[PATCH v8 3/4] i2c: tegra: Add support for SW mutex register
From: Kartik Rajput <hidden>
Date: 2025-09-17 08:57:27
Also in:
linux-i2c, linux-tegra, lkml
Subsystem:
i2c subsystem, i2c subsystem host drivers, tegra i2c driver, the rest · Maintainers:
Andi Shyti, Laxman Dewangan, Linus Torvalds
Add support for SW mutex register introduced in Tegra264 to provide an option to share the interface between multiple firmwares and/or VMs. This involves following steps: - A firmware/OS writes its unique ID to the mutex REQUEST field. - Ownership is established when reading the GRANT field returns the same ID. - If GRANT shows a different non-zero ID, the firmware/OS retries until timeout. - After completing access, it releases the mutex by writing 0. However, the hardware does not ensure any protection based on the values. The driver/firmware should honor the peer who already holds the mutex. Signed-off-by: Kartik Rajput <redacted> Signed-off-by: Akhil R <akhilrajeev@nvidia.com> --- v7 -> v8: * Use `bool` instead of `int` for `locked` variable in tegra_i2c_mutex_lock() function. v6 -> v7: * Return bool from tegra_i2c_mutex_acquired() and tegra_i2c_mutex_trylock() functions. * Move `has_mutex` check inside tegra_i2c_mutex_lock/unlock functions. * Remove redundant empty line added in tegra_i2c_xfer() in v6. * Fix pm_runtime_put() not getting called if mutex unlock fails. * In tegra_i2c_mutex_lock() simplify the logic to check if the mutex is acquired or not by checking the value of `ret` variable. * Update commit message to describe the functioning of SW mutex feature. v4 -> v6: * Guard tegra_i2c_mutex_lock() and tegra_i2c_mutex_unlock() to ensure that they are called on platforms which support SW mutex. v3 -> v4: * Update timeout logic of tegra_i2c_mutex_lock() to use read_poll_timeout APIs for improving timeout logic. * Add tegra_i2c_mutex_acquired() to check if mutex is acquired or not. * Rename I2C_SW_MUTEX_ID as I2C_SW_MUTEX_ID_CCPLEX. * Function tegra_i2c_poll_register() was moved unnecessarily, it has now been moved to its original location. * Use tegra_i2c_mutex_lock/unlock APIs in the tegra_i2c_xfer() function. This ensures proper propagation of error in case mutex lock fails. Please note that as the function tegra_i2c_xfer() is already guarded by the bus lock operation there is no need of additional lock for the tegra_i2c_mutex_lock/unlock APIs. v2 -> v3: * Update tegra_i2c_mutex_trylock and tegra_i2c_mutex_unlock to use readl and writel APIs instead of i2c_readl and i2c_writel which use relaxed APIs. * Use dev_warn instead of WARN_ON if mutex lock/unlock fails. v1 -> v2: * Fixed typos. * Fix tegra_i2c_mutex_lock() logic. * Add a timeout in tegra_i2c_mutex_lock() instead of polling for mutex indefinitely. --- drivers/i2c/busses/i2c-tegra.c | 92 ++++++++++++++++++++++++++++++++++ 1 file changed, 92 insertions(+)
diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 6f816de8b3af..a2119b8bcc1d 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c@@ -137,6 +137,14 @@ #define I2C_MASTER_RESET_CNTRL 0x0a8 +#define I2C_SW_MUTEX 0x0ec +#define I2C_SW_MUTEX_REQUEST GENMASK(3, 0) +#define I2C_SW_MUTEX_GRANT GENMASK(7, 4) +#define I2C_SW_MUTEX_ID_CCPLEX 9 + +/* SW mutex acquire timeout value in microseconds. */ +#define I2C_SW_MUTEX_TIMEOUT_US (25 * USEC_PER_MSEC) + /* configuration load timeout in microseconds */ #define I2C_CONFIG_LOAD_TIMEOUT 1000000
@@ -210,6 +218,7 @@ enum msg_end_type { * @has_interface_timing_reg: Has interface timing register to program the tuned * timing settings. * @has_hs_mode_support: Has support for high speed (HS) mode transfers. + * @has_mutex: Has mutex register for mutual exclusion with other firmwares or VMs. */ struct tegra_i2c_hw_feature { bool has_continue_xfer_support;
@@ -237,6 +246,7 @@ struct tegra_i2c_hw_feature { u32 setup_hold_time_hs_mode; bool has_interface_timing_reg; bool has_hs_mode_support; + bool has_mutex; }; /**
@@ -381,6 +391,76 @@ static void i2c_readsl(struct tegra_i2c_dev *i2c_dev, void *data, readsl(i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg), data, len); } +static bool tegra_i2c_mutex_acquired(struct tegra_i2c_dev *i2c_dev) +{ + unsigned int reg = tegra_i2c_reg_addr(i2c_dev, I2C_SW_MUTEX); + u32 val, id; + + val = readl(i2c_dev->base + reg); + id = FIELD_GET(I2C_SW_MUTEX_GRANT, val); + + return id == I2C_SW_MUTEX_ID_CCPLEX; +} + +static bool tegra_i2c_mutex_trylock(struct tegra_i2c_dev *i2c_dev) +{ + unsigned int reg = tegra_i2c_reg_addr(i2c_dev, I2C_SW_MUTEX); + u32 val, id; + + val = readl(i2c_dev->base + reg); + id = FIELD_GET(I2C_SW_MUTEX_GRANT, val); + if (id != 0 && id != I2C_SW_MUTEX_ID_CCPLEX) + return false; + + val = FIELD_PREP(I2C_SW_MUTEX_REQUEST, I2C_SW_MUTEX_ID_CCPLEX); + writel(val, i2c_dev->base + reg); + + return tegra_i2c_mutex_acquired(i2c_dev); +} + +static int tegra_i2c_mutex_lock(struct tegra_i2c_dev *i2c_dev) +{ + bool locked; + int ret; + + if (!i2c_dev->hw->has_mutex) + return 0; + + if (i2c_dev->atomic_mode) + ret = read_poll_timeout_atomic(tegra_i2c_mutex_trylock, locked, locked, + USEC_PER_MSEC, I2C_SW_MUTEX_TIMEOUT_US, + false, i2c_dev); + else + ret = read_poll_timeout(tegra_i2c_mutex_trylock, locked, locked, USEC_PER_MSEC, + I2C_SW_MUTEX_TIMEOUT_US, false, i2c_dev); + + if (ret) + dev_warn(i2c_dev->dev, "failed to acquire mutex\n"); + + return ret; +} + +static int tegra_i2c_mutex_unlock(struct tegra_i2c_dev *i2c_dev) +{ + unsigned int reg = tegra_i2c_reg_addr(i2c_dev, I2C_SW_MUTEX); + u32 val, id; + + if (!i2c_dev->hw->has_mutex) + return 0; + + val = readl(i2c_dev->base + reg); + + id = FIELD_GET(I2C_SW_MUTEX_GRANT, val); + if (id && id != I2C_SW_MUTEX_ID_CCPLEX) { + dev_warn(i2c_dev->dev, "unable to unlock mutex, mutex is owned by: %u\n", id); + return -EPERM; + } + + writel(0, i2c_dev->base + reg); + + return 0; +} + static void tegra_i2c_mask_irq(struct tegra_i2c_dev *i2c_dev, u32 mask) { u32 int_mask;
@@ -1422,6 +1502,10 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], return ret; } + ret = tegra_i2c_mutex_lock(i2c_dev); + if (ret) + return ret; + for (i = 0; i < num; i++) { enum msg_end_type end_type = MSG_END_STOP;
@@ -1451,6 +1535,7 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], break; } + ret = tegra_i2c_mutex_unlock(i2c_dev); pm_runtime_put(i2c_dev->dev); return ret ?: i;
@@ -1527,6 +1612,7 @@ static const struct tegra_i2c_hw_feature tegra20_i2c_hw = { .setup_hold_time_hs_mode = 0x0, .has_interface_timing_reg = false, .has_hs_mode_support = false, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra30_i2c_hw = {
@@ -1553,6 +1639,7 @@ static const struct tegra_i2c_hw_feature tegra30_i2c_hw = { .setup_hold_time_hs_mode = 0x0, .has_interface_timing_reg = false, .has_hs_mode_support = false, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra114_i2c_hw = {
@@ -1579,6 +1666,7 @@ static const struct tegra_i2c_hw_feature tegra114_i2c_hw = { .setup_hold_time_hs_mode = 0x0, .has_interface_timing_reg = false, .has_hs_mode_support = false, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra124_i2c_hw = {
@@ -1605,6 +1693,7 @@ static const struct tegra_i2c_hw_feature tegra124_i2c_hw = { .setup_hold_time_hs_mode = 0x0, .has_interface_timing_reg = true, .has_hs_mode_support = false, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra210_i2c_hw = {
@@ -1631,6 +1720,7 @@ static const struct tegra_i2c_hw_feature tegra210_i2c_hw = { .setup_hold_time_hs_mode = 0, .has_interface_timing_reg = true, .has_hs_mode_support = false, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra186_i2c_hw = {
@@ -1657,6 +1747,7 @@ static const struct tegra_i2c_hw_feature tegra186_i2c_hw = { .setup_hold_time_hs_mode = 0, .has_interface_timing_reg = true, .has_hs_mode_support = false, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra194_i2c_hw = {
@@ -1685,6 +1776,7 @@ static const struct tegra_i2c_hw_feature tegra194_i2c_hw = { .setup_hold_time_hs_mode = 0x090909, .has_interface_timing_reg = true, .has_hs_mode_support = true, + .has_mutex = false, }; static const struct tegra_i2c_hw_feature tegra256_i2c_hw = {
--
2.43.0