Re: [PATCH] soundwire: intel: trap TRIGGER_SUSPEND in .trigger callback

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 8/6/21 8:37 AM, Vinod Koul wrote:
> On 02-08-21, 10:46, Pierre-Louis Bossart wrote:
>>
>>>>>>>> The trigger callback is handled in the stream lock atomically,
>>>>>>>> and are you sure that you want to operate a possibly heavy task there?
>>>>>>>
>>>>>>> It's a good objection that we didn't think of.
>>>>>>
>>>>>> Doesn't Intel use non atomic trigger to send IPCs which anyway
>>>>>> involve code which can sleep..?
>>>>>
>>>>> sof_sdw.c doesn't seem setting it?
>>>>
>>>> Yes I think init_dai_link() should set it. Maybe Pierre/Bard would know why.
>>>
>>> init_dai_link() is to assign dai link elements only. No IPC is needed.
>>
>> The 'nonatomic' concept is only used for an FE dailink which expose a
>> PCM device:
>>
>> soc-pcm.c:	pcm->nonatomic = rtd->dai_link->nonatomic;
>>
>> Setting a BE dailink as 'nonatomic' would not accomplish much since BEs
>> use the 'no_pcm' option.
> 
> are no_pcm & nonatomic supposed to be not used together? So if FE is
> nonatomic would BE trigger be atomic or nonatomic?

I don't follow the multiple negations, so let me retry:

For Intel machine drivers, all BE dailinks use
.no_pcm = 1 (explicit setting)
.nonatomic = 0 (implicit).

All FE dailinks use
.no_pcm = 0 (implicit)
.nonatomic = 1 (explicit setting)

>> So the question is: is there any issue with sending an IPC in a DAI
>> trigger callback?
> 
> Sorry looks like we diverged, orignal question was can we do heavy tasks
> in trigger, the answer is no, unless one uses nonatomic flag which was
> added so that people can do that work with DSPs like sending IPCs..
> Maybe we should add heavy slimbus/soundwire handling to it too...?

I don't think the answer is as clear as you describe it Vinod.

The .nonatomic field is at the BE dailink level.

Unless I am missing something, I don't see anything that lets me set a
.nonatomic property at the *DAI* level.

The other problem is to define 'heavy task'. In this case, we are
sending an IPC indeed, but the response is immediate, typically in the
next ms tick.

IOW, if the response time is in the ms order of magnitude, is this 'heavy'?

>> This is not very different from sending a command on a
>> bus btw, I see a similar example for SLIMbus devices:
>>
>> wcd9335.c:      case SNDRV_PCM_TRIGGER_SUSPEND:
>> wcd9335.c-      case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
>> wcd9335.c-              slim_stream_unprepare(dai_data->sruntime);
>> wcd9335.c-              slim_stream_disable(dai_data->sruntime);
>>
>> int slim_stream_unprepare(struct slim_stream_runtime *stream)
>> {
>> 	int i;
>>
>> 	for (i = 0; i < stream->num_ports; i++)
>> 		slim_disconnect_port(stream, &stream->ports[i]);
>>
>> static int slim_disconnect_port(struct slim_stream_runtime *stream,
>> 				struct slim_port *port)
>> {
>> 	struct slim_device *sdev = stream->dev;
>> 	u8 wbuf[1];
>> 	struct slim_val_inf msg = {0, 1, NULL, wbuf, NULL};
>> 	u8 mc = SLIM_MSG_MC_DISCONNECT_PORT;
>> 	DEFINE_SLIM_LDEST_TXN(txn, mc, 5, stream->dev->laddr, &msg);
>>
>> 	wbuf[0] = port->id;
>> 	port->ch.state = SLIM_CH_STATE_DISCONNECTED;
>> 	port->state = SLIM_PORT_DISCONNECTED;
>>
>> 	return slim_do_transfer(sdev->ctrl, &txn);
>> }
>>
>> Such commands may take time...
> 
> Agree, so users should be recommended to use nonatomic triggers.

The SLIMbus example relies on DAIs as well, and this option does not
exist, does it?