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
------------------------------------------------------
fs-value/2332 is trying to acquire lock:
ffff8000096cae08 (prepare_lock){+.+.}-{3:3}, at: clk_prepare_lock
but task is already holding lock:
ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at: i2c_adapter_lock_bus
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (i2c_register_adapter){+.+.}-{3:3}:
lock_acquire
rt_mutex_lock_nested
i2c_adapter_lock_bus
i2c_transfer
regmap_i2c_read
_regmap_raw_read
_regmap_bus_read
_regmap_read
regmap_read
pcf85063_probe
i2c_device_probe
really_probe
__driver_probe_device
driver_probe_device
__device_attach_driver
bus_for_each_drv
__device_attach
device_initial_probe
bus_probe_device
device_add
device_register
i2c_new_client_device
of_i2c_register_devices
i2c_register_adapter
__i2c_add_numbered_adapter
i2c_add_adapter
lpi2c_imx_probe
platform_probe
really_probe
__driver_probe_device
driver_probe_device
__device_attach_driver
bus_for_each_drv
__device_attach
device_initial_probe
bus_probe_device
deferred_probe_work_func
process_one_work
worker_thread
kthread
ret_from_fork
-> #1 (rtc_pcf85063:560:(&config->regmap)->lock){+.+.}-{3:3}:
lock_acquire
__mutex_lock
mutex_lock_nested
regmap_lock_mutex
regmap_read
pcf85063_clkout_recalc_rate
__clk_register
devm_clk_register
pcf85063_probe
i2c_device_probe
really_probe
__driver_probe_device
driver_probe_device
__device_attach_driver
bus_for_each_drv
__device_attach
device_initial_probe
bus_probe_device
device_add
device_register
i2c_new_client_device
of_i2c_register_devices
i2c_register_adapter
__i2c_add_numbered_adapter
i2c_add_adapter
lpi2c_imx_probe
platform_probe
really_probe
__driver_probe_device
driver_probe_device
__device_attach_driver
bus_for_each_drv
__device_attach
device_initial_probe
bus_probe_device
deferred_probe_work_func
process_one_work
worker_thread
kthread
ret_from_fork
-> #0 (prepare_lock){+.+.}-{3:3}:
__lock_acquire
lock_acquire.part.0
lock_acquire
__mutex_lock
mutex_lock_nested
clk_prepare_lock
clk_get_rate
lpi2c_imx_xfer
__i2c_transfer
i2c_transfer
regmap_i2c_read
_regmap_raw_read
regmap_raw_read
regmap_bulk_read
at24_read
nvmem_reg_read
bin_attr_nvmem_read
sysfs_kf_bin_read
kernfs_fop_read_iter
new_sync_read
vfs_read
ksys_read
__arm64_sys_read
invoke_syscall
...
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
#1: ffff000010fe4400 (kn->active#72){.+.+}-{0:0}, at: kernfs_fop_read_iter
#2: ffff0000110168e8 (&at24->lock){+.+.}-{3:3}, at: at24_read
#3: ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at: i2c_adapter_lock_bus
stack backtrace:
CPU: 1 PID: 2332 Comm: ... Tainted: G O 5.15.71+... #1
Hardware name: ... (DT)
Call trace:
dump_backtrace
show_stack
dump_stack_lvl
dump_stack
print_circular_bug
check_noncircular
__lock_acquire
lock_acquire.part.0
lock_acquire
__mutex_lock
mutex_lock_nested
clk_prepare_lock
clk_get_rate
lpi2c_imx_xfer
__i2c_transfer
i2c_transfer
regmap_i2c_read
_regmap_raw_read
regmap_raw_read
regmap_bulk_read
at24_read
nvmem_reg_read
bin_attr_nvmem_read
sysfs_kf_bin_read
kernfs_fop_read_iter
new_sync_read
vfs_read
ksys_read
__arm64_sys_read
invoke_syscall
...
Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
---
drivers/i2c/busses/i2c-imx-lpi2c.c | 33 +++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)
Changelog:
v2: added clk_notifier as Alexander suggested
diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
index 188f2a36d2fd6..5f1d1d4e018bd 100644
--- a/drivers/i2c/busses/i2c-imx-lpi2c.c
+++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
@@ -100,6 +100,8 @@ struct lpi2c_imx_struct {
__u8 *rx_buf;
__u8 *tx_buf;
struct completion complete;
+ struct notifier_block clk_change_nb;
+ unsigned int rate_per;
unsigned int msglen;
unsigned int delivered;
unsigned int block_data;
@@ -198,24 +200,37 @@ 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(&ndata->clk,
+ struct lpi2c_imx_struct,
+ clk_per);
+
+ if (action & POST_RATE_CHANGE)
+ 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)
{
u8 prescale, filt, sethold, clkhi, clklo, datavd;
- unsigned int clk_rate, clk_cycle;
+ unsigned int clk_cycle;
enum lpi2c_imx_pincfg pincfg;
unsigned int temp;
lpi2c_imx_set_mode(lpi2c_imx);
- clk_rate = clk_get_rate(lpi2c_imx->clks[0].clk);
if (lpi2c_imx->mode == HS || lpi2c_imx->mode == ULTRA_FAST)
filt = 0;
else
filt = 2;
for (prescale = 0; prescale <= 7; prescale++) {
- clk_cycle = clk_rate / ((1 << prescale) * lpi2c_imx->bitrate)
+ clk_cycle = lpi2c_imx->rate_per / ((1 << prescale) * lpi2c_imx->bitrate)
- 3 - (filt >> 1);
clkhi = (clk_cycle + I2C_CLK_RATIO) / (I2C_CLK_RATIO + 1);
clklo = clk_cycle - clkhi;
@@ -588,6 +603,18 @@ 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");
+ lpi2c_imx->rate_per = clk_get_rate(lpi2c_imx->clks[0].clk);
+ if (!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
