[RFC PATCH] regulator: Fix recursive mutex lockdep warning

[Srinivas Kandagatla]

A recursive lockdep warning occurs if you call regulator_set_voltage()
on a load switches that are modelled as regulators with a parent supply as
there is no nesting annotation for the rdev->mutex.
To avoid this warning, use the unlocked version of the get_voltage().

wiithout this patch kernel throws up below warning:

 =============================================
 [ INFO: possible recursive locking detected ]
 4.2.0-rc5-dirty #132 Not tainted
 ---------------------------------------------
 swapper/0/1 is trying to acquire lock:
  (&rdev->mutex){+.+.+.}, at: [<c066b6e4>] regulator_get_voltage+0x44/0x68

 but task is already holding lock:
  (&rdev->mutex){+.+.+.}, at: [<c066d718>] regulator_set_voltage+0x50/0x168

 other info that might help us debug this:
  Possible unsafe locking scenario:

 CPU0
 ----
   lock(&rdev->mutex);
   lock(&rdev->mutex);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

 3 locks held by swapper/0/1:
 #0:  (&dev->mutex){......}, at: [<c0756e34>] __driver_attach+0x58/0xa8
 #1:  (&dev->mutex){......}, at: [<c0756e44>] __driver_attach+0x68/0xa8
 #2:  (&rdev->mutex){+.+.+.}, at: [<c066d718>] regulator_set_voltage+0x50/0x168

 stack backtrace:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc5-dirty #132
 Hardware name: Qualcomm (Flattened Device Tree)
 [<c021af98>] (unwind_backtrace) from [<c021536c>] (show_stack+0x20/0x24)
 [<c021536c>] (show_stack) from [<c0ba6698>] (dump_stack+0x8c/0xc0)
 [<c0ba6698>] (dump_stack) from [<c02a8604>] (__lock_acquire+0x1bf4/0x1ec0)
 [<c02a8604>] (__lock_acquire) from [<c02a9020>] (lock_acquire+0xe0/0x300)
 [<c02a9020>] (lock_acquire) from [<c0baa7dc>] (mutex_lock_nested+0x88/0x45c)
 [<c0baa7dc>] (mutex_lock_nested) from [<c066b6e4>] (regulator_get_voltage+0x44/0x68)
 [<c066b6e4>] (regulator_get_voltage) from [<c066b5c8>] (_regulator_get_voltage+0xb8/0x190)
 [<c066b5c8>] (_regulator_get_voltage) from [<c066d7f4>] (regulator_set_voltage+0x12c/0x168)
 [<c066d7f4>] (regulator_set_voltage) from [<c09af5b4>] (mmci_sig_volt_switch+0x6c/0x110)
 [<c09af5b4>] (mmci_sig_volt_switch) from [<c099d8a4>] (mmc_power_up+0x78/0x114)
 [<c099d8a4>] (mmc_power_up) from [<c099e69c>] (mmc_start_host+0x54/0x7c)
 [<c099e69c>] (mmc_start_host) from [<c099f95c>] (mmc_add_host+0x6c/0x90)
 [<c099f95c>] (mmc_add_host) from [<c09b014c>] (mmci_probe+0x5ac/0x854)
 [<c09b014c>] (mmci_probe) from [<c063f5e4>] (amba_probe+0xdc/0x158)
 [<c063f5e4>] (amba_probe) from [<c0756d38>] (driver_probe_device+0x1dc/0x280)
 [<c0756d38>] (driver_probe_device) from [<c0756e80>] (__driver_attach+0xa4/0xa8)
 [<c0756e80>] (__driver_attach) from [<c0755120>] (bus_for_each_dev+0x64/0x98)
 [<c0755120>] (bus_for_each_dev) from [<c0756608>] (driver_attach+0x2c/0x30)
 [<c0756608>] (driver_attach) from [<c075634c>] (bus_add_driver+0xf8/0x204)
 [<c075634c>] (bus_add_driver) from [<c0757fb8>] (driver_register+0x88/0x104)
 [<c0757fb8>] (driver_register) from [<c063f418>] (amba_driver_register+0x50/0x64)
 [<c063f418>] (amba_driver_register) from [<c113e904>] (mmci_driver_init+0x14/0x1c)
 [<c113e904>] (mmci_driver_init) from [<c020adb4>] (do_one_initcall+0x90/0x1e4)
 [<c020adb4>] (do_one_initcall) from [<c10e4ea8>] (kernel_init_freeable+0x12c/0x1f4)
 [<c10e4ea8>] (kernel_init_freeable) from [<c0b9ec78>] (kernel_init+0x1c/0xfc)
 [<c0b9ec78>] (kernel_init) from [<c02114d8>] (ret_from_fork+0x14/0x3c)

Reported-by: Nicolas Dechesne <nicolas.dechesne@xxxxxxxxxx>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
---
 drivers/regulator/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 3c3137a..7717b04 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2919,7 +2919,7 @@ static int _regulator_get_voltage(struct regulator_dev *rdev)
 	} else if (rdev->desc->fixed_uV && (rdev->desc->n_voltages == 1)) {
 		ret = rdev->desc->fixed_uV;
 	} else if (rdev->supply) {
-		ret = regulator_get_voltage(rdev->supply);
+		ret = _regulator_get_voltage(rdev->supply->rdev);
 	} else {
 		return -EINVAL;
 	}
-- 
1.9.1

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