Date:   Mon, 29 Nov 2021 15:01:31 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Peter Rosin <peda@...ntia.se>
CC:     Vignesh Raghavendra <vigneshr@...com>, Nishanth Menon <nm@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-can@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH RFC v3 1/4] dt-bindings: mux: Increase the number of
 arguments in mux-controls

Hi Peter,

On 29/11/21 1:45 pm, Peter Rosin wrote:
> 
> 
> 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.
> 

Sorry, but how is this different from the case of

#mux-control-cells = 1

If #mux-control-cells is equal to 1 it means the consumer will use a
given control line from the mux chip. The same would be the case when we
will be using, #mux-control-cells is equal to 2, except we can also
provide the state.

If the consumer will use all the lines then #mux-control-cells will be
set to 0. In this condition the state can't be provided from the DT and
the consumer will be controlling the entire mux chip. If
#mux-control-cells is greater than 0 then we will not be able to provide
multiple lines of control using a single mux-controls entry(mux-controls
= <...>;) right? We would have the using multiple mux-controls
entries(mux-controls = <...>, <...>;).

Thanks,
Aswath

> 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@...com>
>>>> ---
>>>>  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
>>>>
>>
> 

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