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Message-ID: <8230613.T7Z3S40VBb@steina-w>
Date: Wed, 31 May 2023 09:37:50 +0200
From: Alexander Stein <alexander.stein@...tq-group.com>
To: NXP Linux Team <linux-imx@....com>,
"A. Sverdlin" <alexander.sverdlin@...mens.com>
Cc: Alexander Sverdlin <alexander.sverdlin@...mens.com>,
Dong Aisheng <aisheng.dong@....com>,
Shawn Guo <shawnguo@...nel.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
Fabio Estevam <festevam@...il.com>, linux-i2c@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] i2c: lpi2c: cache peripheral clock rate
Hi,
Am Montag, 15. Mai 2023, 22:18:44 CEST schrieb A. Sverdlin:
> From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
>
> 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):
Looks good to me. Thanks.
Reviewed-by: Alexander Stein <alexander.stein@...tq-group.com>
> ======================================================
> 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@...mens.com>
> ---
> Changelog:
> v4: switched to atomic_t
> included clk_rate_exclusive_get()/clk_rate_exclusive_put()
> v3: fixed build error reported by kernel test robot <lkp@...el.com>
>
> https://lore.kernel.org/oe-kbuild-all/202303102010.pAv56wKs-lkp@intel.com/
> v2: added clk_notifier as Alexander suggested
>
> drivers/i2c/busses/i2c-imx-lpi2c.c | 47 +++++++++++++++++++++++++++---
> 1 file changed, 43 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> b/drivers/i2c/busses/i2c-imx-lpi2c.c index 1af0a637d7f1..b31d29d684fa
> 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>
> @@ -100,6 +101,8 @@ 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;
> @@ -198,25 +201,39 @@ 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)
> {
> 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)
> - - 3 - (filt >> 1);
> + clk_cycle = atomic_read(&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;
> if (clklo < 64)
> @@ -594,6 +611,28 @@ 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);
--
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