Subject: Re: [PATCH v2 1/2] i2c: smbus: add core function handling SMBus host-notify

From: Wolfram Sang <[email-masked]>
Date: Sat, 25 Jul 2020 22:27:33 +0200

Hi Alain,

some more comments for this one. I hope to come to a conclusion with Rob
regarding the binding for patch 2, so we are then ready to go.

On Fri, Jul 03, 2020 at 01:36:07PM +0200, Alain Volmat wrote:
> SMBus Host-Notify protocol, from the adapter point of view
> consist of receiving a message from a client, including the
> client address and some other data.
> 
> It can be simply handled by creating a new slave device
> and registering a callback performing the parsing of the
> message received from the client.
> 
> This commit introduces two new core functions
>   * i2c_new_slave_host_notify_device
>   * i2c_free_slave_host_notify_device
> that take care of registration of the new slave device and
> callback and will call i2c_handle_smbus_host_notify once a
> Host-Notify event is received.
> 
> Signed-off-by: Alain Volmat <[email-masked]>
> ---
>  v2: identical to v1
> 
>  drivers/i2c/i2c-core-smbus.c | 114 +++++++++++++++++++++++++++++++++++++++++++

I came to the conclusion that this code should be in i2c-smbus.c.
Because it is SMBus only. I agree that the current code layout is
confusing. I will try to move the whole host-notify support to i2c-smbus
in the next cycle.

Yes, that means that one needs to select I2C_SMBUS in the config, too
(unless you want to 'select' it with your driver). But most people won't
need it so they can compile it away. This is what I2C_SMBUS is for.

>  include/linux/i2c-smbus.h    |  12 +++++
>  2 files changed, 126 insertions(+)
> 
> diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> index f5c9787992e9..23ab9dc5ac85 100644
> --- a/drivers/i2c/i2c-core-smbus.c
> +++ b/drivers/i2c/i2c-core-smbus.c
> @@ -715,3 +715,117 @@ int of_i2c_setup_smbus_alert(struct i2c_adapter *adapter)
>  }
>  EXPORT_SYMBOL_GPL(of_i2c_setup_smbus_alert);
>  #endif
> +
> +#if IS_ENABLED(CONFIG_I2C_SLAVE)
> +#define SMBUS_HOST_NOTIFY_LEN	3
> +struct i2c_slave_host_notify_status {
> +	u8 index;
> +	u8 addr;
> +};
> +
> +static int i2c_slave_host_notify_cb(struct i2c_client *client,
> +				    enum i2c_slave_event event, u8 *val)
> +{
> +	struct i2c_slave_host_notify_status *status = client->dev.platform_data;
> +	int ret;
> +

Can't we simplify 'index' handling similar to the testunit driver...

> +	switch (event) {
> +	case I2C_SLAVE_WRITE_REQUESTED:
> +		status->index = 0;

... by removing this line...

> +		break;
> +	case I2C_SLAVE_WRITE_RECEIVED:
> +		/* We only retrieve the first byte received (addr)
> +		 * since there is currently no support to retrieve the data
> +		 * parameter from the client.
> +		 */
> +		if (status->index == 0)
> +			status->addr = *val;
> +		if (status->index < U8_MAX)
> +			status->index++;
> +		break;
> +	case I2C_SLAVE_STOP:
> +		/* Handle host-notify if whole message received only */
> +		if (status->index != SMBUS_HOST_NOTIFY_LEN) {
> +			status->index = U8_MAX;
> +			break;
> +		}
> +
> +		ret = i2c_handle_smbus_host_notify(client->adapter,
> +						   status->addr);
> +		if (ret < 0)
> +			return ret;
> +		status->index = U8_MAX;

... and handling the logic here like:

+		if (status->index == SMBUS_HOST_NOTIFY_LEN)
+			i2c_handle_smbus_host_notify(client->adapter, status->addr);
+		status->index = 0;

Note that I2C_SLAVE_STOP doesn't return a retval, so we don't need to check
i2c_handle_smbus_host_notify().

> +		break;
> +	case I2C_SLAVE_READ_REQUESTED:
> +	case I2C_SLAVE_READ_PROCESSED:
> +		*val = 0xff;
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * i2c_new_slave_host_notify_device - get a client for SMBus host-notify support
> + * @adapter: the target adapter
> + * Context: can sleep
> + *
> + * Setup handling of the SMBus host-notify protocol on a given I2C bus segment.
> + *
> + * Handling is done by creating a device and its callback and handling data
> + * received via the SMBus host-notify address (0x8)
> + *
> + * This returns the client, which should be ultimately freed using
> + * i2c_free_slave_host_notify_device(); or an ERRPTR to indicate an error.
> + */
> +struct i2c_client *i2c_new_slave_host_notify_device(struct i2c_adapter *adapter)
> +{
> +	struct i2c_board_info host_notify_board_info = {
> +		I2C_BOARD_INFO("smbus_host_notify", 0x08),
> +		.flags  = I2C_CLIENT_SLAVE,
> +	};
> +	struct i2c_slave_host_notify_status *status;
> +	struct i2c_client *client;
> +	int ret;
> +
> +	status = kzalloc(sizeof(struct i2c_slave_host_notify_status),
> +			 GFP_KERNEL);
> +	if (!status)
> +		return ERR_PTR(-ENOMEM);
> +	status->index = U8_MAX;

This line could go, too, if my simplification above works.

> +
> +	host_notify_board_info.platform_data = status;
> +
> +	client = i2c_new_client_device(adapter, &host_notify_board_info);
> +	if (IS_ERR(client)) {
> +		kfree(status);
> +		return client;
> +	}
> +
> +	ret = i2c_slave_register(client, i2c_slave_host_notify_cb);
> +	if (ret) {
> +		i2c_unregister_device(client);
> +		kfree(status);
> +		return ERR_PTR(ret);
> +	}
> +
> +	return client;
> +}
> +EXPORT_SYMBOL_GPL(i2c_new_slave_host_notify_device);
> +
> +/**
> + * i2c_free_slave_host_notify_device - free the client for SMBus host-notify
> + * support
> + * @client: the client to free
> + * Context: can sleep
> + *
> + * Free the i2c_client allocated via i2c_new_slave_host_notify_device
> + */
> +void i2c_free_slave_host_notify_device(struct i2c_client *client)
> +{
> +	i2c_slave_unregister(client);
> +	kfree(client->dev.platform_data);
> +	i2c_unregister_device(client);
> +}
> +EXPORT_SYMBOL_GPL(i2c_free_slave_host_notify_device);

Sidenote: With my recent series "i2c: slave: improve sanity checks when
un-/registering" this code became NULL-safe (and IS_ERR safe, too).

> +#endif
> diff --git a/include/linux/i2c-smbus.h b/include/linux/i2c-smbus.h
> index 1e4e0de4ef8b..52e62f398f1c 100644
> --- a/include/linux/i2c-smbus.h
> +++ b/include/linux/i2c-smbus.h
> @@ -38,6 +38,18 @@ static inline int of_i2c_setup_smbus_alert(struct i2c_adapter *adap)
>  	return 0;
>  }
>  #endif
> +#if IS_ENABLED(CONFIG_I2C_SLAVE)
> +struct i2c_client *i2c_new_slave_host_notify_device(struct i2c_adapter *adapter);
> +void i2c_free_slave_host_notify_device(struct i2c_client *client);
> +#else
> +static inline struct i2c_client *i2c_new_slave_host_notify_device(struct i2c_adapter *adapter)
> +{
> +	return NULL;

return ERR_PTR(-ENOSYS);

As the docs say, this function either returns a valid client or an
ERR_PTR.

> +}
> +static inline void i2c_free_slave_host_notify_device(struct i2c_client *client)
> +{
> +}
> +#endif
>  
>  #if IS_ENABLED(CONFIG_I2C_SMBUS) && IS_ENABLED(CONFIG_DMI)
>  void i2c_register_spd(struct i2c_adapter *adap);
> -- 
> 2.7.4
> 
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