class SetElementState

Controls the processing element specified by `processing_element_id`, a unique ElementId

returned by `GetElements`.

The `state` specified in calls to `SetElementState` is a `SettableElementState`. This is a

subset of `ElementState` because some fields returned by `WatchElementState` (e.g. `latency`

or `plug_state`) can only be observed (not set) by the client.

Returns `ZX_ERR_INVALID_ARGS` if `processing_element_id` does not match a known ElementId

returned by `GetElements`, or if `state` is not valid for the element. This entails any

violation of the rules specified in this protocol.

Examples:

`state` specifies that an element should be stopped or bypassed, but the corresponding

element does not specify (or explicitly set to false) `can_stop` or `can_bypass`.

`state` includes a `type_specific` entry, but that `SettableTypeSpecificElementState` does

not match the `ElementType` of the element corresponding to `processing_element_id`.

`state` changes an `EqualizerBandState` for an `EQUALIZER` element (so far so good), but

specifies a change to `frequency` when this element did not set `CAN_CONTROL_FREQUENCY`

in its `supported_controls`.

`state` specifies a `GainElementState` for a `GAIN` element with a `gain` value that is

-infinity, NAN, or outside the Element's stated [`min_gain`, `max_gain`] range.

Callers may intersperse method calls to the `SignalProcessing` protocol with calls to other

driver protocols. Some non-`SignalProcessing` configuration changes may require a

renegotiation of the driver state before certain elements can receive a `SetElementState`.

For example, if a `DaiFormat` is changed, then `SetElementState` changing an `AGL` element's

parameters may not require renegotiation of driver state because changing gain parameters

usually does not change the set of supported audio formats.

By contrast, following the same `DaiFormat` change, before `SetElementState` can be called

on a `CONNECTION_POINT` element, the driver state may need to be reestablished because the

format change may invalidate the set of supported formats returned in a previous

`GetDaiFormats` protocol call for another part of the Topology.

It is the driver's job to determine when renegotiation is required. When this is needed,

the related `SetElementState` call must return `ZX_ERR_BAD_STATE` and the client must

close the protocol channel entirely, such that the protocol negotiations are started over.

The client then must re-invoke the `SetElementState` call that returned

`ZX_ERR_BAD_STATE` before any non-`SignalProcessing` protocol calls.