ASoC: max98090: silence lockdep warning

Commit 08df0d9a ("ASoC: max98090: revert "ASoC: max98090: fix lockdep
warning"") provided a good rationale for removing separate lock for the
SHDN register access. However it restored the lockdep warning during the
system boot. To silence the lockdep warning, mark the mutex taken in the
max98090_shdn_save() function with the lockdep class dedicated for the
runtime DAPM operations: SND_SOC_DAPM_CLASS_RUNTIME. This finally fixes
the following lockdep warning observed on Exynos4412-based Odroid U3
board:

======================================================
WARNING: possible circular locking dependency detected
5.5.0-rc7-next-20200123 #7329 Not tainted
------------------------------------------------------
alsactl/1105 is trying to acquire lock:
ed4f7cf4 (&card->dapm_mutex){+.+.}, at: max98090_shdn_save+0x1c/0x28

but task is already holding lock:
edb8d49c (&card->controls_rwsem){++++}, at: snd_ctl_ioctl+0xcc/0xbb8

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&card->controls_rwsem){++++}:
       snd_ctl_add_replace+0x3c/0x84
       dapm_create_or_share_kcontrol+0x24c/0x2e0
       snd_soc_dapm_new_widgets+0x308/0x594
       snd_soc_bind_card+0x834/0xa94
       devm_snd_soc_register_card+0x34/0x6c
       odroid_audio_probe+0x288/0x34c
       platform_drv_probe+0x6c/0xa4
       really_probe+0x200/0x48c
       driver_probe_device+0x78/0x1f8
       bus_for_each_drv+0x74/0xb8
       __device_attach+0xd4/0x16c
       bus_probe_device+0x88/0x90
       deferred_probe_work_func+0x3c/0xd0
       process_one_work+0x230/0x7bc
       worker_thread+0x44/0x524
       kthread+0x130/0x164
       ret_from_fork+0x14/0x20
       0x0

-> #0 (&card->dapm_mutex){+.+.}:
       lock_acquire+0xe8/0x270
       __mutex_lock+0x9c/0xb18
       mutex_lock_nested+0x1c/0x24
       max98090_shdn_save+0x1c/0x28
       max98090_put_enum_double+0x20/0x40
       snd_ctl_ioctl+0x190/0xbb8
       ksys_ioctl+0x484/0xb10
       ret_fast_syscall+0x0/0x28
       0xbede0564

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&card->controls_rwsem);
                               lock(&card->dapm_mutex);
                               lock(&card->controls_rwsem);
  lock(&card->dapm_mutex);

 *** DEADLOCK ***

1 lock held by alsactl/1105:
 #0: edb8d49c (&card->controls_rwsem){++++}, at: snd_ctl_ioctl+0xcc/0xbb8

stack backtrace:
CPU: 2 PID: 1105 Comm: alsactl Not tainted 5.5.0-rc7-next-20200123 #7329
Hardware name: Samsung Exynos (Flattened Device Tree)
[<c01126f0>] (unwind_backtrace) from [<c010e1e8>] (show_stack+0x10/0x14)
[<c010e1e8>] (show_stack) from [<c0b5234c>] (dump_stack+0xb4/0xe0)
[<c0b5234c>] (dump_stack) from [<c018a610>] (check_noncircular+0x1ec/0x208)
[<c018a610>] (check_noncircular) from [<c018ca2c>] (__lock_acquire+0x1210/0x25ec)
[<c018ca2c>] (__lock_acquire) from [<c018e728>] (lock_acquire+0xe8/0x270)
[<c018e728>] (lock_acquire) from [<c0b71928>] (__mutex_lock+0x9c/0xb18)
[<c0b71928>] (__mutex_lock) from [<c0b723c0>] (mutex_lock_nested+0x1c/0x24)
[<c0b723c0>] (mutex_lock_nested) from [<c086097c>] (max98090_shdn_save+0x1c/0x28)
[<c086097c>] (max98090_shdn_save) from [<c08613f8>] (max98090_put_enum_double+0x20/0x40)
[<c08613f8>] (max98090_put_enum_double) from [<c0833f20>] (snd_ctl_ioctl+0x190/0xbb8)
[<c0833f20>] (snd_ctl_ioctl) from [<c02cae14>] (ksys_ioctl+0x484/0xb10)
[<c02cae14>] (ksys_ioctl) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xed331fa8 to 0xed331ff0)
...

Fixes: 08df0d9a ("ASoC: max98090: revert "ASoC: max98090: fix lockdep warning"")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20200123134046.9769-1-m.szyprowski@samsung.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/max98090.c

@@ -52,7 +52,8 @@ static void max98090_shdn_restore_locked(struct max98090_priv *max98090)
 
 static void max98090_shdn_save(struct max98090_priv *max98090)
 {
-	mutex_lock(&max98090->component->card->dapm_mutex);
+	mutex_lock_nested(&max98090->component->card->dapm_mutex,
+			  SND_SOC_DAPM_CLASS_RUNTIME);
 	max98090_shdn_save_locked(max98090);
 }