Re: [PATCH v7 2/5] i3c: add sysfs attribute for device NACK retry

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 08/12/2025 15:11:17+0800, adrianhoyin.ng@altera.com wrote:
> From: Adrian Ng Ho Yin <adrianhoyin.ng@altera.com>
> 
> Add a `dev_nack_retry` sysfs attribute to allow reading and updating the
> device NACK retry count. A new `dev_nack_retry` field and an optional
> `set_dev_nack_retry()` callback are added to i3c_master_controller.
> The attribute is created only when the callback is implemented.
> 
> Updates are applied under the I3C bus maintenance lock to ensure safe
> hardware reconfiguration.
> 
> Signed-off-by: Adrian Ng Ho Yin <adrianhoyin.ng@altera.com>
> ---
>  drivers/i3c/master.c       | 38 ++++++++++++++++++++++++++++++++++++++
>  include/linux/i3c/master.h |  6 ++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index d946db75df70..2903725bee03 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -685,6 +685,38 @@ static ssize_t hotjoin_show(struct device *dev, struct device_attribute *da, cha
>  
>  static DEVICE_ATTR_RW(hotjoin);
>  
> +static ssize_t dev_nack_retry_show(struct device *dev, struct device_attribute *attr,
> +				   char *buf)
> +{
> +	return sysfs_emit(buf, "%u\n", dev_to_i3cmaster(dev)->dev_nack_retry);
> +}
> +
> +static ssize_t dev_nack_retry_store(struct device *dev, struct device_attribute *attr,
> +				    const char *buf, size_t count)
> +{
> +	struct i3c_bus *i3cbus = dev_to_i3cbus(dev);
> +	struct i3c_master_controller *master = dev_to_i3cmaster(dev);
> +	unsigned long val;
> +	int ret;
> +
> +	ret = kstrtoul(buf, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	i3c_bus_maintenance_lock(i3cbus);
> +	ret = master->ops->set_dev_nack_retry(master, val);
> +	i3c_bus_maintenance_unlock(i3cbus);
> +
> +	if (ret)
> +		return ret;
> +
> +	master->dev_nack_retry = val;
> +
> +	return count;
> +}
> +
> +static DEVICE_ATTR_RW(dev_nack_retry);

Shouldn't that be dev_nack_retry_count ?

> +
>  static struct attribute *i3c_masterdev_attrs[] = {
>  	&dev_attr_mode.attr,
>  	&dev_attr_current_master.attr,
> @@ -2962,6 +2994,9 @@ int i3c_master_register(struct i3c_master_controller *master,
>  	i3c_master_register_new_i3c_devs(master);
>  	i3c_bus_normaluse_unlock(&master->bus);
>  
> +	if (master->ops->set_dev_nack_retry)
> +		device_create_file(&master->dev, &dev_attr_dev_nack_retry);
> +
>  	return 0;
>  
>  err_del_dev:
> @@ -2987,6 +3022,9 @@ void i3c_master_unregister(struct i3c_master_controller *master)
>  {
>  	i3c_bus_notify(&master->bus, I3C_NOTIFY_BUS_REMOVE);
>  
> +	if (master->ops->set_dev_nack_retry)
> +		device_remove_file(&master->dev, &dev_attr_dev_nack_retry);
> +
>  	i3c_master_i2c_adapter_cleanup(master);
>  	i3c_master_unregister_i3c_devs(master);
>  	i3c_master_bus_cleanup(master);
> diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
> index c52a82dd79a6..5a03e5aea6c2 100644
> --- a/include/linux/i3c/master.h
> +++ b/include/linux/i3c/master.h
> @@ -462,6 +462,8 @@ struct i3c_bus {
>   * @enable_hotjoin: enable hot join event detect.
>   * @disable_hotjoin: disable hot join event detect.
>   * @set_speed: adjust I3C open drain mode timing.
> + * @set_dev_nack_retry: configure device NACK retry count for the master
> + *                      controller.
>   */
>  struct i3c_master_controller_ops {
>  	int (*bus_init)(struct i3c_master_controller *master);
> @@ -491,6 +493,8 @@ struct i3c_master_controller_ops {
>  	int (*enable_hotjoin)(struct i3c_master_controller *master);
>  	int (*disable_hotjoin)(struct i3c_master_controller *master);
>  	int (*set_speed)(struct i3c_master_controller *master, enum i3c_open_drain_speed speed);
> +	int (*set_dev_nack_retry)(struct i3c_master_controller *master,
> +				  unsigned long dev_nack_retry_cnt);
>  };
>  
>  /**
> @@ -510,6 +514,7 @@ struct i3c_master_controller_ops {
>   * @boardinfo: board-level information attached to devices connected on the bus
>   * @bus: I3C bus exposed by this master
>   * @wq: workqueue which can be used by master
> + * @dev_nack_retry: retry count when slave device nack
>   *	drivers if they need to postpone operations that need to take place
>   *	in a thread context. Typical examples are Hot Join processing which
>   *	requires taking the bus lock in maintenance, which in turn, can only
> @@ -534,6 +539,7 @@ struct i3c_master_controller {
>  	} boardinfo;
>  	struct i3c_bus bus;
>  	struct workqueue_struct *wq;
> +	unsigned int dev_nack_retry;
>  };
>  
>  /**
> -- 
> 2.49.GIT
> 

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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