Re: [PATCH v2 4/6] soundwire: Handle multiple master instances in a stream

[Shreyas NC <shreyas.nc@intel.com>]

> >>>+
> >>>+		/* Bank switch */
> >>>+		ret = sdw_bank_switch(bus);
> >>>  		if (ret < 0) {
> >>>-			dev_err(bus->dev, "Pre bank switch op failed: %d", ret);
> >>>+			dev_err(bus->dev, "Bank switch failed: %d", ret);
> >>>  			return ret;
> >>>  		}
> >>You probably want to add a comment that in multi-link operation the actual
> >>bank_switch happens later and is done in a synchronized manner. This is lost
> >>if you just move code around and move the bank_switch into a loop.
> >>
> >>I am actually no longer clear just looking at this code on when the
> >>bank_switch happens (i know we've discussed this before but I am trying to
> >>find out just based on this v2 instead of projecting how I think it should
> >>work):
> >>In Patch 6/6 it's pretty obvious that the bank switch happens when the
> >>SyncGO bit is set, but there is no comment or explanation on how we reach
> >>the intel_post_bank_switch() routine once for all masters handling a stream
> >>when everything is based on loops. Clearly the intel_pre_bank_switch is
> >>called multiple times (once per master), I guess I am missing what the
> >>trigger is for the intel_post_bank_switch() routine to be invoked?
> >>
> >
> >Hi Pierre,
> >
> >To answer your last question, do_bank_switch is where we perform all the
> >bank switch operations.
> >
> >In first loop for Master(s) involved in stream, ops->pre_bank_switch and
> >bank_switch is performed. In 2nd loop for Master(s) involved in stream,
> >ops->post_bank_switch and wait for bank switch is performed.
> >
> >Assuming a stream with Master 1 and Master 2, the go_sync bit will be
> >set in Master 1 intel_post_bank_switch call which will trigger bank
> >switch for both the Master's. The Master 2 intel_post_bank_switch call
> >will just return as it will won't see CMDSYNC bit set for any Master(s).
> 
> Makes sense, thanks for taking the time to provide the details I didn't
> remember.
> Sreyas, if you could add a bit of information on this it'd be a good thing -
> specifically the expectation is that the bank switch is triggered by the
> first master in the master_list loop while others just return without doing
> anything.
> 

Sure, makes sense. I will add these details in the relevant patch.

--Shreyas

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