Re: [PATCH RFC v3 1/4] dt-bindings: mux: Increase the number of arguments in mux-controls

[Peter Rosin]

On 2021-11-29 05:36, Aswath Govindraju wrote:
> Hi Peter,
> 
> On 25/11/21 7:05 pm, Peter Rosin wrote:
>> Hi!
>>
>> You need to have some description on how #mux-control-cells now work.
>> The previous description is in mux-consumer.yaml and an update there
>> is needed.
>>
>> However, I have realized that the adg792a binding uses #mux-control-cells
>> to indicate if it should expose its three muxes with one mux-control
>> and operate the muxes in parallel, or if it should be expose three
>> independent mux-controls. So, the approach in this series to always
>> have the #mux-control-cells property fixed at <2> when indicating a
>> state will not work for that binding. And I see no fix for that binding
>> without adding a new property.
>>
>> So, I would like a different approach. Since I dislike how mux-controls
>> -after this series- is not (always) specifying a mux-control like the name
>> says, but instead optionally a specific state, the new property I would
>> like to add is #mux-state-cells such that it would always be one more
>> than #mux-control-cells.
>>
>> 	mux: mux-controller {
>> 		compatible = "gpio-mux";
>> 		#mux-control-cells = <0>;
>> 		#mux-state-cells = <1>;
>>
>> 		mux-gpios = <...>;
>> 	};
>>
>> 	can-phy {
>> 		compatible = "ti,tcan1043";
>> 		...
>> 		mux-states = <&mux 1>;
>> 	};
>>
>> That solves the naming issue, the unused argument for mux-conrtrollers
>> that previously had #mux-control-cells = <0>, and the binding for adg792a
>> need no longer be inconsistent.
>>
>> Or, how should this be solved? I'm sure there are other options...
>>
> 
> 
> I feel that the new approach using mux-state-cells seems to be
> overpopulating the device tree nodes, when the state can be represented
> using the control cells. I understand that the definition for
> mux-controls is to only specify the control line to be used in a given
> mux. Can't it now be upgraded to also represent the state at which the
> control line has to be set to?
> 
> With respect to adg792a, it is inline with the current implementation
> and the only change I think would be required in the driver is,

No, that does not work. See below.

> 
> diff --git a/drivers/mux/adg792a.c b/drivers/mux/adg792a.c
> index e8fc2fc1ab09..2cd3bb8a40d4 100644
> --- a/drivers/mux/adg792a.c
> +++ b/drivers/mux/adg792a.c
> @@ -73,8 +73,6 @@ static int adg792a_probe(struct i2c_client *i2c)
>         ret = device_property_read_u32(dev, "#mux-control-cells", &cells);
>         if (ret < 0)
>                 return ret;
> -       if (cells >= 2)
> -               return -EINVAL;
> 
>         mux_chip = devm_mux_chip_alloc(dev, cells ? 3 : 1, 0);

When you add cell #2 with the state, the cells variable will end up
as 2 always. Which means that there is no way to alloc one mux
control since "cells ? 3 : 1" will always end up as "3", with no
easy fix.

So, your approach does not work for this driver.

Cheers,
Peter

>         if (IS_ERR(mux_chip))
> 
> And the following series should be compatible with it. If adg792a driver
> is the only issue then would there be any issue with only changing it
> and using this implementation?
> 
> Thanks,
> Aswath
> 
> 
> 
> 
>> Cheers,
>> Peter
>>
>> On 2021-11-23 09:12, Aswath Govindraju wrote:
>>> Increase the allowed number of arguments in mux-controls to add support for
>>> passing information regarding the state of the mux to be set, for a given
>>> device.
>>>
>>> Signed-off-by: Aswath Govindraju <a-govindraju@xxxxxx>
>>> ---
>>>  Documentation/devicetree/bindings/mux/gpio-mux.yaml       | 2 +-
>>>  Documentation/devicetree/bindings/mux/mux-controller.yaml | 2 +-
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/mux/gpio-mux.yaml b/Documentation/devicetree/bindings/mux/gpio-mux.yaml
>>> index 0a7c8d64981a..c810b7df39de 100644
>>> --- a/Documentation/devicetree/bindings/mux/gpio-mux.yaml
>>> +++ b/Documentation/devicetree/bindings/mux/gpio-mux.yaml
>>> @@ -26,7 +26,7 @@ properties:
>>>        List of gpios used to control the multiplexer, least significant bit first.
>>>  
>>>    '#mux-control-cells':
>>> -    const: 0
>>> +    enum: [ 0, 1, 2 ]
>>>  
>>>    idle-state:
>>>      default: -1
>>> diff --git a/Documentation/devicetree/bindings/mux/mux-controller.yaml b/Documentation/devicetree/bindings/mux/mux-controller.yaml
>>> index 736a84c3b6a5..0b4b067a97bf 100644
>>> --- a/Documentation/devicetree/bindings/mux/mux-controller.yaml
>>> +++ b/Documentation/devicetree/bindings/mux/mux-controller.yaml
>>> @@ -73,7 +73,7 @@ properties:
>>>      pattern: '^mux-controller(@.*|-[0-9a-f]+)?$'
>>>  
>>>    '#mux-control-cells':
>>> -    enum: [ 0, 1 ]
>>> +    enum: [ 0, 1, 2 ]
>>>  
>>>    idle-state:
>>>      $ref: /schemas/types.yaml#/definitions/int32
>>>
>