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    Subject[PATCH v3] i2c: lpi2c: cache peripheral clock rate
    Date
    From: Alexander Sverdlin <alexander.sverdlin@siemens.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):

    ======================================================
    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@siemens.com>
    ---
    drivers/i2c/busses/i2c-imx-lpi2c.c | 33 +++++++++++++++++++++++++++---
    1 file changed, 30 insertions(+), 3 deletions(-)

    Changelog:
    v3: fixed build error reported by kernel test robot <lkp@intel.com>
    https://lore.kernel.org/oe-kbuild-all/202303102010.pAv56wKs-lkp@intel.com/
    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(nb,
    + struct lpi2c_imx_struct,
    + clk_change_nb);
    +
    + 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
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