-7
>>>
>>> We handle the port allocation dynamically based on mixer and dapm 
>>> widgets in my code! Also channel allocations are different for each 
>>> function!
>>
>> Sorry, I am not following here. What is dynamic here and use-case 
>> dependent? And is this a mapping on the master or the codec sides that 
>> you want to modify?
> 
> [SLAVE]-------[MASTER]
> NA-------------Port 1: PCM
> Port 1---------Port 2: ADC 1 & 2
> Port 2---------Port 3: ADC 3 & 4
> Port 3---------Port 4: DMIC-0, DMIC-1, DIMC-2 , DMIC-3 and MBHC
> Port 4---------Port 5: DMIC-4, DMIC-5, DMIC-6 and DMIC-7
> 
> 
> Mapping is still static however Number of ports selection and channel 
> mask will be dynamic here.
> 
> 
> Example: for Headset MIC usecase we will be using Slv Port1, Slv Port3 
> along with Mstr Port2 and Master Port4
> 
> Similarly for usecases like Digital MIC or other Analog MICs.

Sorry, I must be thick here, but in my experience the choice of Digital 
or analog mics is a hardware design level not a use-case one. Using ADC 
1 & 2 at the same time as DMICs is very surprising to me. You'd have 
different sensitivities/performance, not sure how you would combine the 
results.

I also don't see how a headset mic can both use Analog and digital, 
unless we have a different definition of what a 'headset' is.

>>>> Does this help and can you align on what Intel started with?
>>>
>>> Firstly, This is where the issue comes, if we go with the 
>>> suggested(dai->id) solution, we would end up with a long list of 
>>> dai-links with different combinations of both inputs/output 
>>> connections and usecases. Again we have to deal with limited DSP 
>>> resources too!
>>>
>>> Secondly, The check [1] in stream.c will not allow more than one 
>>> master port config to be added to master runtime. Ex: RX Port 1, 2, 3 
>>> is used for Headset Playback.
>>
>> I am confused here, we do have examples in existing codec drivers 
>> where we use multiple ports for a single stream, e.g. for IV feedback 
>> we use 2 ports.
> 
> Is this on multi_link? which is why it might be working for you.

no, this is done at the codec driver level, which has no notion of 
multi-link. we pass a port_config as a array of 2.

> Currently we have below check in sdw_stream_add_master().
> 
> if (!bus->multi_link && stream->m_rt_count > 0) {
>      dev_err(bus->dev, "Multilink not supported, link %d\n", bus->link_id);
>      ret = -EINVAL;
>      goto unlock;
> }
> 
> If we have single master(like my case) and dai-links which have more 
> then one port  will be calling  sdw_stream_add_master() for each port, 
> so m_rt_count above check will fail for the second call!

if you use multiple ports in a given master for the same stream, you 
should have the m_rt_count == 1. That's a feature, not a bug.

A port is not a stream... You cannot call sdw_stream_add_master() for 
each port, that's not what the concept was. You allocate ONE master_rt 
per master, and that master_rt deals with one or more ports - your choice.

A 'stream' is an abstract data transport which can be split across 
multiple masters/sales and for each master/slave use multiple ports.
When calling sdw_stream_add_master/slave, you need to provide a 
port_config/num_ports to state which ports will be used on that 
master/slave when using the stream. That's how we e.g. deal with 4ch 
streams that are handled by two ports on each side.

To up-level a bit, the notion of 'stream' is actually very very similar 
to the notion of dailink. And in fact, the 'stream' is actually created 
for Intel in the dailink .startup callback, so I am quite in the dark on 
what you are trying to accomplish.