Kernel dump (WARN_ON) ocurred during system boot-up inside regmap_write():

------------[ cut here ]------------
WARNING: CPU: 0 PID: 47 at kernel/locking/lockdep.c:2744 lockdep_trace_alloc+0xe8/0x108()
DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
Modules linked in:
CPU: 0 PID: 47 Comm: kworker/u2:2 Not tainted 3.18.0-rc1-10245-gb75d289-dirty #56
Workqueue: deferwq deferred_probe_work_func
Backtrace:
[<80012294>] (dump_backtrace) from [<80012578>] (show_stack+0x18/0x1c)
 r6:8097c73c r5:8097c73c r4:00000000 r3:be33ba80
[<80012560>] (show_stack) from [<806aac48>] (dump_stack+0x8c/0xa4)
[<806aabbc>] (dump_stack) from [<8002a694>] (warn_slowpath_common+0x70/0x94)
 r6:80062838 r5:00000009 r4:bd827b30 r3:be33ba80
[<8002a624>] (warn_slowpath_common) from [<8002a6f0>] (warn_slowpath_fmt+0x38/0x40)
 r8:00000004 r7:00000001 r6:000080d0 r5:60000193 r4:bd826010
[<8002a6bc>] (warn_slowpath_fmt) from [<80062838>] (lockdep_trace_alloc+0xe8/0x108)
 r3:80831590 r2:8082e160
[<80062750>] (lockdep_trace_alloc) from [<800ea5dc>] (kmem_cache_alloc+0x28/0x134)
 r5:000080d0 r4:be001f00
[<800ea5b4>] (kmem_cache_alloc) from [<8038d72c>] (regcache_rbtree_write+0x15c/0x648)
 r10:00000000 r9:0000001c r8:00000004 r7:00000001 r6:00000000 r5:bd819a00
 r4:00000000 r3:811aea88
[<8038d5d0>] (regcache_rbtree_write) from [<8038c4d8>] (regcache_write+0x5c/0x64)
 r10:be3f9f88 r9:00000000 r8:00000004 r7:00000001 r6:00000000 r5:00000001
 r4:bd819a00
[<8038c47c>] (regcache_write) from [<8038b0dc>] (_regmap_raw_write+0x134/0x5f4)
 r6:be3f9f84 r5:00000001 r4:bd819a00 r3:00000001
[<8038afa8>] (_regmap_raw_write) from [<8038b610>] (_regmap_bus_raw_write+0x74/0x94)
 r10:00000000 r9:00000001 r8:be3fb080 r7:bd819a00 r6:00000001 r5:00000000
 r4:bd819a00
[<8038b59c>] (_regmap_bus_raw_write) from [<8038a8b4>] (_regmap_write+0x60/0x9c)
 r6:00000001 r5:00000000 r4:bd819a00 r3:8038b59c
[<8038a854>] (_regmap_write) from [<8038ba24>] (regmap_write+0x48/0x68)
 r7:bd81ad80 r6:00000001 r5:00000000 r4:bd819a00
[<8038b9dc>] (regmap_write) from [<80528f30>] (fsl_asrc_dai_probe+0x34/0x104)
 r6:bd888628 r5:be3fb080 r4:be3b4410 r3:be3b442c
------------[ dump end ]------------

=============================================================================
2741         /*
2742          * Oi! Can't be having __GFP_FS allocations with IRQs disabled.
2743          */
2744         if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)))
2745                 return;
=============================================================================

By looking at 2744 line, we can get that it's because regcache_rbtree_write()
would call kmalloc() with GFP flag if it couldn't find an existing block to
insert nodes while this kmalloc() call is inside a spin_lock_irq_save pair,
i.e. IRQs disabled.

Even though this may be a bug that should be fixed, I still try to send this
patch as a quick fix (work around) since it does no harm to assign default
values of every registers when using regcache.
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>