[media] rtl2832: implement own lock for regmap

Introduce own lock to silence lockdep warning. lockdep validator
makes wrong decision when two similar (&map->mutex) locks were taken
recursively, even those are different mutexes in a two different
drivers. After that patch, functionality remains same, but mutex names
are different. That is a temporary hack, proper solution is make
regmap aware of locked nested locking rules.

=============================================
[ INFO: possible recursive locking detected ]
3.18.0-rc4+ #4 Tainted: G O
---------------------------------------------
kdvb-ad-0-fe-0/2814 is trying to acquire lock:
(&map->mutex){+.+.+.}, at: [<ffffffff814ec90f>] regmap_lock_mutex+0x2f/0x40

but task is already holding lock:
(&map->mutex){+.+.+.}, at: [<ffffffff814ec90f>] regmap_lock_mutex+0x2f/0x40

other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&map->mutex);
lock(&map->mutex);

*** DEADLOCK ***
May be due to missing lock nesting notation
1 lock held by kdvb-ad-0-fe-0/2814:
#0: (&map->mutex){+.+.+.}, at: [<ffffffff814ec90f>] regmap_lock_mutex+0x2f/0x40

stack backtrace:
CPU: 3 PID: 2814 Comm: kdvb-ad-0-fe-0 Tainted: G O 3.18.0-rc4+ #4
Hardware name: System manufacturer System Product Name/M5A78L-M/USB3, BIOS 2001 09/11/2014
0000000000000000 00000000410c8772 ffff880293af3868 ffffffff817a6f82
0000000000000000 ffff8800b3462be0 ffff880293af3968 ffffffff810e7f94
ffff880293af3888 00000000410c8772 ffffffff82dfee60 ffffffff81ab8f89
Call Trace:
[<ffffffff817a6f82>] dump_stack+0x4e/0x68
[<ffffffff810e7f94>] __lock_acquire+0x1ea4/0x1f50
[<ffffffff810e2a7d>] ? trace_hardirqs_off+0xd/0x10
[<ffffffff817b01f3>] ? _raw_spin_lock_irqsave+0x83/0xa0
[<ffffffff810e13e6>] ? up+0x16/0x50
[<ffffffff810e2a7d>] ? trace_hardirqs_off+0xd/0x10
[<ffffffff817af8bf>] ? _raw_spin_unlock_irqrestore+0x5f/0x70
[<ffffffff810e9069>] lock_acquire+0xc9/0x170
[<ffffffff814ec90f>] ? regmap_lock_mutex+0x2f/0x40
[<ffffffff817ab50e>] mutex_lock_nested+0x7e/0x430
[<ffffffff814ec90f>] ? regmap_lock_mutex+0x2f/0x40
[<ffffffff814ec90f>] ? regmap_lock_mutex+0x2f/0x40
[<ffffffff817a530b>] ? printk+0x70/0x86
[<ffffffff8110d9e8>] ? mod_timer+0x168/0x240
[<ffffffff814ec90f>] regmap_lock_mutex+0x2f/0x40
[<ffffffff814f08d9>] regmap_update_bits+0x29/0x60
[<ffffffffa03e9778>] rtl2832_select+0x38/0x70 [rtl2832]
[<ffffffffa039b03d>] i2c_mux_master_xfer+0x3d/0x90 [i2c_mux]
[<ffffffff815da493>] __i2c_transfer+0x73/0x2e0
[<ffffffff815dbaba>] i2c_transfer+0x5a/0xc0
[<ffffffff815dbb6e>] i2c_master_send+0x4e/0x70
[<ffffffffa03ff25a>] regmap_i2c_write+0x1a/0x50 [regmap_i2c]
[<ffffffff817ab713>] ? mutex_lock_nested+0x283/0x430
[<ffffffff814f06b2>] _regmap_raw_write+0x862/0x880
[<ffffffff814ec90f>] ? regmap_lock_mutex+0x2f/0x40
[<ffffffff814f0744>] _regmap_bus_raw_write+0x74/0xa0
[<ffffffff814ef3d2>] _regmap_write+0x92/0x140
[<ffffffff814f0b7b>] regmap_write+0x4b/0x70
[<ffffffffa032b090>] ? dvb_frontend_release+0x110/0x110 [dvb_core]
[<ffffffffa05141d4>] e4000_init+0x34/0x210 [e4000]
[<ffffffffa032a029>] dvb_frontend_init+0x59/0xc0 [dvb_core]
[<ffffffff810bde30>] ? finish_task_switch+0x80/0x180
[<ffffffff810bddf2>] ? finish_task_switch+0x42/0x180
[<ffffffffa032b116>] dvb_frontend_thread+0x86/0x7b0 [dvb_core]
[<ffffffff817a9203>] ? __schedule+0x343/0x930
[<ffffffffa032b090>] ? dvb_frontend_release+0x110/0x110 [dvb_core]
[<ffffffff810b826b>] kthread+0x10b/0x130
[<ffffffff81020099>] ? sched_clock+0x9/0x10
[<ffffffff810b8160>] ? kthread_create_on_node+0x250/0x250
[<ffffffff817b063c>] ret_from_fork+0x7c/0xb0
[<ffffffff810b8160>] ? kthread_create_on_node+0x250/0x250

Signed-off-by: Antti Palosaari <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/dvb-frontends/rtl2832.c

···
 	return 0;
 }
 
+/*
+ * FIXME: Hack. Implement own regmap locking in order to silence lockdep
+ * recursive lock warning. That happens when regmap I2C client calls I2C mux
+ * adapter, which leads demod I2C repeater enable via demod regmap. Operation
+ * takes two regmap locks recursively - but those are different regmap instances
+ * in a two different I2C drivers, so it is not deadlock. Proper fix is to make
+ * regmap aware of lockdep.
+ */
+static void rtl2832_regmap_lock(void *__dev)
+{
+	struct rtl2832_dev *dev = __dev;
+	struct i2c_client *client = dev->client;
+
+	dev_dbg(&client->dev, "\n");
+	mutex_lock(&dev->regmap_mutex);
+}
+
+static void rtl2832_regmap_unlock(void *__dev)
+{
+	struct rtl2832_dev *dev = __dev;
+	struct i2c_client *client = dev->client;
+
+	dev_dbg(&client->dev, "\n");
+	mutex_unlock(&dev->regmap_mutex);
+}
+
 static struct dvb_frontend *rtl2832_get_dvb_frontend(struct i2c_client *client)
 {
 	struct rtl2832_dev *dev = i2c_get_clientdata(client);
···
 			.range_max        = 5 * 0x100,
 		},
 	};
-	static const struct regmap_config regmap_config = {
-		.reg_bits    =  8,
-		.val_bits    =  8,
-		.volatile_reg = rtl2832_volatile_reg,
-		.max_register = 5 * 0x100,
-		.ranges = regmap_range_cfg,
-		.num_ranges = ARRAY_SIZE(regmap_range_cfg),
-		.cache_type = REGCACHE_RBTREE,
-	};
 
 	dev_dbg(&client->dev, "\n");
 
···
 	INIT_DELAYED_WORK(&dev->i2c_gate_work, rtl2832_i2c_gate_work);
 	INIT_DELAYED_WORK(&dev->stat_work, rtl2832_stat_work);
 	/* create regmap */
+	mutex_init(&dev->regmap_mutex);
+	dev->regmap_config.reg_bits =  8,
+	dev->regmap_config.val_bits =  8,
+	dev->regmap_config.lock = rtl2832_regmap_lock,
+	dev->regmap_config.unlock = rtl2832_regmap_unlock,
+	dev->regmap_config.lock_arg = dev,
+	dev->regmap_config.volatile_reg = rtl2832_volatile_reg,
+	dev->regmap_config.max_register = 5 * 0x100,
+	dev->regmap_config.ranges = regmap_range_cfg,
+	dev->regmap_config.num_ranges = ARRAY_SIZE(regmap_range_cfg),
+	dev->regmap_config.cache_type = REGCACHE_RBTREE,
 	dev->regmap = regmap_init(&client->dev, &regmap_bus, client,
-				  &regmap_config);
+				  &dev->regmap_config);
 	if (IS_ERR(dev->regmap)) {
 		ret = PTR_ERR(dev->regmap);
 		goto err_kfree;

drivers/media/dvb-frontends/rtl2832_priv.h

···
 struct rtl2832_dev {
 	struct rtl2832_platform_data *pdata;
 	struct i2c_client *client;
+	struct mutex regmap_mutex;
+	struct regmap_config regmap_config;
 	struct regmap *regmap;
 	struct i2c_adapter *i2c_adapter_tuner;
 	struct dvb_frontend fe;