Subject: Re: [RFC PATCH 2/4] i2c: core: add generic I2C GPIO recovery

From: Wolfram Sang <[email-masked]>
Date: Sun, 2 Aug 2020 18:54:46 +0200

On Fri, Jun 19, 2020 at 05:19:02PM +0300, Codrin Ciubotariu wrote:
> Multiple I2C bus drivers use similar bindings to obtain information needed
> for I2C recovery. For example, for platforms using device-tree, the
> properties look something like this:
> 
> &i2c {
> 	...
> 	pinctrl-names = "default", "gpio";
> 	// or pinctrl-names = "default", "recovery";
> 	pinctrl-0 = <&pinctrl_i2c_default>;
> 	pinctrl-1 = <&pinctrl_i2c_gpio>;
> 	sda-gpios = <&pio 0 GPIO_ACTIVE_HIGH>;
> 	scl-gpios = <&pio 1 (GPIO_ACTIVE_HIGH | GPIO_OPEN_DRAIN)>;
> 	...
> }
> 
> For this reason, we can add this common initialization in the core. This
> way, other I2C bus drivers will be able to support GPIO recovery just by
> providing a pointer to platform's pinctrl and calling i2c_recover_bus()
> when SDA is stuck low.
> 
> Signed-off-by: Codrin Ciubotariu <[email-masked]>

Thanks, it looks a lot like what I had in mind!

> ---
>  drivers/i2c/i2c-core-base.c | 119 ++++++++++++++++++++++++++++++++++++
>  include/linux/i2c.h         |  11 ++++
>  2 files changed, 130 insertions(+)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index d1f278f73011..4ee29fec4e93 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -32,6 +32,7 @@
>  #include <linux/of_device.h>
>  #include <linux/of.h>
>  #include <linux/of_irq.h>
> +#include <linux/pinctrl/consumer.h>
>  #include <linux/pm_domain.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/pm_wakeirq.h>
> @@ -179,6 +180,8 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
>  	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
>  	int i = 0, scl = 1, ret = 0;
>  
> +	if (bri->pinctrl)
> +		pinctrl_select_state(bri->pinctrl, bri->pins_gpio);

I think this should come after 'prepare_recovery'. It may be that
'prepare_recovery' already needs to select the pinctrl state to avoid a
glitch. In this version, there would be a glitch then. If we move it
down, the doubled 'pinctrl_select_state' would be a noop then.

>  	if (bri->prepare_recovery)
>  		bri->prepare_recovery(adap);
>  
> @@ -236,6 +239,8 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
>  
>  	if (bri->unprepare_recovery)
>  		bri->unprepare_recovery(adap);
> +	if (bri->pinctrl)
> +		pinctrl_select_state(bri->pinctrl, bri->pins_default);

Here it is OK and will still work with the PXA version which needs to
select the state on its own.

>  
>  	return ret;
>  }
> @@ -251,6 +256,118 @@ int i2c_recover_bus(struct i2c_adapter *adap)
>  }
>  EXPORT_SYMBOL_GPL(i2c_recover_bus);
>  
> +static void i2c_gpio_init_pinctrl_recovery(struct i2c_adapter *adap)
> +{
> +	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
> +	struct device *dev = &adap->dev;
> +	struct pinctrl *p = bri->pinctrl;
> +
> +	/*
> +	 * we can't change states without pinctrl, so remove the states if
> +	 * available

s/available/populated/ ?

> +	 */
> +	if (!p) {
> +		bri->pins_default = NULL;
> +		bri->pins_gpio = NULL;
> +		return;
> +	}
> +
> +	if (!bri->pins_default) {
> +		bri->pins_default = pinctrl_lookup_state(p,
> +							 PINCTRL_STATE_DEFAULT);
> +		if (IS_ERR(bri->pins_default)) {
> +			dev_dbg(dev, PINCTRL_STATE_DEFAULT " state not found for GPIO recovery\n");
> +			bri->pins_default = NULL;
> +
> +			goto cleanup_pinctrl;

I'd leave out the goto here. It is OK to check both parameters, I think.

> +		}
> +	}
> +	if (!bri->pins_gpio) {
> +		bri->pins_gpio = pinctrl_lookup_state(p, "gpio");
> +		if (IS_ERR(bri->pins_gpio))
> +			bri->pins_gpio = pinctrl_lookup_state(p, "recovery");
> +
> +		if (IS_ERR(bri->pins_gpio)) {
> +			dev_dbg(dev, "no gpio or recovery state found for GPIO recovery\n");
> +			bri->pins_gpio = NULL;
> +
> +			goto cleanup_pinctrl;

This goto is not needed...

> +		}
> +	}
> +
> +cleanup_pinctrl:

... and this label can go then. Also nicer to read, I'd say.

> +	/* for pinctrl state changes, we need all the information */
> +	if (!bri->pins_default || !bri->pins_gpio) {
> +		bri->pinctrl = NULL;
> +		bri->pins_default = NULL;
> +		bri->pins_gpio = NULL;
> +	} else {
> +		dev_info(dev, "using pinctrl states for GPIO recovery");
> +	}
> +}
> +
> +static int i2c_gpio_init_generic_recovery(struct i2c_adapter *adap)
> +{
> +	struct i2c_bus_recovery_info *bri = adap->bus_recovery_info;
> +	struct device *dev = &adap->dev;
> +	struct gpio_desc *gpiod;
> +	int ret = 0;
> +
> +	/* don't touch the recovery information if the driver is not using
> +	 * generic SCL recovery
> +	 */

Not kernel comment style.

> +	if (bri->recover_bus && bri->recover_bus != i2c_generic_scl_recovery)
> +		return 0;

No need for the first condition. 'i2c_generic_scl_recovery' is
definately not NULL :)

> +
> +	/*
> +	 * pins might be taken as GPIO, so we might as well inform pinctrl about

s/might as well/should/

> +	 * this and move the state to GPIO
> +	 */
> +	if (bri->pinctrl)
> +		pinctrl_select_state(bri->pinctrl, bri->pins_gpio);
> +
> +	/*
> +	 * if there is incomplete or no recovery information, see if generic
> +	 * GPIO recovery is available
> +	 */
> +	if (!bri->scl_gpiod) {
> +		gpiod = devm_gpiod_get(dev, "scl", GPIOD_OUT_HIGH_OPEN_DRAIN);
> +		if (PTR_ERR(gpiod) == -EPROBE_DEFER) {
> +			ret  = -EPROBE_DEFER;
> +			goto cleanup_pinctrl_state;
> +		}
> +		if (!IS_ERR(gpiod)) {
> +			bri->scl_gpiod = gpiod;
> +			bri->recover_bus = i2c_generic_scl_recovery;
> +			dev_info(dev, "using generic GPIOs for recovery\n");
> +		}
> +	}

I think this extra code from the PXA driver makes sense in case SDA was
released while we were executing this code:

1383         /*
1384          * We have SCL. Pull SCL low and wait a bit so that SDA glitches
1385          * have no effect.
1386          */
1387         gpiod_direction_output(bri->scl_gpiod, 0);
1388         udelay(10);
1389         bri->sda_gpiod = devm_gpiod_get(dev, "sda", GPIOD_OUT_HIGH_OPEN_DRAIN);
1390 
1391         /* Wait a bit in case of a SDA glitch, and then release SCL. */
1392         udelay(10);
1393         gpiod_direction_output(bri->scl_gpiod, 1);

> +
> +	/* SDA GPIOD line is optional, so we care about DEFER only */
> +	if (!bri->sda_gpiod) {
> +		gpiod = devm_gpiod_get(dev, "sda", GPIOD_IN);
> +		if (PTR_ERR(gpiod) == -EPROBE_DEFER) {
> +			ret = -EPROBE_DEFER;
> +			goto cleanup_pinctrl_state;
> +		}
> +		if (!IS_ERR(gpiod))
> +			bri->sda_gpiod = gpiod;
> +	}
> +
> +cleanup_pinctrl_state:
> +	/* change the state of the pins back to their default state */
> +	if (bri->pinctrl)
> +		pinctrl_select_state(bri->pinctrl, bri->pins_default);
> +
> +	return ret;
> +}
> +

Rest looks good! If you have some time for this now, I will make sure to
get it into 5.9. With these minor things fixed, this is good to go, me
thinks.

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