linux-kernel - Re: [v2,2/2] i2c: mux: pca954x: add property idle-state

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Date:   Tue, 15 Oct 2019 13:59:54 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Biwen Li <biwen.li@....com>,
        "leoyang.li@....com" <leoyang.li@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>
CC:     "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [v2,2/2] i2c: mux: pca954x: add property idle-state

On 2019-10-15 06:48, Biwen Li wrote:
> This adds property idle-state
> 
> Signed-off-by: Biwen Li <biwen.li@....com>
> ---
> Change in v2:
> 	- update subject and description
> 	- add property idle-state
> 
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 47 ++++++++++++++++++-----------
>  1 file changed, 30 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 923aa3a5a3dc..8ec586342b92 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;
>  
> @@ -256,7 +256,7 @@ 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 +402,25 @@ 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)
> +{
> +	/*
> +	 * Write the mux register at addr to verify
> +	 * that the mux is in fact present. This also
> +	 * initializes the mux to disconnected state.
> +	 */

This comment belongs in pca954x_probe, before the call to this function.
However, the comment may now be be wrong since the mux is not always
initialized to the disconnected state.

> +	if (data->idle_state >= 0) {
> +		/* Always enable multiplexer */

While I understand that it is important for your case that the mux is
always enabled, this is just a side effect of having a specific
idle-state. I suggest that you remove this comment.

> +		if (data->chip->muxtype == pca954x_ismux)
> +			data->last_chan = data->idle_state | data->chip->enable;
> +		else
> +			data->last_chan = 1 << data->idle_state;

The meat of this "if" is still duplicated, I was suggesting a helper
that only did the regval calculation so that the new helper could
also be used from pca954x_select_chan.

> +	} else {
> +		/* Disconnect multiplexer */
> +		data->last_chan = 0; /* force the first selection */

These two comments should be combined.

> +	}
> +	return i2c_smbus_write_byte(client, data->last_chan);
> +}
>  /*
>   * I2C init/probing/exit functions
>   */
> @@ -411,7 +430,6 @@ 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;
> @@ -462,22 +480,18 @@ static int pca954x_probe(struct i2c_client *client,
>  		}
>  	}
>  
> -	/* Write the mux register at addr to verify
> -	 * that the mux is in fact present. This also
> -	 * initializes the mux to disconnected state.
> -	 */
> -	if (i2c_smbus_write_byte(client, 0) < 0) {
> +	if (of_property_read_u32(np, "idle-state", &data->idle_state))
> +		data->idle_state = MUX_IDLE_AS_IS;
> +
> +	if (of_property_read_bool(np, "i2c-mux-idle-disconnect"))
> +		data->idle_state = MUX_IDLE_DISCONNECT;

I think you should ignore i2c-mux-idle-disconnect if idle-state is present.
I.e. move this "if" statement into the body of the former "if". Also, you have
broken things if np is NULL.

Cheers,
Peter

> +
> +	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)
> @@ -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
>  
>