kselftest: alsa: Check for event generation when we write to controls

Add some coverage of event generation to mixer-test. Rather than doing a
separate set of writes designed to trigger events we add a step to the
existing write_and_verify() which checks to see if the value we read back
from non-volatile controls matches the value before writing and that an
event is or isn't generated as appropriate. The "tests" for events then
simply check that no spurious or missing events were detected. This avoids
needing further logic to generate appropriate values for each control type
and maximises coverage.

When checking for events we use a timeout of 0. This relies on the kernel
generating any event prior to returning to userspace when setting a control.
That is currently the case and it is difficult to see it changing, if it
does the test will need to be updated. Using a delay of 0 means that we
don't slow things down unduly when checking for no event or when events
fail to be generated.

We don't check behaviour for volatile controls since we can't tell what
the behaviour is supposed to be for any given control.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220202150902.19563-1-broonie@kernel.org


Signed-off-by: Takashi Iwai <tiwai@suse.de>