From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
One of the reasons to do it is to save some CPU cycles on cpu_freq_get()
under mutex. The second reason if the (false-positive) lockdep splat caused
by the recursive feature of the "prepare_lock" (one clock instance is I2C
peripheral clock and another is pcf85063 RTC as clock provider):
======================================================
WARNING: possible circular locking dependency detected
5.15.71+... #1 Tainted: G O
------------------------------------------------------
.../2332 is trying to acquire lock:
ffff8000096cae08 (prepare_lock){+.+.}-{3:3}, at: clk_prepare_lock+0x50/0xb0
but task is already holding lock:
ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at: i2c_adapter_lock_bus+0x2c/0x3c
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (i2c_register_adapter){+.+.}-{3:3}:
lock_acquire+0x68/0x8c
rt_mutex_lock_nested+0x88/0xe0
i2c_adapter_lock_bus+0x2c/0x3c
i2c_transfer+0x58/0x130
regmap_i2c_read+0x64/0xb0
_regmap_raw_read+0x114/0x440
_regmap_bus_read+0x4c/0x84
_regmap_read+0x6c/0x270
regmap_read+0x54/0x80
pcf85063_probe+0xec/0x4cc
i2c_device_probe+0x10c/0x350
really_probe+0xc4/0x470
__driver_probe_device+0x11c/0x190
driver_probe_device+0x48/0x110
__device_attach_driver+0xc4/0x160
bus_for_each_drv+0x80/0xe0
__device_attach+0xb0/0x1f0
device_initial_probe+0x1c/0x2c
bus_probe_device+0xa4/0xb0
device_add+0x398/0x8ac
device_register+0x28/0x40
i2c_new_client_device+0x144/0x290
of_i2c_register_devices+0x18c/0x230
i2c_register_adapter+0x1dc/0x6b0
__i2c_add_numbered_adapter+0x68/0xbc
i2c_add_adapter+0xb0/0xe0
lpi2c_imx_probe+0x354/0x5e0
platform_probe+0x70/0xec
really_probe+0xc4/0x470
__driver_probe_device+0x11c/0x190
driver_probe_device+0x48/0x110
__device_attach_driver+0xc4/0x160
bus_for_each_drv+0x80/0xe0
__device_attach+0xb0/0x1f0
device_initial_probe+0x1c/0x2c
bus_probe_device+0xa4/0xb0
deferred_probe_work_func+0xa0/0xfc
process_one_work+0x2ac/0x6f4
worker_thread+0x7c/0x47c
kthread+0x150/0x16c
ret_from_fork+0x10/0x20
-> #1 (rtc_pcf85063:560:(&config->regmap)->lock){+.+.}-{3:3}:
lock_acquire+0x68/0x8c
__mutex_lock+0x9c/0x4d0
mutex_lock_nested+0x48/0x5c
regmap_lock_mutex+0x1c/0x30
regmap_read+0x44/0x80
pcf85063_clkout_recalc_rate+0x34/0x80
__clk_register+0x520/0x880
devm_clk_register+0x64/0xc4
pcf85063_probe+0x24c/0x4cc
i2c_device_probe+0x10c/0x350
really_probe+0xc4/0x470
__driver_probe_device+0x11c/0x190
driver_probe_device+0x48/0x110
__device_attach_driver+0xc4/0x160
bus_for_each_drv+0x80/0xe0
__device_attach+0xb0/0x1f0
device_initial_probe+0x1c/0x2c
bus_probe_device+0xa4/0xb0
device_add+0x398/0x8ac
device_register+0x28/0x40
i2c_new_client_device+0x144/0x290
of_i2c_register_devices+0x18c/0x230
i2c_register_adapter+0x1dc/0x6b0
__i2c_add_numbered_adapter+0x68/0xbc
i2c_add_adapter+0xb0/0xe0
lpi2c_imx_probe+0x354/0x5e0
platform_probe+0x70/0xec
really_probe+0xc4/0x470
__driver_probe_device+0x11c/0x190
driver_probe_device+0x48/0x110
__device_attach_driver+0xc4/0x160
bus_for_each_drv+0x80/0xe0
__device_attach+0xb0/0x1f0
device_initial_probe+0x1c/0x2c
bus_probe_device+0xa4/0xb0
deferred_probe_work_func+0xa0/0xfc
process_one_work+0x2ac/0x6f4
worker_thread+0x7c/0x47c
kthread+0x150/0x16c
ret_from_fork+0x10/0x20
-> #0 (prepare_lock){+.+.}-{3:3}:
__lock_acquire+0x1298/0x20d0
lock_acquire.part.0+0xf0/0x250
lock_acquire+0x68/0x8c
__mutex_lock+0x9c/0x4d0
mutex_lock_nested+0x48/0x5c
clk_prepare_lock+0x50/0xb0
clk_get_rate+0x28/0x80
lpi2c_imx_xfer+0xb0/0xa9c
__i2c_transfer+0x174/0xa80
i2c_transfer+0x68/0x130
regmap_i2c_read+0x64/0xb0
_regmap_raw_read+0x114/0x440
regmap_raw_read+0x19c/0x28c
regmap_bulk_read+0x1b8/0x244
at24_read+0x14c/0x2c4
nvmem_reg_read+0x2c/0x54
bin_attr_nvmem_read+0x8c/0xbc
sysfs_kf_bin_read+0x74/0x94
kernfs_fop_read_iter+0xb0/0x1d0
new_sync_read+0xf0/0x184
vfs_read+0x154/0x1f0
ksys_read+0x70/0x100
__arm64_sys_read+0x24/0x30
invoke_syscall+0x50/0x120
el0_svc_common.constprop.0+0x68/0x124
do_el0_svc+0x30/0x9c
el0_svc+0x54/0x110
el0t_64_sync_handler+0xa4/0x130
el0t_64_sync+0x1a0/0x1a4
other info that might help us debug this:
Chain exists of:
prepare_lock --> rtc_pcf85063:560:(&config->regmap)->lock --> i2c_register_adapter
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(i2c_register_adapter);
lock(rtc_pcf85063:560:(&config->regmap)->lock);
lock(i2c_register_adapter);
lock(prepare_lock);
*** DEADLOCK ***
4 locks held by .../2332:
#0: ffff0000146eb288 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_read_iter+0x74/0x1d0
#1: ffff000010fe4400 (kn->active#72){.+.+}-{0:0}, at: kernfs_fop_read_iter+0x7c/0x1d0
#2: ffff0000110168e8 (&at24->lock){+.+.}-{3:3}, at: at24_read+0x8c/0x2c4
#3: ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at: i2c_adapter_lock_bus+0x2c/0x3c
stack backtrace:
CPU: 1 PID: 2332 Comm: ... Tainted: G O 5.15.71+... #1
Hardware name: ... (DT)
Call trace:
dump_backtrace+0x0/0x1d4
show_stack+0x20/0x2c
dump_stack_lvl+0x8c/0xb8
dump_stack+0x18/0x34
print_circular_bug+0x1f8/0x200
check_noncircular+0x130/0x144
__lock_acquire+0x1298/0x20d0
lock_acquire.part.0+0xf0/0x250
lock_acquire+0x68/0x8c
__mutex_lock+0x9c/0x4d0
mutex_lock_nested+0x48/0x5c
clk_prepare_lock+0x50/0xb0
clk_get_rate+0x28/0x80
lpi2c_imx_xfer+0xb0/0xa9c
__i2c_transfer+0x174/0xa80
i2c_transfer+0x68/0x130
regmap_i2c_read+0x64/0xb0
_regmap_raw_read+0x114/0x440
regmap_raw_read+0x19c/0x28c
regmap_bulk_read+0x1b8/0x244
at24_read+0x14c/0x2c4
nvmem_reg_read+0x2c/0x54
bin_attr_nvmem_read+0x8c/0xbc
sysfs_kf_bin_read+0x74/0x94
kernfs_fop_read_iter+0xb0/0x1d0
new_sync_read+0xf0/0x184
vfs_read+0x154/0x1f0
ksys_read+0x70/0x100
__arm64_sys_read+0x24/0x30
invoke_syscall+0x50/0x120
el0_svc_common.constprop.0+0x68/0x124
do_el0_svc+0x30/0x9c
el0_svc+0x54/0x110
el0t_64_sync_handler+0xa4/0x130
el0t_64_sync+0x1a0/0x1a4
Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
Reviewed-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>
Signed-off-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>
---
This is a v6 picking up Alexander Sverdlin's patch. Up to v5 is done by
Alexander Sverdlin.
I'm not sure if in this case both my R-b and S-o-b are necessary/desired.
Changelog:
v6: - rebased to next-20231017
- Just replaced clk_get_rate with atomic_read to shrink the diff
v5: rebased onto Wolfram's i2c/for-next
v4: switched to atomic_t
included clk_rate_exclusive_get()/clk_rate_exclusive_put()
v3: fixed build error reported by kernel test robot <lkp@xxxxxxxxx>
https://lore.kernel.org/oe-kbuild-all/202303102010.pAv56wKs-lkp@xxxxxxxxx/
v2: added clk_notifier as Alexander suggested
drivers/i2c/busses/i2c-imx-lpi2c.c | 41 +++++++++++++++++++++++++++++-
1 file changed, 40 insertions(+), 1 deletion(-)
diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
index 678b30e90492a..e04faa261e7b1 100644
--- a/drivers/i2c/busses/i2c-imx-lpi2c.c
+++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
@@ -5,6 +5,7 @@
* Copyright 2016 Freescale Semiconductor, Inc.
*/
+#include <linux/atomic.h>
#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/delay.h>
@@ -99,6 +100,8 @@ struct lpi2c_imx_struct {
__u8 *rx_buf;
__u8 *tx_buf;
struct completion complete;
+ struct notifier_block clk_change_nb;
+ atomic_t rate_per;
unsigned int msglen;
unsigned int delivered;
unsigned int block_data;
@@ -197,6 +200,20 @@ static void lpi2c_imx_stop(struct lpi2c_imx_struct *lpi2c_imx)
} while (1);
}
+static int lpi2c_imx_clk_change_cb(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct clk_notifier_data *ndata = data;
+ struct lpi2c_imx_struct *lpi2c_imx = container_of(nb,
+ struct lpi2c_imx_struct,
+ clk_change_nb);
+
+ if (action & POST_RATE_CHANGE)
+ atomic_set(&lpi2c_imx->rate_per, ndata->new_rate);
+
+ return NOTIFY_OK;
+}
+
/* CLKLO = I2C_CLK_RATIO * CLKHI, SETHOLD = CLKHI, DATAVD = CLKHI/2 */
static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
{
@@ -207,7 +224,7 @@ static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
lpi2c_imx_set_mode(lpi2c_imx);
- clk_rate = clk_get_rate(lpi2c_imx->clks[0].clk);
+ clk_rate = atomic_read(&lpi2c_imx->rate_per);
if (!clk_rate)
return -EINVAL;
@@ -590,6 +607,28 @@ static int lpi2c_imx_probe(struct platform_device *pdev)
if (ret)
return ret;
+ lpi2c_imx->clk_change_nb.notifier_call = lpi2c_imx_clk_change_cb;
+ ret = devm_clk_notifier_register(&pdev->dev, lpi2c_imx->clks[0].clk,
+ &lpi2c_imx->clk_change_nb);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "can't register peripheral clock notifier\n");
+ /*
+ * Lock the clock rate to avoid rate change between clk_get_rate() and
+ * atomic_set()
+ */
+ ret = clk_rate_exclusive_get(lpi2c_imx->clks[0].clk);
+ if (ret) {
+ dev_err(&pdev->dev, "can't lock I2C peripheral clock rate\n");
+ return ret;
+ }
+ atomic_set(&lpi2c_imx->rate_per, clk_get_rate(lpi2c_imx->clks[0].clk));
+ clk_rate_exclusive_put(lpi2c_imx->clks[0].clk);
+ if (!atomic_read(&lpi2c_imx->rate_per)) {
+ dev_err(&pdev->dev, "can't get I2C peripheral clock rate\n");
+ return -EINVAL;
+ }
+
pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
pm_runtime_use_autosuspend(&pdev->dev);
pm_runtime_get_noresume(&pdev->dev);
--
2.34.1
