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Subject[PATCH 5.2 093/137] i2c-cht-wc: Fix lockdep warning
Date
From: Hans de Goede <hdegoede@redhat.com>

[ Upstream commit 232219b9a464c2479c98aa589acb1bd3383ae9d6 ]

When the kernel is build with lockdep support and the i2c-cht-wc driver is
used, the following warning is shown:

[ 66.674334] ======================================================
[ 66.674337] WARNING: possible circular locking dependency detected
[ 66.674340] 5.3.0-rc4+ #83 Not tainted
[ 66.674342] ------------------------------------------------------
[ 66.674345] systemd-udevd/1232 is trying to acquire lock:
[ 66.674349] 00000000a74dab07 (intel_soc_pmic_chtwc:167:(&cht_wc_regmap_cfg)->lock){+.+.}, at: regmap_write+0x31/0x70
[ 66.674360]
but task is already holding lock:
[ 66.674362] 00000000d44a85b7 (i2c_register_adapter){+.+.}, at: i2c_smbus_xfer+0x49/0xf0
[ 66.674370]
which lock already depends on the new lock.

[ 66.674371]
the existing dependency chain (in reverse order) is:
[ 66.674374]
-> #1 (i2c_register_adapter){+.+.}:
[ 66.674381] rt_mutex_lock_nested+0x46/0x60
[ 66.674384] i2c_smbus_xfer+0x49/0xf0
[ 66.674387] i2c_smbus_read_byte_data+0x45/0x70
[ 66.674391] cht_wc_byte_reg_read+0x35/0x50
[ 66.674394] _regmap_read+0x63/0x1a0
[ 66.674396] _regmap_update_bits+0xa8/0xe0
[ 66.674399] regmap_update_bits_base+0x63/0xa0
[ 66.674403] regmap_irq_update_bits.isra.0+0x3b/0x50
[ 66.674406] regmap_add_irq_chip+0x592/0x7a0
[ 66.674409] devm_regmap_add_irq_chip+0x89/0xed
[ 66.674412] cht_wc_probe+0x102/0x158
[ 66.674415] i2c_device_probe+0x95/0x250
[ 66.674419] really_probe+0xf3/0x380
[ 66.674422] driver_probe_device+0x59/0xd0
[ 66.674425] device_driver_attach+0x53/0x60
[ 66.674428] __driver_attach+0x92/0x150
[ 66.674431] bus_for_each_dev+0x7d/0xc0
[ 66.674434] bus_add_driver+0x14d/0x1f0
[ 66.674437] driver_register+0x6d/0xb0
[ 66.674440] i2c_register_driver+0x45/0x80
[ 66.674445] do_one_initcall+0x60/0x2f4
[ 66.674450] kernel_init_freeable+0x20d/0x2b4
[ 66.674453] kernel_init+0xa/0x10c
[ 66.674457] ret_from_fork+0x3a/0x50
[ 66.674459]
-> #0 (intel_soc_pmic_chtwc:167:(&cht_wc_regmap_cfg)->lock){+.+.}:
[ 66.674465] __lock_acquire+0xe07/0x1930
[ 66.674468] lock_acquire+0x9d/0x1a0
[ 66.674472] __mutex_lock+0xa8/0x9a0
[ 66.674474] regmap_write+0x31/0x70
[ 66.674480] cht_wc_i2c_adap_smbus_xfer+0x72/0x240 [i2c_cht_wc]
[ 66.674483] __i2c_smbus_xfer+0x1a3/0x640
[ 66.674486] i2c_smbus_xfer+0x67/0xf0
[ 66.674489] i2c_smbus_read_byte_data+0x45/0x70
[ 66.674494] bq24190_probe+0x26b/0x410 [bq24190_charger]
[ 66.674497] i2c_device_probe+0x189/0x250
[ 66.674500] really_probe+0xf3/0x380
[ 66.674503] driver_probe_device+0x59/0xd0
[ 66.674506] device_driver_attach+0x53/0x60
[ 66.674509] __driver_attach+0x92/0x150
[ 66.674512] bus_for_each_dev+0x7d/0xc0
[ 66.674515] bus_add_driver+0x14d/0x1f0
[ 66.674518] driver_register+0x6d/0xb0
[ 66.674521] i2c_register_driver+0x45/0x80
[ 66.674524] do_one_initcall+0x60/0x2f4
[ 66.674528] do_init_module+0x5c/0x230
[ 66.674531] load_module+0x2707/0x2a20
[ 66.674534] __do_sys_init_module+0x188/0x1b0
[ 66.674537] do_syscall_64+0x5c/0xb0
[ 66.674541] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 66.674543]
other info that might help us debug this:

[ 66.674545] Possible unsafe locking scenario:

[ 66.674547] CPU0 CPU1
[ 66.674548] ---- ----
[ 66.674550] lock(i2c_register_adapter);
[ 66.674553] lock(intel_soc_pmic_chtwc:167:(&cht_wc_regmap_cfg)->lock);
[ 66.674556] lock(i2c_register_adapter);
[ 66.674559] lock(intel_soc_pmic_chtwc:167:(&cht_wc_regmap_cfg)->lock);
[ 66.674561]
*** DEADLOCK ***

The problem is that the CHT Whiskey Cove PMIC's builtin i2c-adapter is
itself a part of an i2c-client (the PMIC). This means that transfers done
through it take adapter->bus_lock twice, once for the parent i2c-adapter
and once for its own bus_lock. Lockdep does not like this nested locking.

To make lockdep happy in the case of busses with muxes, the i2c-core's
i2c_adapter_lock_bus function calls:

rt_mutex_lock_nested(&adapter->bus_lock, i2c_adapter_depth(adapter));

But i2c_adapter_depth only works when the direct parent of the adapter is
another adapter, as it is only meant for muxes. In this case there is an
i2c-client and MFD instantiated platform_device in the parent->child chain
between the 2 devices.

This commit overrides the default i2c_lock_operations, passing a hardcoded
depth of 1 to rt_mutex_lock_nested, making lockdep happy.

Note that if there were to be a mux attached to the i2c-wc-cht adapter,
this would break things again since the i2c-mux code expects the
root-adapter to have a locking depth of 0. But the i2c-wc-cht adapter
always has only 1 client directly attached in the form of the charger IC
paired with the CHT Whiskey Cove PMIC.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/i2c/busses/i2c-cht-wc.c | 46 +++++++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)

diff --git a/drivers/i2c/busses/i2c-cht-wc.c b/drivers/i2c/busses/i2c-cht-wc.c
index 66af44bfa67d5..f6546de66fbc8 100644
--- a/drivers/i2c/busses/i2c-cht-wc.c
+++ b/drivers/i2c/busses/i2c-cht-wc.c
@@ -178,6 +178,51 @@ static const struct i2c_algorithm cht_wc_i2c_adap_algo = {
.smbus_xfer = cht_wc_i2c_adap_smbus_xfer,
};

+/*
+ * We are an i2c-adapter which itself is part of an i2c-client. This means that
+ * transfers done through us take adapter->bus_lock twice, once for our parent
+ * i2c-adapter and once to take our own bus_lock. Lockdep does not like this
+ * nested locking, to make lockdep happy in the case of busses with muxes, the
+ * i2c-core's i2c_adapter_lock_bus function calls:
+ * rt_mutex_lock_nested(&adapter->bus_lock, i2c_adapter_depth(adapter));
+ *
+ * But i2c_adapter_depth only works when the direct parent of the adapter is
+ * another adapter, as it is only meant for muxes. In our case there is an
+ * i2c-client and MFD instantiated platform_device in the parent->child chain
+ * between the 2 devices.
+ *
+ * So we override the default i2c_lock_operations and pass a hardcoded
+ * depth of 1 to rt_mutex_lock_nested, to make lockdep happy.
+ *
+ * Note that if there were to be a mux attached to our adapter, this would
+ * break things again since the i2c-mux code expects the root-adapter to have
+ * a locking depth of 0. But we always have only 1 client directly attached
+ * in the form of the Charger IC paired with the CHT Whiskey Cove PMIC.
+ */
+static void cht_wc_i2c_adap_lock_bus(struct i2c_adapter *adapter,
+ unsigned int flags)
+{
+ rt_mutex_lock_nested(&adapter->bus_lock, 1);
+}
+
+static int cht_wc_i2c_adap_trylock_bus(struct i2c_adapter *adapter,
+ unsigned int flags)
+{
+ return rt_mutex_trylock(&adapter->bus_lock);
+}
+
+static void cht_wc_i2c_adap_unlock_bus(struct i2c_adapter *adapter,
+ unsigned int flags)
+{
+ rt_mutex_unlock(&adapter->bus_lock);
+}
+
+static const struct i2c_lock_operations cht_wc_i2c_adap_lock_ops = {
+ .lock_bus = cht_wc_i2c_adap_lock_bus,
+ .trylock_bus = cht_wc_i2c_adap_trylock_bus,
+ .unlock_bus = cht_wc_i2c_adap_unlock_bus,
+};
+
/**** irqchip for the client connected to the extchgr i2c adapter ****/
static void cht_wc_i2c_irq_lock(struct irq_data *data)
{
@@ -286,6 +331,7 @@ static int cht_wc_i2c_adap_i2c_probe(struct platform_device *pdev)
adap->adapter.owner = THIS_MODULE;
adap->adapter.class = I2C_CLASS_HWMON;
adap->adapter.algo = &cht_wc_i2c_adap_algo;
+ adap->adapter.lock_ops = &cht_wc_i2c_adap_lock_ops;
strlcpy(adap->adapter.name, "PMIC I2C Adapter",
sizeof(adap->adapter.name));
adap->adapter.dev.parent = &pdev->dev;
--
2.20.1


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