[PATCH] i2c: lpi2c: cache peripheral clock rate

From: A. Sverdlin
Date: Thu Mar 09 2023 - 08:43:32 EST

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+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>
---
drivers/i2c/busses/i2c-imx-lpi2c.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
index 188f2a36d2fd6..cf36f12b85573 100644
--- a/drivers/i2c/busses/i2c-imx-lpi2c.c
+++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
@@ -100,6 +100,7 @@ struct lpi2c_imx_struct {
__u8 *rx_buf;
__u8 *tx_buf;
struct completion complete;
+ unsigned int rate_per;
unsigned int msglen;
unsigned int delivered;
unsigned int block_data;
@@ -202,20 +203,19 @@ static void lpi2c_imx_stop(struct lpi2c_imx_struct *lpi2c_imx)
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 +588,12 @@ static int lpi2c_imx_probe(struct platform_device *pdev)
if (ret)
return ret;

+ 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