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Sverdlin" To: NXP Linux Team Cc: Alexander Sverdlin , Alexander Stein , Dong Aisheng , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v3] i2c: lpi2c: cache peripheral clock rate Date: Fri, 10 Mar 2023 14:08:15 +0100 Message-Id: <20230310130815.562418-1-alexander.sverdlin@siemens.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Flowmailer-Platform: Siemens Feedback-ID: 519:519-456497:519-21489:flowmailer Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Alexander Sverdlin 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 --- 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 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