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Mon, 09 Nov 2026 22:14:49 -0800 (PST) Received: from archl-rock5b ([45.112.0.182]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-375218c863csm3802316eec.28.2026.11.09.22.14.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Nov 2026 22:14:48 -0800 (PST) From: Anand Moon To: Troy Mitchell , Andi Shyti , Sebastian Reichel , Yixun Lan , Aurelien Jarno , linux-i2c@vger.kernel.org (open list:I2C SUBSYSTEM HOST DRIVERS), linux-kernel@vger.kernel.org (open list), linux-pm@vger.kernel.org (open list:SYSTEM RESET/SHUTDOWN DRIVERS), linux-riscv@lists.infradead.org (open list:RISC-V SPACEMIT SoC Support), spacemit@lists.linux.dev (open list:RISC-V SPACEMIT SoC Support) Cc: Anand Moon Subject: [PATCH v1 2/2] power: reset: spacemit-p1: Use atomic I2C transfers for power-off and restart Date: Tue, 10 Nov 2026 11:44:27 +0530 Message-ID: <20261110061429.2036-2-linux.amoon@gmail.com> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261110061429.2036-1-linux.amoon@gmail.com> References: <20261110061429.2036-1-linux.amoon@gmail.com> X-Mailing-List: linux-i2c@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The SpacemiT P1 power-off and restart handlers use regmap_set_bits() to access the PMIC. However, these handlers run in an atomic notifier context (specifically within an rcu_read_lock() critical section), while the I2C-backed regmap uses a sleepable mutex. This triggers a "WARNING: suspicious RCU usage" warning due to an illegal context switch in the RCU read-side critical section during shutdown on the Banana Pi BPI-F3: [ 563.803475] WARNING: suspicious RCU usage [ 563.807813] 7.3.1-ARCH-RISC-V #1 Not tainted [ 563.816614] ./include/linux/rcupdate.h:387 Illegal context switch in RCU read-side critical section! ... [ 563.841445] locks held by shutdown/1: 2, last CPU#0: [ 563.846694] #0: ffffffff8404fb20 (system_transition_mutex){+.+.}-{4:4}, at: __do_sys_reboot+0x230/0x29e [ 563.856806] #1: ffffffff84167860 (rcu_read_lock){....}-{1:3}, at: atomic_notifier_call_chain+0x4a/0x1c2 Replace the regmap operations with atomic I2C transfers to avoid sleeping in an atomic context. Preserve unrelated register bits through read-modify-write operations and check for atomic I2C support before registering the handlers. Obtain the I2C client from the parent device and verify that the adapter supports atomic transfers before registering the handlers. Tested on the Banana Pi BPI-F3 (SpacemiT K1). Assisted-by: LLM Cc: Troy Mitchell Cc: Aurelien Jarno Fixes: 28124cc0fb8c ("driver: reset: spacemit-p1: add driver for poweroff/reboot") Signed-off-by: Anand Moon --- drivers/power/reset/spacemit-p1-reboot.c | 86 ++++++++++++++++++++---- 1 file changed, 74 insertions(+), 12 deletions(-) diff --git a/drivers/power/reset/spacemit-p1-reboot.c b/drivers/power/reset/spacemit-p1-reboot.c index c0454b547718..8fcb3eadddf3 100644 --- a/drivers/power/reset/spacemit-p1-reboot.c +++ b/drivers/power/reset/spacemit-p1-reboot.c @@ -4,8 +4,9 @@ */ #include +#include +#include #include -#include #include /* Power Control Register 2 */ @@ -13,13 +14,68 @@ #define PWR_CTRL2_SHUTDOWN BIT(2) /* Shutdown request */ #define PWR_CTRL2_RST BIT(1) /* Reset request */ +static int spacemit_p1_read_atomic(struct i2c_client *client, + u8 reg, u8 *val) +{ + struct i2c_msg msgs[] = { + { + .addr = client->addr, + .flags = client->flags & I2C_M_TEN, + .len = 1, + .buf = ®, + }, + { + .addr = client->addr, + .flags = (client->flags & I2C_M_TEN) | I2C_M_RD, + .len = 1, + .buf = val, + }, + }; + int ret; + + ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs)); + + return ret == ARRAY_SIZE(msgs) ? 0 : ret < 0 ? ret : -EIO; +} + +static int spacemit_p1_write_atomic(struct i2c_client *client, + u8 reg, u8 val) +{ + u8 buf[] = { reg, val }; + struct i2c_msg msg = { + .addr = client->addr, + .flags = client->flags & I2C_M_TEN, + .len = sizeof(buf), + .buf = buf, + }; + int ret; + + ret = i2c_transfer(client->adapter, &msg, 1); + + return ret == 1 ? 0 : ret < 0 ? ret : -EIO; +} + +static int spacemit_p1_update_bits_atomic(struct i2c_client *client, + u8 reg, u8 mask) +{ + u8 val; + int ret; + + ret = spacemit_p1_read_atomic(client, reg, &val); + if (ret) + return ret; + + return spacemit_p1_write_atomic(client, reg, val | mask); +} + static int spacemit_p1_pwroff_handler(struct sys_off_data *data) { - struct regmap *regmap = data->cb_data; + struct i2c_client *client = data->cb_data; int ret; /* Put the PMIC into shutdown state */ - ret = regmap_set_bits(regmap, PWR_CTRL2, PWR_CTRL2_SHUTDOWN); + ret = spacemit_p1_update_bits_atomic(client, PWR_CTRL2, + PWR_CTRL2_SHUTDOWN); if (ret) { dev_err(data->dev, "shutdown failed: %d\n", ret); return notifier_from_errno(ret); @@ -30,11 +86,12 @@ static int spacemit_p1_pwroff_handler(struct sys_off_data *data) static int spacemit_p1_restart_handler(struct sys_off_data *data) { - struct regmap *regmap = data->cb_data; + struct i2c_client *client = data->cb_data; int ret; /* Put the PMIC into reset state */ - ret = regmap_set_bits(regmap, PWR_CTRL2, PWR_CTRL2_RST); + ret = spacemit_p1_update_bits_atomic(client, PWR_CTRL2, + PWR_CTRL2_RST); if (ret) { dev_err(data->dev, "restart failed: %d\n", ret); return notifier_from_errno(ret); @@ -46,21 +103,26 @@ static int spacemit_p1_restart_handler(struct sys_off_data *data) static int spacemit_p1_reboot_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; - struct regmap *regmap; + struct i2c_client *client; int ret; - regmap = dev_get_regmap(dev->parent, NULL); - if (!regmap) - return -ENODEV; + client = i2c_verify_client(dev->parent); + if (!client) + return dev_err_probe(dev, -ENODEV, + "Failed to find parent I2C client\n"); + + if (!client->adapter->algo->xfer_atomic) + return dev_err_probe(dev, -EOPNOTSUPP, + "Atomic I2C transfers not supported\n"); - ret = devm_register_power_off_handler(dev, &spacemit_p1_pwroff_handler, - regmap); + ret = devm_register_power_off_handler(dev, spacemit_p1_pwroff_handler, + client); if (ret) return dev_err_probe(dev, ret, "Failed to register power off handler\n"); ret = devm_register_restart_handler(dev, spacemit_p1_restart_handler, - regmap); + client); if (ret) return dev_err_probe(dev, ret, "Failed to register restart handler\n"); -- 2.56.0