Re: [PATCH v5 2/6] dt-bindings: auxdisplay: Add Titan Micro Electronics TM1628

[Heiner Kallweit <hkallweit1@xxxxxxxxx>]

On 23.03.2022 21:33, Heiner Kallweit wrote:
> On 21.03.2022 09:34, Krzysztof Kozlowski wrote:
>> On 18/03/2022 21:50, Robin Murphy wrote:
>>> On 2022-02-25 21:13, Heiner Kallweit wrote:
>>>> Add a YAML schema binding for TM1628 auxdisplay
>>>> (7/11-segment LED) controller.
>>>>
>>>> This patch is partially based on previous work from
>>>> Andreas Färber <afaerber@xxxxxxx>.
>>>>
>>>> Co-developed-by: Andreas Färber <afaerber@xxxxxxx>
>>>> Signed-off-by: Andreas Färber <afaerber@xxxxxxx>
>>>> Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
>>>> ---
>>>> v5:
>>>> - add vendor prefix to driver-specific properties
>>>> ---
>>>>   .../bindings/auxdisplay/titanmec,tm1628.yaml  | 92 +++++++++++++++++++
>>>>   1 file changed, 92 insertions(+)
>>>>   create mode 100644 Documentation/devicetree/bindings/auxdisplay/titanmec,tm1628.yaml
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/auxdisplay/titanmec,tm1628.yaml b/Documentation/devicetree/bindings/auxdisplay/titanmec,tm1628.yaml
>>>> new file mode 100644
>>>> index 000000000..2a1ef692c
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/auxdisplay/titanmec,tm1628.yaml
>>>> @@ -0,0 +1,92 @@
>>>> +# SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/auxdisplay/titanmec,tm1628.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: Titan Micro Electronics TM1628 LED controller
>>>> +
>>>> +maintainers:
>>>> +  - Andreas Färber <afaerber@xxxxxxx>
>>>> +  - Heiner Kallweit <hkallweit1@xxxxxxxxx>
>>>> +
>>>> +allOf:
>>>> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    const: titanmec,tm1628
>>>> +
>>>> +  reg:
>>>> +    maxItems: 1
>>>> +
>>>> +  titanmec,grid:
>>>> +    description:
>>>> +      Mapping of display digit position to grid number.
>>>> +      This implicitly defines the display size.
>>>> +    $ref: /schemas/types.yaml#/definitions/uint8-array
>>>> +    minItems: 1
>>>> +    maxItems: 7
>>>> +
>>>> +  titanmec,segment-mapping:
>>>> +    description:
>>>> +      Mapping of 7 segment display segments A-G to bit numbers 1-12.
>>>> +    $ref: /schemas/types.yaml#/definitions/uint8-array
>>>> +    minItems: 7
>>>> +    maxItems: 7
>>>> +
>>>> +  "#address-cells":
>>>> +    const: 2
>>>> +
>>>> +  "#size-cells":
>>>> +    const: 0
>>>> +
>>>> +required:
>>>> +  - compatible
>>>> +  - reg
>>>
>>> Would it be fair to say that "spi-lsb-first" and "spi-3wire" are also 
>>> required? The chips aren't configurable so won't exactly be usable any 
>>> other way. Furthermore I believe the transmission format actually works 
>>> out equivalent to SPI mode 3, so should warrant "spi-cpha" and 
>>> "spi-cpol" as well.
>>>
>>>> +
>>>> +patternProperties:
>>>> +  "^.*@[1-7],([1-9]|1[0-6])$":
>>>> +    type: object
>>>> +    $ref: /schemas/leds/common.yaml#
>>>> +    unevaluatedProperties: false
>>>> +    description: |
>>>> +      Properties for a single LED.
>>>> +
>>>> +    properties:
>>>> +      reg:
>>>> +        description: |
>>>> +          1-based grid number, followed by 1-based segment bit number.
>>>> +        maxItems: 1
>>>> +
>>>> +    required:
>>>> +      - reg
>>>
>>> I'm concerned that this leaves us no room to support the additional 
>>> keypad functionality in future. Having now double-checked a datasheet, 
>>> the inputs are also a two-dimensional mux (sharing the segment lines), 
>>> so the device effectively has two distinct but numerically-overlapping 
>>> child address spaces - one addressed by (grid,segment) and the other by 
>>> (segment,key).
>>>
>>> Rob, Krysztof, any thoughts on the best DT idiom to leave accommodation 
>>> for that? I'm thinking either require an intermediate node to contain 
>>> each notional address space, or perhaps add another leading address cell 
>>> to select between them? I don't believe any of these things have further 
>>> functionality beyond that.
>>
>> I think intermediate nodes - leds, keys - are more appropriate, because
>> it is self-describing. Additional address space number would require
>> decoding this "0" or "1" into LED/key. For complex devices - like PMICs
>> with regulators, RTC and clocks - we already have such patterns.
>>
> Then it's just the question who can implement such an intermediate node
> based on what has been done so far.
> 
As it is now it seems we end up with empty hands again and have to wait
further two years for the next one to make an attempt.
That's a pity because for most users the relevant use cases are supported.

>> Best regards,
>> Best regards,
>> Krzysztof
>