linux-kernel - Re: [PATCH v5 2/2] i2c: mv64xxx: add an optional bus-reset-gpios property

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Message-ID: <65911ec0-e073-435f-846a-c5501dd5d3a9@linaro.org>
Date:   Fri, 27 Oct 2023 13:27:41 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Chris Packham <chris.packham@...iedtelesis.co.nz>,
        gregory.clement@...tlin.com, andi.shyti@...nel.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, Abel Vesa <abel.vesa@...aro.org>
Cc:     linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/2] i2c: mv64xxx: add an optional bus-reset-gpios
 property

On 27/10/2023 05:31, 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 bus-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 v5:
>     - Rename reset-gpios and reset-duration-us to bus-reset-gpios and
>       bus-reset-duration-us as requested by Wolfram
>     Changes in v4:
>     - Add missing gpio/consumer.h
>     - use fsleep() for enforcing reset-duration
>     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 | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
> index efd28bbecf61..6e2762d22e5a 100644
> --- a/drivers/i2c/busses/i2c-mv64xxx.c
> +++ b/drivers/i2c/busses/i2c-mv64xxx.c
> @@ -13,6 +13,7 @@
>  #include <linux/slab.h>
>  #include <linux/module.h>
>  #include <linux/spinlock.h>
> +#include <linux/gpio/consumer.h>
>  #include <linux/i2c.h>
>  #include <linux/interrupt.h>
>  #include <linux/mv643xx_i2c.h>
> @@ -160,6 +161,7 @@ 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 +1038,7 @@ 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 +1086,14 @@ 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, "bus-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, "bus-reset-duration-us", &reset_duration);
> +	if (rc)
> +		reset_duration = 1;

No, this should be solved by core - for entire I2C at minimum. This is
not specific to this device.

Best regards,
Krzysztof