kselftest: alsa: Add simplistic test for ALSA mixer controls kselftest

Add a basic test for the mixer control interface. For every control on
every sound card in the system it checks that it can read and write the
default value where the control supports that and for writeable controls
attempts to write all valid values, restoring the default values after
each test to minimise disruption for users.

There are quite a few areas for improvement - currently no coverage of the
generation of notifications, several of the control types don't have any
coverage for the values and we don't have any testing of error handling
when we attempt to write out of range values - but this provides some basic
coverage.

This is added as a kselftest since unlike other ALSA test programs it does
not require either physical setup of the device or interactive monitoring
by users and kselftest is one of the test suites that is frequently run by
people doing general automated testing so should increase coverage. It is
written in terms of alsa-lib since tinyalsa is not generally packaged for
distributions which makes things harder for general users interested in
kselftest as a whole but it will be a barrier to people with Android.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20211210185410.740009-2-broonie@kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>

MAINTAINERS

@@ -17805,6 +17805,7 @@ F:	Documentation/sound/
 F:	include/sound/
 F:	include/uapi/sound/
 F:	sound/
+F:	tools/testing/selftests/alsa
 
 SOUND - COMPRESSED AUDIO
 M:	Vinod Koul <vkoul@kernel.org>
@@ -17824,6 +17825,13 @@ F:	include/sound/dmaengine_pcm.h
 F:	sound/core/pcm_dmaengine.c
 F:	sound/soc/soc-generic-dmaengine-pcm.c
 
+SOUND - ALSA SELFTESTS
+M:	Mark Brown <broonie@kernel.org>
+L:	alsa-devel@alsa-project.org (moderated for non-subscribers)
+L:	linux-kselftest@vger.kernel.org
+S:	Supported
+F:	tools/testing/selftests/alsa
+
 SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEMENT (ASoC)
 M:	Liam Girdwood <lgirdwood@gmail.com>
 M:	Mark Brown <broonie@kernel.org>

tools/testing/selftests/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
-TARGETS = arm64
+TARGETS += alsa
+TARGETS += arm64
 TARGETS += bpf
 TARGETS += breakpoints
 TARGETS += capabilities

tools/testing/selftests/alsa/.gitignore

@@ -0,0 +1 @@
+mixer-test

tools/testing/selftests/alsa/Makefile

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+
+CFLAGS += $(shell pkg-config --cflags alsa)
+LDLIBS += $(shell pkg-config --libs alsa)
+
+TEST_GEN_PROGS := mixer-test
+
+include ../lib.mk