Re: [PATCH v3] i2c: lpi2c: cache peripheral clock rate

[Alexander Stein]

Am Freitag, 10. März 2023, 14:08:15 CEST schrieb A. Sverdlin:
> 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>

Reviewed-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>

Note: [1] needs to be applied as well in order to get rid of all the lockdep 
errors.

[1] https://lore.kernel.org/linux-i2c/20230424080627.20564-1-alexander.stein@xxxxxxxxxxxxxxx/T/#u

> ---
>  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@xxxxxxxxx>
>    
> https://lore.kernel.org/oe-kbuild-all/202303102010.pAv56wKs-lkp@xxxxxxxxx/
> 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);


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