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Date:   Wed, 29 Jul 2020 03:11:21 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Mark Tomlinson <Mark.Tomlinson@...iedtelesis.co.nz>,
        "gregory.clement@...tlin.com" <gregory.clement@...tlin.com>
CC:     "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: mv64xxx: Add bus error recovery

Hi Mark,

On 8/07/20 9:10 am, Mark Tomlinson wrote:
> This adds i2c bus recovery to the mv64xxx driver.
>
> Implement bus recovery to recover from SCL/SDA stuck low.
>
> This uses the generic recovery function, setting the clock/data lines as
> GPIO pins, and sending 9 clocks to try and recover the bus.
>
> Signed-off-by: Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>

Reviewed-by: Chris Packham <chris.packham@...iedtelesis.co.nz>

One additional comment below

> ---
>   drivers/i2c/busses/i2c-mv64xxx.c | 77 +++++++++++++++++++++++++++++++-
>   1 file changed, 76 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
> index 829b8c98ae51..e58853ba3ef0 100644
> --- a/drivers/i2c/busses/i2c-mv64xxx.c
> +++ b/drivers/i2c/busses/i2c-mv64xxx.c
> @@ -21,6 +21,7 @@
>   #include <linux/io.h>
>   #include <linux/of.h>
>   #include <linux/of_device.h>
> +#include <linux/of_gpio.h>
>   #include <linux/of_irq.h>
>   #include <linux/clk.h>
>   #include <linux/err.h>
> @@ -147,6 +148,10 @@ struct mv64xxx_i2c_data {
>   	bool			irq_clear_inverted;
>   	/* Clk div is 2 to the power n, not 2 to the power n + 1 */
>   	bool			clk_n_base_0;
> +	struct pinctrl		*pinctrl;
> +	struct i2c_bus_recovery_info	rinfo;
> +	struct pinctrl_state	*pin_default_state;
> +	struct pinctrl_state	*pin_gpio_state;
>   };
>   
>   static struct mv64xxx_i2c_regs mv64xxx_i2c_regs_mv64xxx = {
> @@ -325,7 +330,8 @@ mv64xxx_i2c_fsm(struct mv64xxx_i2c_data *drv_data, u32 status)
>   			 drv_data->msg->flags);
>   		drv_data->action = MV64XXX_I2C_ACTION_SEND_STOP;
>   		mv64xxx_i2c_hw_init(drv_data);
> -		drv_data->rc = -EIO;
> +		i2c_recover_bus(&drv_data->adapter);
> +		drv_data->rc = -EAGAIN;
>   	}
>   }
>   
> @@ -563,6 +569,7 @@ mv64xxx_i2c_wait_for_completion(struct mv64xxx_i2c_data *drv_data)
>   				"time_left: %d\n", drv_data->block,
>   				(int)time_left);
>   			mv64xxx_i2c_hw_init(drv_data);
> +			i2c_recover_bus(&drv_data->adapter);
>   		}
>   	} else
>   		spin_unlock_irqrestore(&drv_data->lock, flags);
> @@ -872,6 +879,69 @@ mv64xxx_of_config(struct mv64xxx_i2c_data *drv_data,
>   }
>   #endif /* CONFIG_OF */
>   
> +/*
> + * Switch to bit bang mode to prepare for i2c generic recovery.
> + */
> +static void mv64xxx_i2c_prepare_recovery(struct i2c_adapter *adap)
> +{
> +	struct mv64xxx_i2c_data *drv_data = i2c_get_adapdata(adap);
> +
> +	pinctrl_select_state(drv_data->pinctrl, drv_data->pin_gpio_state);
> +}
> +
> +/*
> + * Return to normal i2c operation following recovery.
> + */
> +static void mv64xxx_i2c_unprepare_recovery(struct i2c_adapter *adap)
> +{
> +	struct mv64xxx_i2c_data *drv_data = i2c_get_adapdata(adap);
> +
> +	pinctrl_select_state(drv_data->pinctrl, drv_data->pin_default_state);
> +}
> +
> +static int mv64xxx_i2c_init_recovery_info(struct mv64xxx_i2c_data *drv_data,
> +					  struct platform_device *pd)
> +{
> +	struct i2c_bus_recovery_info *rinfo = &drv_data->rinfo;
> +	struct device *dev = &pd->dev;
> +
> +	drv_data->pinctrl = devm_pinctrl_get(dev);
> +	if (!drv_data->pinctrl || IS_ERR(drv_data->pinctrl)) {
> +		dev_err(dev, "can't get pinctrl, bus recovery not supported\n");
> +		return PTR_ERR(drv_data->pinctrl);
> +	}
> +
> +	drv_data->pin_default_state = pinctrl_lookup_state(drv_data->pinctrl,
> +			PINCTRL_STATE_DEFAULT);
> +	drv_data->pin_gpio_state = pinctrl_lookup_state(drv_data->pinctrl,
> +			"gpio");
> +	rinfo->scl_gpiod = devm_gpiod_get(dev, "scl",
> +					  GPIOD_OUT_HIGH_OPEN_DRAIN);
> +	rinfo->sda_gpiod = devm_gpiod_get(dev, "sda", GPIOD_IN);

Should these be mentioned in 
Documentation/devicetree/bindings/i2c/marvell,mv64xxx-i2c.yaml?

> +	if (PTR_ERR(rinfo->scl_gpiod) == -EPROBE_DEFER ||
> +	    PTR_ERR(rinfo->sda_gpiod) == -EPROBE_DEFER)
> +		return -EPROBE_DEFER;
> +
> +	if (IS_ERR(rinfo->sda_gpiod) ||
> +	    IS_ERR(rinfo->scl_gpiod) ||
> +	    IS_ERR(drv_data->pin_default_state) ||
> +	    IS_ERR(drv_data->pin_gpio_state)) {
> +		dev_dbg(dev, "recovery information incomplete\n");
> +		return 0;
> +	}
> +
> +	dev_dbg(dev, "using scl-gpio %d and sda-gpio %d for recovery\n",
> +		rinfo->scl_gpiod ? desc_to_gpio(rinfo->scl_gpiod) : -1,
> +		rinfo->sda_gpiod ? desc_to_gpio(rinfo->sda_gpiod) : -1);
> +
> +	rinfo->prepare_recovery = mv64xxx_i2c_prepare_recovery;
> +	rinfo->unprepare_recovery = mv64xxx_i2c_unprepare_recovery;
> +	rinfo->recover_bus = i2c_generic_scl_recovery;
> +	drv_data->adapter.bus_recovery_info = rinfo;
> +
> +	return 0;
> +}
> +
>   static int
>   mv64xxx_i2c_probe(struct platform_device *pd)
>   {
> @@ -939,6 +1009,10 @@ mv64xxx_i2c_probe(struct platform_device *pd)
>   
>   	mv64xxx_i2c_hw_init(drv_data);
>   
> +	rc = mv64xxx_i2c_init_recovery_info(drv_data, pd);
> +	if (rc == -EPROBE_DEFER)
> +		goto exit_reset;
> +
>   	rc = request_irq(drv_data->irq, mv64xxx_i2c_intr, 0,
>   			 MV64XXX_I2C_CTLR_NAME, drv_data);
>   	if (rc) {
> @@ -951,6 +1025,7 @@ mv64xxx_i2c_probe(struct platform_device *pd)
>   			"mv64xxx: Can't add i2c adapter, rc: %d\n", -rc);
>   		goto exit_free_irq;
>   	}
> +	i2c_recover_bus(&drv_data->adapter);
>   
>   	return 0;
>   

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