+ * wake up master and slave so that slave can notify master
+ * the wakeen event and let codec driver check codec status
+ */
+ list_for_each_entry(slave, &bus->slaves, node) {
+ /*
+ * discard devices that are defined in ACPI tables but
+ * not physically present and devices that cannot
+ * generate wakes
+ */
+ if (slave->dev_num_sticky && slave->prop.wake_capable)
+ pm_request_resume(&slave->dev);
Hmmm, shouldn't slave do this? would it not make sense to notify the
slave thru callback and then slave decides to resume or not..?
In this mode, the bus is clock-stop mode, and events are detected with level
detector tied to PCI events. The master and slave devices are all in
pm_runtime suspended states. The codec cannot make any decisions on its own
since the bus is stopped, it needs to first resume, which assumes that the
master resumes first and the enumeration re-done before it can access any of
its registers.
By looping through the list of devices that can generate events, you end-up
first forcing the master to resume, and then each slave resumes and can
check who generated the event and what happened while suspended. if the
codec didn't generate the event it will go back to suspended mode after the
usual timeout.
We can add a callback but that callback would only be used for Intel
solutions, but internally it would only do a pm_request_resume() since the
codec cannot make any decisions before first resuming. In other words, it
would be an Intel-specific callback that is implemented using generic resume
operations. It's probably better to keep this in Intel-specific code, no?
I do not like the idea that a device would be woken up, that kind of
defeats the whole idea behind the runtime pm. Waking up a device to
check the events is a generic sdw concept, I don't see that as Intel
specific one.
In this case, this in an Intel-specific mode that's beyond what MIPI
defined. This is not the traditional in-band SoundWire wake defined in
the SoundWire specification. The bus is completely down, the master IP
is powered-off and all context lost. There is still the ability for a
Slave device to throw a wake as defined by MIPI in clock-stop-mode1, but
this is handled with a separate level detector and the wake detection is
handled by the PCI subsystem. On a wake, the master IP needs to be
powered-up, the entire bus needs to be restarted and the Slave devices
re-enumerated.
We trigger that sequence with a loop that calls pm_request_resume() for
all Slave devices that are present and exposed in their properties that
they are wake-capable. As you rightly said in your comments, this will
result a nice wake-up handled by the pm_runtime framework in the right
sequence (DSP first, then SoundWire master then Slave devices).
You will see in follow-up patches that the master IP can be configured
in different clock stop modes, depending on the needs (power/latency
compromise typically). When the more traditional SoundWire wake is used,
we do not use this sequence at all.
I would like to see a generic callback for the devices and let devices
do the resume part, that is standard operating principle when we deal
with suspended devices. If the device thinks they need to resume, they
will do the runtime resume, check the status and sleep if not
applicable. Since we have set the parents correctly, any resume
operation for slaves would wake master up as well...
I do not see a need for intel driver to resume slave devices here, or
did I miss something?
Yes, the part "If the device thinks they need to resume" is not quite
right. The Slave device cannot access its registers before fully
resuming, which in this case means a re-enumeration, so cannot "think"
or make a decision on its own. That's the reason why we force them to
resume, since it's the first step they would need to do anyways, and
then if they don't have anything to do they go back to idle after a
timeout. I invite you to see the suspend/resume sequences in codec
drivers where you will see regmap access moves to cache-only on suspend
and full access restored on resume, along with a hardware sync.
I see your point and I really think we are talking about a similar
sequence, but we simplified your idea since there's no possibility of
making a decision before Slave devices resume.
The only optimization we did here is that we only resume Slave devices
than can generate a wake, and filter out the 'ghost' devices that are
described in ACPI tables but don't physically exist.
Does this help?
