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drivers: i2c: esp32: set timeout to allow clock stretching

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The ESP32 series MCUs allow to set a timeout which triggers an error
if the SCL line is unchanged for the specified amount of time.

By default, the ESP-IDF HAL sets the timeout to an arbitrary value of
10 times the bus cycle.

This is not sufficient for chips like the TI bq76952, which pulls the
SCL line low (clock stretching) for several 100 µs.

The timeout should also not be dependent on the chosen bitrate, as it
is defined by the time a chip needs for internal calculation before it
can provide requested data or continue communication.

This commit adds a property to devicetree to allow configuration of
the scl timeout. This value is set via direct register access, as the
ESP-IDF HAL does not provide access to the enable bit and does not
give any information about the maximum size of the timeout (defined
in I2C clock cycles in the register).

Fixes #51351

Signed-off-by: Martin Jäger <martin@libre.solar>
This commit is contained in:
Martin Jäger 2022-10-18 19:03:54 +02:00 committed by Stephanos Ioannidis
parent 1529968884
commit d5168a8d96
2 changed files with 38 additions and 0 deletions
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28
drivers/i2c/i2c_esp32.c
View file

@ -91,6 +91,7 @@ struct i2c_esp32_config {
const uint32_t default_config;
const uint32_t bitrate;
const uint32_t scl_timeout;
};
/* I2C clock characteristic, The order is the same as i2c_sclk_t. */
@ -238,6 +239,27 @@ static int i2c_esp32_recover(const struct device *dev)
return 0;
}
static void IRAM_ATTR i2c_esp32_configure_timeout(const struct device *dev)
{
const struct i2c_esp32_config *config = dev->config;
if (config->scl_timeout > 0) {
i2c_sclk_t sclk = i2c_get_clk_src(config->bitrate);
uint32_t clk_freq_mhz = I2C_LL_CLK_SRC_FREQ(sclk);
uint32_t timeout_cycles = MIN(I2C_TIME_OUT_REG_V,
clk_freq_mhz / MHZ(1) * config->scl_timeout);
sys_clear_bits(I2C_TO_REG(config->index), I2C_TIME_OUT_REG);
sys_set_bits(I2C_TO_REG(config->index), timeout_cycles << I2C_TIME_OUT_REG_S);
LOG_DBG("SCL timeout: %d us, value: %d", config->scl_timeout, timeout_cycles);
} else {
/* Disabling the timeout by clearing the I2C_TIME_OUT_EN bit does not seem to work,
* at least for ESP32-C3 (tested with communication to bq76952 chip). So we set the
* timeout to maximum supported value instead.
*/
sys_set_bits(I2C_TO_REG(config->index), I2C_TIME_OUT_REG);
}
}
static int i2c_esp32_configure(const struct device *dev, uint32_t dev_config)
{
const struct i2c_esp32_config *config = dev->config;
@ -272,6 +294,7 @@ static int i2c_esp32_configure(const struct device *dev, uint32_t dev_config)
}
i2c_hal_set_bus_timing(&data->hal, config->bitrate, i2c_get_clk_src(config->bitrate));
i2c_esp32_configure_timeout(dev);
i2c_hal_update_config(&data->hal);
return 0;
@ -709,6 +732,10 @@ static int IRAM_ATTR i2c_esp32_init(const struct device *dev)
#define I2C_ESP32_GET_PIN_INFO(idx)
#endif /* SOC_I2C_SUPPORT_HW_CLR_BUS */
#define I2C_ESP32_TIMEOUT(inst) \
COND_CODE_1(DT_INST_NODE_HAS_PROP(inst, scl_timeout_us), \
(DT_INST_PROP(inst, scl_timeout_us)), (0))
#define I2C_ESP32_FREQUENCY(bitrate) \
(bitrate == I2C_BITRATE_STANDARD ? KHZ(100) \
: bitrate == I2C_BITRATE_FAST ? KHZ(400) \
@ -741,6 +768,7 @@ static int IRAM_ATTR i2c_esp32_init(const struct device *dev)
}, \
.irq_source = ETS_I2C_EXT##idx##_INTR_SOURCE, \
.bitrate = I2C_FREQUENCY(idx), \
.scl_timeout = I2C_ESP32_TIMEOUT(idx), \
.default_config = I2C_MODE_CONTROLLER, \
}; \
I2C_DEVICE_DT_DEFINE(I2C(idx), i2c_esp32_init, NULL, &i2c_esp32_data_##idx, \

10
dts/bindings/i2c/espressif,esp32-i2c.yaml
View file

@ -46,3 +46,13 @@ properties:
type: boolean
required: false
description: Set I2C RX data as LSB
scl-timeout-us:
type: int
required: false
description: |
Timeout for unchanged SCL during clock stretching of the I2C target in
microseconds.
If not set or 0, the timeout is disabled or set to the maximum possible
value if the MCU does not support disabling the timeout.