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- From f11a04464ae57e8db1bb7634547842b43e36a898 Mon Sep 17 00:00:00 2001
- From: =?UTF-8?q?Jan=20Kundr=C3=A1t?= <jan.kundrat@cesnet.cz>
- Date: Fri, 22 Dec 2017 22:47:16 +0100
- Subject: i2c: gpio: Enable working over slow can_sleep GPIOs
- MIME-Version: 1.0
- Content-Type: text/plain; charset=UTF-8
- Content-Transfer-Encoding: 8bit
- "Slow" GPIOs (usually those connected over an SPI or an I2C bus) are,
- well, slow in their operation. It is generally a good idea to avoid
- using them for time-critical operation, but sometimes the hardware just
- sucks, and the software has to cope. In addition to that, the I2C bus
- itself does not actually define any strict timing limits; the bus is
- free to go all the way down to DC. The timeouts (and therefore the
- slowest acceptable frequency) are present only in SMBus.
- The `can_sleep` is IMHO a wrong concept to use here. My SPI-to-quad-UART
- chip (MAX14830) is connected via a 26MHz SPI bus, and it happily drives
- SCL at 200kHz (5µs pulses) during my benchmarks. That's faster than the
- maximal allowed speed of the traditional I2C.
- The previous version of this code did not really block operation over
- slow GPIO pins, anyway. Instead, it just resorted to printing a warning
- with a backtrace each time a GPIO pin was accessed, thereby slowing
- things down even more.
- Finally, it's not just me. A similar patch was originally submitted in
- 2015 [1].
- [1] https://patchwork.ozlabs.org/patch/450956/
- Signed-off-by: Jan Kundrát <jan.kundrat@cesnet.cz>
- Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
- Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
- ---
- drivers/i2c/busses/i2c-gpio.c | 11 +++++++----
- 1 file changed, 7 insertions(+), 4 deletions(-)
- --- a/drivers/i2c/busses/i2c-gpio.c
- +++ b/drivers/i2c/busses/i2c-gpio.c
- @@ -44,7 +44,7 @@ static void i2c_gpio_setsda_val(void *da
- {
- struct i2c_gpio_platform_data *pdata = data;
-
- - gpio_set_value(pdata->sda_pin, state);
- + gpio_set_value_cansleep(pdata->sda_pin, state);
- }
-
- /* Toggle SCL by changing the direction of the pin. */
- @@ -68,21 +68,21 @@ static void i2c_gpio_setscl_val(void *da
- {
- struct i2c_gpio_platform_data *pdata = data;
-
- - gpio_set_value(pdata->scl_pin, state);
- + gpio_set_value_cansleep(pdata->scl_pin, state);
- }
-
- static int i2c_gpio_getsda(void *data)
- {
- struct i2c_gpio_platform_data *pdata = data;
-
- - return gpio_get_value(pdata->sda_pin);
- + return gpio_get_value_cansleep(pdata->sda_pin);
- }
-
- static int i2c_gpio_getscl(void *data)
- {
- struct i2c_gpio_platform_data *pdata = data;
-
- - return gpio_get_value(pdata->scl_pin);
- + return gpio_get_value_cansleep(pdata->scl_pin);
- }
-
- static int of_i2c_gpio_get_pins(struct device_node *np,
- @@ -175,6 +175,9 @@ static int i2c_gpio_probe(struct platfor
- memcpy(pdata, dev_get_platdata(&pdev->dev), sizeof(*pdata));
- }
-
- + if (gpiod_cansleep(gpio_to_desc(pdata->sda_pin)) || gpiod_cansleep(gpio_to_desc(pdata->scl_pin)))
- + dev_warn(&pdev->dev, "Slow GPIO pins might wreak havoc into I2C/SMBus bus timing");
- +
- if (pdata->sda_is_open_drain) {
- gpio_direction_output(pdata->sda_pin, 1);
- bit_data->setsda = i2c_gpio_setsda_val;
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