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

> 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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