Hello Laurent,
On 16/12/14 12:07, 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).
>
> Thank you for the explanation. I would add it to the DT bindings
> documentation, or at least to the commit message.
Ok, I'll send v2 with all your comments addressed.
> I understand the use cases of the idle-disconnect property. What do you use
> idle-state for, when the idle state is different from disconnecting the bus ?
We do not have a use case for that. It was done only for the sake of completeness.
Because other MUXes actually offer user this possibility. I was initially thinking
about providing this on i2c-mux level for all of them, but unfortunately they all
use deselect callback in different way and pinctrl is the worst case, as idle
state cannot be represented with an int, but should be a pointer.
Anyway, if you think there is no use-case for this, I can drop this part.
>>>> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxx>
>>>> ---
>>>>
>>>> .../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...
>
> I'd vote for removing deselect_on_exit from platform data, but I won't insist.
Then it should be a separate patch, probably... I can send a series removing pdata
pits and adding a DT binding.
>>>> + /* 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.
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