[PATCH] i2c: gpio: Add custom deblock sequence

[Heiko Schocher]

Hello Marek,

Am 24.01.2020 um 19:12 schrieb Marek Vasut:
> Add custom deblock dequence for the I2C bus, needed on some devices.
> This sequence is issued once, when probing the driver, and is controlled
> by DT property, "i2c-gpio,deblock".
> 
> Signed-off-by: Marek Vasut <marex at denx.de>
> ---
>   drivers/i2c/i2c-gpio.c | 67 ++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 67 insertions(+)
> 
> diff --git a/drivers/i2c/i2c-gpio.c b/drivers/i2c/i2c-gpio.c
> index 4e8fa21473..46975ef5c8 100644
> --- a/drivers/i2c/i2c-gpio.c
> +++ b/drivers/i2c/i2c-gpio.c
> @@ -39,6 +39,11 @@ static int i2c_gpio_sda_get(struct gpio_desc *sda)
>   	return dm_gpio_get_value(sda);
>   }
>   
> +static int i2c_gpio_scl_get(struct gpio_desc *scl)
> +{
> +	return dm_gpio_get_value(scl);
> +}
> +
>   static void i2c_gpio_sda_set(struct gpio_desc *sda, int bit)
>   {
>   	if (bit)
> @@ -305,6 +310,67 @@ static int i2c_gpio_set_bus_speed(struct udevice *dev, unsigned int speed_hz)
>   	return 0;
>   }
>   
> +/*
> + * I2C is a synchronous protocol and resets of the processor in the middle
> + * of an access can block the I2C Bus until a powerdown of the full unit is
> + * done. This function toggles the SCL until the SCL and SCA line are
> + * released, but max. 16 times, after this a I2C start-sequence is sent.
> + * This I2C Deblocking mechanism was developed by Keymile in association
> + * with Anatech and Atmel in 1998.
> + */
> +static void i2c_gpio_make_abort(struct udevice *dev)
> +{
> +	struct i2c_gpio_bus *bus = dev_get_priv(dev);
> +	struct gpio_desc *scl = &bus->gpios[PIN_SCL];
> +	struct gpio_desc *sda = &bus->gpios[PIN_SDA];
> +	int scl_state = 0;
> +	int sda_state = 0;
> +	int i = 0;
> +	int ret = 0;
> +
> +#define DELAY_ABORT_SEQ	62	/* @200kHz 9 clocks = 44us, 62us is ok */
> +
> +	i2c_gpio_scl_set(scl, 1);
> +
> +	if (!i2c_gpio_sda_get(sda)) {
> +		ret = -1;
> +		for (i = 0; i < 16; i++) {
> +			i2c_gpio_scl_set(scl, 0);
> +			udelay(DELAY_ABORT_SEQ);
> +			i2c_gpio_scl_set(scl, 1);
> +			udelay(DELAY_ABORT_SEQ);
> +			scl_state = i2c_gpio_scl_get(scl);
> +			sda_state = i2c_gpio_sda_get(sda);
> +			if (scl_state && sda_state) {
> +				ret = 0;
> +				break;
> +			}
> +		}
> +	}
> +
> +	if (!ret) {
> +		for (i = 0; i < 5; i++) {
> +			i2c_gpio_send_start(scl, sda, 2 * bus->udelay);
> +			i2c_gpio_scl_set(scl, 0);
> +		}
> +	}
> +
> +	/* respect stop setup time */
> +	udelay(DELAY_ABORT_SEQ);
> +	i2c_gpio_scl_set(scl, 1);
> +	udelay(DELAY_ABORT_SEQ);
> +	i2c_gpio_sda_set(sda, 1);
> +	i2c_gpio_sda_get(sda);
> +}
> +
> +static int i2c_gpio_drv_probe(struct udevice *dev)
> +{
> +	if (dev_read_bool(dev, "i2c-gpio,deblock"))
> +		i2c_gpio_make_abort(dev);
> +
> +	return 0;
> +}
> +
>   static int i2c_gpio_ofdata_to_platdata(struct udevice *dev)
>   {
>   	struct i2c_gpio_bus *bus = dev_get_priv(dev);
> @@ -341,6 +407,7 @@ U_BOOT_DRIVER(i2c_gpio) = {
>   	.name	= "i2c-gpio",
>   	.id	= UCLASS_I2C,
>   	.of_match = i2c_gpio_ids,
> +	.probe	= i2c_gpio_drv_probe,
>   	.ofdata_to_platdata = i2c_gpio_ofdata_to_platdata,
>   	.priv_auto_alloc_size = sizeof(struct i2c_gpio_bus),
>   	.ops	= &i2c_gpio_ops,
> 

Hmm.. why do you add this into the probe function and do not add
it to:

https://gitlab.denx.de/u-boot/u-boot/blob/master/include/i2c.h#L382

which is called from:
https://gitlab.denx.de/u-boot/u-boot/blob/master/drivers/i2c/i2c-uclass.c#L586


Ok, i2c_deblock() currently is only used from do_i2c_reset(), but may it
is worth to adapt drivers/i2c-core/i2c-uclass.c to call the deblock
sequence also from i2c_pre_probe()?

May dependend on your proposed DT property "i2c-gpio,deblock" ?

But please update also the documentation in

u-boot:/doc/device-tree-bindings/i2c/i2c-gpio.txt

or if we go the more generic way:

u-boot:/doc/device-tree-bindings/i2c/i2c.txt

Thanks!

BTW: May it makes sense to adapt:
https://gitlab.denx.de/u-boot/u-boot/blob/master/drivers/i2c/i2c-uclass.c#L504

too?

bye,
Heiko
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