Re: [v4,2/2] i2c: mux: pca954x: support property idle-state

[Peter Rosin <peda@axentia.se>]

On 2019-10-21 10:00, Biwen Li wrote:
> This supports property idle-state
> 

You should expand this a little bit to explain that idle-state, if present,
overrides i2c-mux-idle-disconnect. You could also mention your use case
where you need to avoid disconnects on probe/resume.

> Signed-off-by: Biwen Li <biwen.li@nxp.com>
> ---
> Change in v4:
> 	- rename function
> 	  pca954x_calculate_chan -> pca954x_regval
> 
> Change in v3:
> 	- update subject and description
> 	- add a helper function pca954x_calculate_chan()
> 
> Change in v2:
> 	- update subject and description
> 	- add property idle-state
> 
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 59 ++++++++++++++++++-----------
>  1 file changed, 36 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 923aa3a5a3dc..e566c4cd8ba5 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -86,7 +86,7 @@ struct pca954x {
>  
>  	u8 last_chan;		/* last register value */
>  	/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
> -	s8 idle_state;
> +	s32 idle_state;
>  
>  	struct i2c_client *client;
>  
> @@ -229,20 +229,23 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
>  				I2C_SMBUS_BYTE, &dummy);
>  }
>  
> +static u8 pca954x_regval(struct pca954x *data, u8 chan)
> +{
> +	/* we make switches look like muxes, not sure how to be smarter */

I know you are just moving the comment around, but please fix the sentence
to start with a capital letter and end with a period. Sorry I didn't
catch this in v3.

> +	if (data->chip->muxtype == pca954x_ismux)
> +		return chan | data->chip->enable;
> +	else
> +		return 1 << chan;
> +}
> +
>  static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
>  {
>  	struct pca954x *data = i2c_mux_priv(muxc);
>  	struct i2c_client *client = data->client;
> -	const struct chip_desc *chip = data->chip;
>  	u8 regval;
>  	int ret = 0;
>  
> -	/* we make switches look like muxes, not sure how to be smarter */
> -	if (chip->muxtype == pca954x_ismux)
> -		regval = chan | chip->enable;
> -	else
> -		regval = 1 << chan;
> -
> +	regval = pca954x_regval(data, (u8)(chan & 0xff));

Both a mask and a cast to do what the compiler should be doing all by itself?
If you need to kill a warning, or something, please do just one or them. But
personally I prefer the short, sweet and uncluttered:

	regval = pca954x_regval(data, chan);

>  	/* Only select the channel if its different from the last channel */
>  	if (data->last_chan != regval) {
>  		ret = pca954x_reg_write(muxc->parent, client, regval);
> @@ -256,7 +259,7 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
>  {
>  	struct pca954x *data = i2c_mux_priv(muxc);
>  	struct i2c_client *client = data->client;
> -	s8 idle_state;
> +	s32 idle_state;
>  
>  	idle_state = READ_ONCE(data->idle_state);
>  	if (idle_state >= 0)
> @@ -402,6 +405,17 @@ static void pca954x_cleanup(struct i2c_mux_core *muxc)
>  	i2c_mux_del_adapters(muxc);
>  }
>  
> +static int pca954x_init(struct i2c_client *client, struct pca954x *data)
> +{
> +	if (data->idle_state >= 0) {
> +		data->last_chan = pca954x_regval(data, (u8)(data->idle_state & 0xff));

Dito.

> +	} else {
> +		/* Disconnect multiplexer */
> +		data->last_chan = 0;
> +	}
> +	return i2c_smbus_write_byte(client, data->last_chan);

Here's another thing I missed in the earlier iterations. If i2c_smbus_write_byte
fails here, I think you should set data->last_chan to zero. For the call from
probe it obviously doesn't matter much, but I think the call during resume is
better off with such extra precaution in place.

Cheers,
Peter

> +}
> +
>  /*
>   * I2C init/probing/exit functions
>   */
> @@ -411,7 +425,6 @@ static int pca954x_probe(struct i2c_client *client,
>  	struct i2c_adapter *adap = client->adapter;
>  	struct device *dev = &client->dev;
>  	struct device_node *np = dev->of_node;
> -	bool idle_disconnect_dt;
>  	struct gpio_desc *gpio;
>  	struct i2c_mux_core *muxc;
>  	struct pca954x *data;
> @@ -462,23 +475,24 @@ static int pca954x_probe(struct i2c_client *client,
>  		}
>  	}
>  
> -	/* Write the mux register at addr to verify
> +	data->idle_state = MUX_IDLE_AS_IS;
> +	if (of_property_read_u32(np, "idle-state", &data->idle_state)) {
> +		if (np && of_property_read_bool(np, "i2c-mux-idle-disconnect"))
> +			data->idle_state = MUX_IDLE_DISCONNECT;
> +	}
> +
> +	/*
> +	 * Write the mux register at addr to verify
>  	 * that the mux is in fact present. This also
> -	 * initializes the mux to disconnected state.
> +	 * initializes the mux to a channel
> +	 * or disconnected state.
>  	 */
> -	if (i2c_smbus_write_byte(client, 0) < 0) {
> +	ret = pca954x_init(client, data);
> +	if (ret < 0) {
>  		dev_warn(dev, "probe failed\n");
>  		return -ENODEV;
>  	}
>  
> -	data->last_chan = 0;		   /* force the first selection */
> -	data->idle_state = MUX_IDLE_AS_IS;
> -
> -	idle_disconnect_dt = np &&
> -		of_property_read_bool(np, "i2c-mux-idle-disconnect");
> -	if (idle_disconnect_dt)
> -		data->idle_state = MUX_IDLE_DISCONNECT;
> -
>  	ret = pca954x_irq_setup(muxc);
>  	if (ret)
>  		goto fail_cleanup;
> @@ -531,8 +545,7 @@ static int pca954x_resume(struct device *dev)
>  	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
>  	struct pca954x *data = i2c_mux_priv(muxc);
>  
> -	data->last_chan = 0;
> -	return i2c_smbus_write_byte(client, 0);
> +	return pca954x_init(client, data);
>  }
>  #endif
>  
>