[PATCH 5/6] soundwire: qcom: update register read/write routine

[Pierre-Louis Bossart]

>>>>> generates interrupt after it successfully finishes. This is really
>>>>> overhead, limiting and not really necessary unless we are doing
>>>>> something special.
>>>>>
>>>>> We can simply read/write the fifo that should also give exactly
>>>>> what we need! This will also allow to read/write registers in
>>>>> interrupt context, which was not possible with the special
>>>>> command approach.
>>>>
>>>> This is really unclear, sorry.
>>>
>>> If read/writes are waiting for an interrupt, it becomes difficult to 
>>> read or write to any registers from same interrupt handler!
>>
>> Well, yes, you need to handle the complete() at a lower level than the 
>> code that initiates the transactions otherwise you self-deadlock.
>>
>> IIRC in the Intel initial code, the complete was in the handler and 
>> the register IOs in the thread.
>>
> Yes, we did the same in previous version of the code, however with this 
> patch reading/writing fifo directly without need of completion should 
> remove that need of another thread!

Right, but you'll also write-off some command/control efficiency by 
either sleeping too much before checking the status, or sleeping too 
little and reading status from a transaction that's not finished.