[PATCH 5/6] soundwire: qcom: update register read/write routine
Pierre-Louis Bossart
pierre-louis.bossart at linux.intel.com
Mon Feb 1 17:42:49 CET 2021
On 2/1/21 9:50 AM, Srinivas Kandagatla wrote:
>
>
> On 29/01/2021 19:33, Pierre-Louis Bossart wrote:
>>
>>
>> On 1/29/21 11:32 AM, Srinivas Kandagatla wrote:
>>> In the existing code every soundwire register read and register write
>>> are kinda blocked. Each of these are using a special command id that
>>
>> what does 'kinda blocked' mean?
>
> I meant read/writes are waiting for completion interrupt!
>
>>
>>> 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.
>
>
>>
>>> + if (id != SWR_BROADCAST_CMD_ID) {
>>> + if (id < 14)
>>> + id += 1;
>>> + else
>>> + id = 0;
>>
>> that is really odd. if id=13 (group2) then id becomes 14 (master
>> address). A comment is really needed here.
>
> This is magic value for each fifo read or write, so that we can verify
> that them by comparing with this magic value!
>
> This has nothing to do with device number!
You should probably add a comment here then, or use a #define instead of
the 14 which threw me off.
>
>>
>>> + if (cmd_id == SWR_BROADCAST_CMD_ID) {
>>> + /*
>>> + * sleep for 10ms for MSM soundwire variant to allow broadcast
>>> + * command to complete.
>>
>> that's also super-odd. There is nothing in SoundWire that makes any
>> difference between a regular and a broadcast command. they all
>> complete in the same time (a frame).
>>> + */
>>> + ret = wait_for_completion_timeout(&swrm->broadcast, (2 *
>>> HZ/10));
>>
>> is this 10ms really or dependent on CONFIG_HZ?
comment missed?
>>
>>> + if (!ret)
>>> + ret = SDW_CMD_IGNORED;
>>> + else
>>> + ret = SDW_CMD_OK;
>>
>> no CMD_FAILED support?
>
> Qcom controllers does not provide that information if the command is
> ignored or failed by any means!
>
> That was the behavior from the starting of this driver.
ah yes, now I remember this.
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