linux-kernel - Re: [PATCH v2] soundwire: qcom: adjust autoenumeration timeout

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Message-ID: <97cd6566-e686-e1f2-fe91-4b4ba9d95f12@linux.intel.com>
Date:   Mon, 9 May 2022 09:24:59 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        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


>>> 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.

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
still didn't complete, so what prevents the read/writes from failing then?

>> 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.