Date:   Mon, 9 May 2022 15:32:33 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        vkoul@...nel.org
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        bard.liao@...el.com,
        Srinivasa Rao Mandadapu <quic_srivasam@...cinc.com>
Subject: Re: [PATCH v2] soundwire: qcom: adjust autoenumeration timeout



On 09/05/2022 15:24, Pierre-Louis Bossart wrote:
> 
>>>> You could say why do we need wait itself in the first place.
>>>>
>>>> The reason we need wait in first place is because, there is a danger of
>>>> codec accessing registers even before enumeration is finished. Because
>>>> most of the ASoC codec registration happens as part of codec/component
>>>> driver probe function rather than status callback.
>>>>
>>>> I hope this answers your questions.
>>>
>>>
>>> Humm, not really.
>>>
>>> First, you're using this TIMEOUT_MS value in 3 unrelated places, and
>>> using 2 different struct completion, which means there are side effects
>>> beyond autoenumeration.
>>
>> 2 of these 3 are autoenum ones, one is in probe path and other in bus
>> reset path during pm.
>>
>> The final one is broadcast timeout, new timeout value should be okay for
>> that too, given that we need 10ms timeout.
> 
> probably better to make things explicit with a different timeout value
> for the broadcast case.
I agree, we should define a dedicated 10ms timeout for this to avoid 
confusion.

> 
> 100ms for a broadcast is really eons, it's supposed to be immediate really.
> 
>>> And then I don't get what you do on a timeout. in the enumeration part,
>>
>> We can't do much on the timeout.
>>
>>> the timeout value is not checked for, so I guess enumeration proceeds
>>> without the hardware being available? That seems to contradict the
>>> assertion that you don't want to access registers before the hardware is
>>> properly initialized.
>>
>> Even if enumeration timeout, we will not access the registers because
>> the ASoC codec is not registered yet from WCD938x component master.
> 
> What happens when the codec is registered then? the autoenumeration
Codec is only registered after reset and when both TX and RX components 
are probed.

> still didn't complete, so what prevents the read/writes from failing then?
If codec is reset and registered and for some reason autoenum took more 
than 100ms which will be hw bug then :-).
In this case register read/writes will fail.

--srini
> 
>>> And then on broadcast you have this error handling:
>>>
>>>          ret = wait_for_completion_timeout(&swrm->broadcast,
>>>                            msecs_to_jiffies(TIMEOUT_MS));
>>>          if (!ret)
>>>              ret = SDW_CMD_IGNORED;
>>>          else
>>>              ret = SDW_CMD_OK;
>>>
>>> Which is equally confusing since SDW_CMD_IGNORED is really an error, and
>>> the bus layer does not really handle it well - not to mention that I
>>> vaguely recall the qcom hardware having its own definition of IGNORED?
>> QCom hardware alteast the version based on which this driver was written
>> did not have any support to report errors type back on register
>> read/writes.
>>
>> In this case a broad cast read or write did not generate a complete
>> interrupt its assumed that its ignored, as there is no way to say if its
>> error or ignored.
> 
> ok, that should be fine.
> 
> The code in bus.c mostly ignores -ENODATA for the suspend cases. For the
> bank switch, I forgot that we also ignore it, Bard added a patch in
> 2021. The only case where we abort a transfer is on a real error.
> 
> 
> 

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