From 6d49edd9a348b2d6549dac420152d30aeb970953 Mon Sep 17 00:00:00 2001 From: Aniket Randive Date: Fri, 11 Sep 2026 12:29:51 +0530 Subject: i2c: core: Add i2c_update_timeout() helper for dynamic transfer timeouts The transfer timeout for an I2C controller should reflect the actual message length and bus frequency rather than a static 1-second value. A static timeout causes unnecessary delays on error paths for short messages, and may be insufficient for very long transfers. Add i2c_update_timeout() to i2c-core which computes a transfer-specific timeout and stores it directly in the standard adap->timeout field. The formula accounts for 9 bits per byte (8 data + 1 ACK) at the configured bus frequency. The caller supplies a safety multiplier and a minimum floor so that each driver retains full control over its timing policy without those values becoming public API. Storing the result in adap->timeout makes it visible to all consumers of that field, including the arbitration-loss retry loop in __i2c_transfer(). The function is gated by CONFIG_I2C_DYNAMIC_TIMEOUT. When the config is disabled, i2c_update_timeout() compiles to a no-op inline stub so drivers that call it build cleanly and the existing static 1-second default is preserved unchanged. A timeout explicitly configured by userspace via the I2C_TIMEOUT ioctl is stored in a new adap->user_timeout field and always takes precedence over the kernel-computed value. When userspace has not configured a timeout, the computed value is used. The ioctl keeps writing adap->timeout as well, so adapters that never call i2c_update_timeout() continue to honour it exactly as before. As i2c_update_timeout() is an exported helper, guard against a zero bus frequency from a misbehaving caller with WARN_ON_ONCE() and return early, leaving the existing timeout untouched as a safe fallback rather than dividing by zero. Signed-off-by: Aniket Randive Reviewed-by: Mukesh Kumar Savaliya Signed-off-by: Andi Shyti Link: https://patch.msgid.link/20260911-master-v9-1-77ac458344e2@oss.qualcomm.com --- include/linux/i2c.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'include/linux') diff --git a/include/linux/i2c.h b/include/linux/i2c.h index f3192ab1982e..6a847fc88d25 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h @@ -757,6 +757,9 @@ struct i2c_adapter { struct rt_mutex mux_lock; int timeout; /* in jiffies */ +#ifdef CONFIG_I2C_DYNAMIC_TIMEOUT + int user_timeout; /* I2C_TIMEOUT ioctl value in jiffies */ +#endif int retries; struct device dev; /* the adapter device */ unsigned long locked_flags; /* owned by the I2C core */ @@ -928,6 +931,16 @@ unsigned int i2c_adapter_depth(struct i2c_adapter *adapter); void i2c_parse_fw_timings(struct device *dev, struct i2c_timings *t, bool use_defaults); +#ifdef CONFIG_I2C_DYNAMIC_TIMEOUT +void i2c_update_timeout(struct i2c_adapter *adap, u32 bus_freq_hz, + size_t len, unsigned int safety_coeff, + unsigned int min_usec); +#else +static inline void i2c_update_timeout(struct i2c_adapter *adap, u32 bus_freq_hz, + size_t len, unsigned int safety_coeff, + unsigned int min_usec) {} +#endif + /* Return the functionality mask */ static inline u32 i2c_get_functionality(struct i2c_adapter *adap) { -- cgit v1.2.3