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

Mon Aug 3 09:27:28 EDT 2020

On 02.08.2020 19:54, Wolfram Sang wrote:
> 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 <codrin.ciubotariu at microchip.com>
> 
> 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.

Agree

> 
>>   	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/ ?

OK

> 
>> +	 */
>> +	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.

since default state is missing, the next check can be skipped, but I 
agree that removing the label makes things easier to read.

> 
>> +		}
>> +	}
>> +	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...

right

> 
>> +		}
>> +	}
>> +
>> +cleanup_pinctrl:
> 
> ... and this label can go then. Also nicer to read, I'd say.

I will remove it.

> 
>> +	/* 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.

Right, sorry about this. Will fix.

> 
>> +	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 :)

It is not the same thing. Without the first check, it will return 0 if
bri->recover_bus is NULL, which is not what we want. If bri->recover_bus 
is NULL (and the pintrl states and gpios are in place) we can set 
recover_bus to i2c_generic_scl_recovery and use the generic recovery.

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

OK

> 
>> +	 * 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);

I agree. I will add it.

> 
>> +
>> +	/* 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.
> 

I agree will all your suggestions, except with the removal of if 
(bri->recover_bus) . If you agree with this, I can send the next version 
and remove the RFC.

Thanks and best regards,
Codrin