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

Krzysztof Kozlowski
2023-10-27T11:27:48Z

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@alliedtelesis.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