Re: [PATCH] of: i2c: Add DT bindings for idle states to PCA954x mux driver

[Alexander Sverdlin <alexander.sverdlin-OYasijW0DpE@public.gmane.org>]

Hello Laurent,

On 15/12/14 09:40, ext Laurent Pinchart wrote:
>> of: i2c: Add DT bindings for idle states to PCA954x mux driver
>>
>> Introduce two new device tree bindings to specify idle state of PCA954x
>> family of I2C multiplexors:
>>   - idle-state: specifies particular child bus to be selected in idle;
>>   - idle-disconnect: signals that mux should disconnect all child buses in
>> idle;
> 
> Could you please briefly explain your use case(s) for those two properties ?

idle-state specifies which bus will be connected when there is no data transfer.
i2c-mux-gpio also has "idle-state" (though, it can replace both connect and
disconnect cases in my patch). i2c-mux-pinctrl has special "idle" convention,
specifying idle state as last in the list of states. Again, it can serve for
both my properties.

idle-disconnect is what we actually use for some security reasons (so that
I2C bus of the external SFP cage is not connected to the rest of I2C bus
in idle).
 
>> Signed-off-by: Alexander Sverdlin <alexander.sverdlin-OYasijW0DpE@public.gmane.org>
>> ---
>>  .../devicetree/bindings/i2c/i2c-mux-pca954x.txt    |    3 +
>>  drivers/i2c/muxes/i2c-mux-pca954x.c                |   51 +++++++++++++++--
>>  2 files changed, 48 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
>> b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt index
>> 34a3fb6..1fbe287 100644
>> --- a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
>> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
>> @@ -16,6 +16,9 @@ Required Properties:
>>  Optional Properties:
>>
>>    - reset-gpios: Reference to the GPIO connected to the reset input.
>> +  - idle-state: Child bus connected in idle state (specified by its "reg"
>> value) +  - idle-disconnect: Boolean; if defined, forces mux to disconnect
>> all children +    in idle state
>>
>>
>>  Example:
>> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c
>> b/drivers/i2c/muxes/i2c-mux-pca954x.c index ec11b40..69cf603 100644
>> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
>> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
>> @@ -43,6 +43,7 @@
>>  #include <linux/module.h>
>>  #include <linux/pm.h>
>>  #include <linux/slab.h>
>> +#include <linux/of.h>
> 
> Could you please keep headers sorted alphabetically ?

Yes...

>>  #define PCA954X_MAX_NCHANS 8
>>
>> @@ -62,6 +63,8 @@ struct pca954x {
>>  	struct i2c_adapter *virt_adaps[PCA954X_MAX_NCHANS];
>>
>>  	u8 last_chan;		/* last register value */
>> +	bool idle_disconnect;
>> +	s8 idle_chan;		/* valid if not negative */
>>  };
>>
>>  struct chip_desc {
>> @@ -172,10 +175,20 @@ static int pca954x_deselect_mux(struct i2c_adapter
>> *adap, void *client, u32 chan)
>>  {
>>  	struct pca954x *data = i2c_get_clientdata(client);
>> +	struct pca954x_platform_data *pdata =
>> +		dev_get_platdata(&((struct i2c_client *)client)->dev);
>> +
>> +	if ((pdata && pdata->modes[chan].deselect_on_exit) ||
>> +	    data->idle_disconnect) {
> 
> I would copy pdata->modes[chan].deselect_on_exit to data->idle_disconnect in 
> the probe function, so you could avoiding accessing pdata here.

Unfortunately, this pdata has different (per-channel) semantics. I cannot really
understand, why it was done this way, but anyway it's not possible to use one global
bit to represent per-channel bits without changing the behavior.

I'm not keen to brake out-of-tree code (if any), but may be it will be decided to
drop this per-channel deselect_on_exit, because it's not used at least in the 
kernel tree...

>> +		/* Deselect active channel */
>> +		data->last_chan = 0;
>> +		return pca954x_reg_write(adap, client, data->last_chan);
>> +	}
>>
>> -	/* Deselect active channel */
>> -	data->last_chan = 0;
>> -	return pca954x_reg_write(adap, client, data->last_chan);
>> +	if (data->idle_chan >= 0)
>> +		return pca954x_select_chan(adap, client, data->idle_chan);
>> +
>> +	return 0;
>>  }
>>
>>  /*
>> @@ -186,6 +199,7 @@ static int pca954x_probe(struct i2c_client *client,
>>  {
>>  	struct i2c_adapter *adap = to_i2c_adapter(client->dev.parent);
>>  	struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
>> +	struct device_node *of_node = client->dev.of_node;
>>  	struct gpio_desc *gpio;
>>  	int num, force, class;
>>  	struct pca954x *data;
>> @@ -216,6 +230,27 @@ static int pca954x_probe(struct i2c_client *client,
>>
>>  	data->type = id->driver_data;
>>  	data->last_chan = 0;		   /* force the first selection */
>> +	data->idle_chan = -1;		   /* no forced idle state */
>> +
>> +	if (of_node) {
>> +		u32 ch;
>> +
>> +		if (of_property_read_bool(of_node, "idle-disconnect"))
>> +			data->idle_disconnect = true;
>> +
>> +		if (!of_property_read_u32_index(of_node, "idle-state", 0, &ch)) {
>> +			if (ch < PCA954X_MAX_NCHANS) {
>> +				data->idle_chan = ch;
>> +				/* Force idle state from the beginning */
>> +				ret = pca954x_select_chan(adap, client, ch);
>> +				if (ret)
>> +					return ret;
>> +			} else {
>> +				dev_warn(&client->dev,
>> +				         "Invalid idle-state property\n");
>> +			}
>> +		}
>> +	}
>>
>>  	/* Now create an adapter for each channel */
>>  	for (num = 0; num < chips[data->type].nchans; num++) {
>> @@ -234,8 +269,7 @@ static int pca954x_probe(struct i2c_client *client,
>>  		data->virt_adaps[num] =
>>  			i2c_add_mux_adapter(adap, &client->dev, client,
>>  				force, num, class, pca954x_select_chan,
>> -				(pdata && pdata->modes[num].deselect_on_exit)
>> -					? pca954x_deselect_mux : NULL);
>> +				pca954x_deselect_mux);
>>
>>  		if (data->virt_adaps[num] == NULL) {
>>  			ret = -ENODEV;
>> @@ -281,7 +315,12 @@ static int pca954x_resume(struct device *dev)
>>  	struct pca954x *data = i2c_get_clientdata(client);
>>
>>  	data->last_chan = 0;
>> -	return i2c_smbus_write_byte(client, 0);
>> +	/* Restore idle state on resume */
>> +	if (data->idle_chan >= 0)
>> +		return pca954x_select_chan(to_i2c_adapter(client->dev.parent),
>> +		                           client, data->idle_chan);
>> +	else
>> +		return i2c_smbus_write_byte(client, 0);
>>  }
>>  #endif
> 

-- 
Best regards,
Alexander Sverdlin.