linux-kernel - Re: [PATCH v3 2/2] i2c: mv64xxx: add an optional reset-gpios property

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Date:   Tue, 24 Oct 2023 08:15:00 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     "gregory.clement@...tlin.com" <gregory.clement@...tlin.com>,
        "andi.shyti@...nel.org" <andi.shyti@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>
CC:     "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] i2c: mv64xxx: add an optional reset-gpios property


On 19/10/23 10:08, Chris Packham wrote:
> Some hardware designs have a GPIO used to control the reset of all the
> devices on and I2C bus. It's not possible for every child node to
> declare a reset-gpios property as only the first device probed would be
> able to successfully request it (the others will get -EBUSY). Represent
> this kind of hardware design by associating the reset-gpios with the
> parent I2C bus. The reset line will be released prior to the child I2C
> devices being probed.
>
> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> ---
>
> Notes:
>      Changes in v3:
>      - Rename reset-delay to reset-duration
>      - Use reset-duration-us property to control the reset pulse rather than
>        delaying after the reset
>      Changes in v2:
>      - Add a property to cover the length of delay after releasing the reset
>        GPIO
>      - Use dev_err_probe() when requesing the GPIO fails
>
>   drivers/i2c/busses/i2c-mv64xxx.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
> index efd28bbecf61..28f11d2e800b 100644
> --- a/drivers/i2c/busses/i2c-mv64xxx.c
> +++ b/drivers/i2c/busses/i2c-mv64xxx.c

kernel test robot points out I'm missing an include of gpio/consumer.h 
I'll fix that with a v4. I'll give it a couple of days before sending it 
out just in case there are any more comments.

> @@ -160,6 +160,7 @@ struct mv64xxx_i2c_data {
>   	bool			clk_n_base_0;
>   	struct i2c_bus_recovery_info	rinfo;
>   	bool			atomic;
> +	struct gpio_desc	*reset_gpio;
>   };
>   
>   static struct mv64xxx_i2c_regs mv64xxx_i2c_regs_mv64xxx = {
> @@ -1036,6 +1037,7 @@ mv64xxx_i2c_probe(struct platform_device *pd)
>   	struct mv64xxx_i2c_data		*drv_data;
>   	struct mv64xxx_i2c_pdata	*pdata = dev_get_platdata(&pd->dev);
>   	struct resource *res;
> +	u32	reset_duration;
>   	int	rc;
>   
>   	if ((!pdata && !pd->dev.of_node))
> @@ -1083,6 +1085,14 @@ mv64xxx_i2c_probe(struct platform_device *pd)
>   	if (drv_data->irq < 0)
>   		return drv_data->irq;
>   
> +	drv_data->reset_gpio = devm_gpiod_get_optional(&pd->dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(drv_data->reset_gpio))
> +		return dev_err_probe(&pd->dev, PTR_ERR(drv_data->reset_gpio),
> +				     "Cannot get reset gpio\n");
> +	rc = device_property_read_u32(&pd->dev, "reset-duration-us", &reset_duration);
> +	if (rc)
> +		reset_duration = 1;
> +
>   	if (pdata) {
>   		drv_data->freq_m = pdata->freq_m;
>   		drv_data->freq_n = pdata->freq_n;
> @@ -1121,6 +1131,11 @@ mv64xxx_i2c_probe(struct platform_device *pd)
>   			goto exit_disable_pm;
>   	}
>   
> +	if (drv_data->reset_gpio) {
> +		usleep_range(reset_duration, reset_duration + 10);
> +		gpiod_set_value_cansleep(drv_data->reset_gpio, 0);
> +	}
> +
>   	rc = request_irq(drv_data->irq, mv64xxx_i2c_intr, 0,
>   			 MV64XXX_I2C_CTLR_NAME, drv_data);
>   	if (rc) {