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drivers: smbus: provide packet-error-checking (pec) routines
In the case that SMBus hardware does not automatically perform packet error checking (PEC), provide generic inline functions in `zephyr/drivers/smbus.h` that can be used by drivers to perform PEC in software. Signed-off-by: Chris Friedt <[email protected]> Signed-off-by: Andrew Lewycky <[email protected]>
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‎drivers/smbus/Kconfig‎

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@@ -5,6 +5,7 @@
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menuconfig SMBUS
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bool "System Management Bus (SMBus) drivers"
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imply CRC
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help
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Enable SMBus Driver Configuration
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‎drivers/smbus/smbus_utils.c‎

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@@ -7,6 +7,9 @@
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#include "smbus_utils.h"
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#include <zephyr/logging/log.h>
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#include <zephyr/sys/__assert.h>
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#include <zephyr/sys/crc.h>
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#include <zephyr/sys/util.h>
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LOG_MODULE_REGISTER(smbus_utils, CONFIG_SMBUS_LOG_LEVEL);
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@@ -41,3 +44,71 @@ void smbus_loop_alert_devices(const struct device *dev, sys_slist_t *callbacks)
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smbus_fire_callbacks(callbacks, dev, address);
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}
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}
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uint8_t smbus_pec_num_msgs(uint32_t flags, uint8_t num_msgs)
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{
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__ASSERT_NO_MSG(num_msgs != 0);
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if ((flags & SMBUS_MODE_PEC) == 0) {
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return num_msgs - 1;
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}
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return num_msgs;
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}
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uint8_t smbus_pec(uint16_t addr, const struct i2c_msg *msgs, uint8_t num_msgs)
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{
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uint8_t pec = 0;
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uint8_t prior_direction = 0;
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uint8_t addr8 = addr & BIT_MASK(7);
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for (uint8_t i = 0; i < num_msgs; i++) {
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/* When direction changes, there is a repeated start byte. */
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uint8_t start_byte;
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uint8_t direction = msgs[i].flags & I2C_MSG_RW_MASK;
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if ((i == 0) || (direction != prior_direction)) {
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prior_direction = direction;
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start_byte = (addr8 << 1) | direction;
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pec = crc8_ccitt(pec, &start_byte, sizeof(start_byte));
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}
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pec = crc8_ccitt(pec, msgs[i].buf, msgs[i].len);
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}
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return pec;
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}
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void smbus_write_prepare_pec(uint32_t flags, uint16_t addr, struct i2c_msg *msgs, uint8_t num_msgs)
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{
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if ((flags & SMBUS_MODE_PEC) == 0) {
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return;
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}
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__ASSERT_NO_MSG(msgs != NULL);
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__ASSERT_NO_MSG(num_msgs != 0);
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__ASSERT_NO_MSG(msgs[num_msgs - 1].buf != NULL);
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msgs[num_msgs - 1].buf[0] = smbus_pec(addr, msgs, num_msgs - 1);
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}
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int smbus_read_check_pec(uint32_t flags, uint16_t addr, const struct i2c_msg *msgs,
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uint8_t num_msgs)
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{
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if ((flags & SMBUS_MODE_PEC) == 0) {
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return 0;
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}
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__ASSERT_NO_MSG(num_msgs != 0);
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__ASSERT_NO_MSG(msgs != NULL);
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__ASSERT_NO_MSG(msgs[num_msgs - 1].buf != NULL);
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uint8_t reported_pec = msgs[num_msgs - 1].buf[0];
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uint8_t computed_pec = smbus_pec(addr, msgs, num_msgs - 1);
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if (reported_pec != computed_pec) {
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return -EIO;
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}
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return 0;
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}

‎drivers/smbus/smbus_utils.h‎

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@@ -7,8 +7,11 @@
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#ifndef ZEPHYR_DRIVERS_SMBUS_SMBUS_UTILS_H_
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#define ZEPHYR_DRIVERS_SMBUS_SMBUS_UTILS_H_
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#include <errno.h>
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#include <stdint.h>
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#include <zephyr/device.h>
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#include <zephyr/drivers/i2c.h>
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#include <zephyr/drivers/smbus.h>
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#include <zephyr/sys/slist.h>
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@@ -107,4 +110,82 @@ static inline void smbus_init_callback(struct smbus_callback *callback,
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*/
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void smbus_loop_alert_devices(const struct device *dev, sys_slist_t *callbacks);
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/**
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* @brief Compute the number of messages required for an SMBus transaction
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*
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* If @p flags indicates that the transaction requires packet error checking (PEC),
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* the number of messages is equal to @p num_msgs, otherwise the number of messages
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* required is @p num_msgs - 1, since a PEC byte is not required.
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*
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* Callers are expected to allocated an array of @ref i2c_msg objects to hold a number of
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* i2c messages, including one message dedicated to the a PEC byte, whether or not PEC is
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* being used.
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*
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* @note This function is intended for SMBus drivers that do not have hardware PEC support and
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* therefore must rely on software PEC calculation.
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*
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* @param flags SMBus flags.
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* @param num_msgs Number of allocated messages.
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* @return The number of required messages.
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*/
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uint8_t smbus_pec_num_msgs(uint32_t flags, uint8_t num_msgs);
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/**
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* @brief Compute the packet error checking (PEC) byte for an SMBus transaction
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*
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* @note This function is intended for SMBus drivers that do not have hardware PEC support and
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* therefore must rely on software PEC calculation.
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*
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* @note At this time, only 7-bit addresses are supported in @p addr.
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*
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* @param addr The address of the target device.
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* @param msgs Array of @ref i2c_msg that make up the transaction.
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* @param num_msgs Number of messages in the transaction.
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* @return the computed PEC byte.
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*/
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uint8_t smbus_pec(uint16_t addr, const struct i2c_msg *msgs, uint8_t num_msgs);
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/**
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* @brief Prepare the packet error checking (PEC) byte for an SMBus write transaction
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*
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* If the @p flags bitmask contains @ref SMBUS_MODE_PEC (i.e. PEC is enabled), the number of
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* messages is equal to @p num_msgs, otherwise the number of messages required is @p num_msgs - 1,
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* since a PEC byte is not required.
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*
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* @note This function is intended for SMBus drivers that do not have hardware PEC support and
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* therefore must rely on software PEC calculation.
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*
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* @note At this time, only 7-bit addresses are supported in @p addr.
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*
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* @param flags SMBus flags.
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* @param addr The address of the target device.
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* @param messages Array of @ref i2c_msg objects that make up the transaction.
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* @param num_msgs Number of messages in the transaction.
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*/
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void smbus_write_prepare_pec(uint32_t flags, uint16_t addr, struct i2c_msg *msgs, uint8_t num_msgs);
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/**
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* @brief Check the packet error checking (PEC) byte for an SMBus read transaction
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*
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* If the @p flags bitmask contains @ref SMBUS_MODE_PEC (i.e. PEC is enabled), the number of
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* messages is equal to @p num_msgs, otherwise the number of messages required is
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* @p num_msgs - 1, since a PEC byte is not required.
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*
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* When PEC is not enabled, this function returns 0.
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*
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* @note This function is intended for SMBus drivers that do not have hardware PEC support and
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* therefore must rely on software PEC calculation.
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*
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* @note At this time, only 7-bit addresses are supported in @p addr.
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*
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* @param flags SMBus flags.
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* @param addr The address of the target device.
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* @param messages Array of @ref i2c_msg objects that make up the transaction.
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* @param num_msgs Number of messages in the transaction.
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* @retval 0 on success.
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* @retval -EIO if the PEC byte does not match the computed value.
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*/
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int smbus_read_check_pec(uint32_t flags, uint16_t addr, const struct i2c_msg *msgs,
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uint8_t num_msgs);
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#endif /* ZEPHYR_DRIVERS_SMBUS_SMBUS_UTILS_H_ */

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