Re: [PATCH v2] soundwire: qcom: adjust autoenumeration timeout

[Srinivas Kandagatla]

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.