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

[Krzysztof Kozlowski <krzk@kernel.org>]

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@suse.de>.
>>
>> Co-developed-by: Andreas Färber <afaerber@suse.de>
>> Signed-off-by: Andreas Färber <afaerber@suse.de>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>> 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@suse.de>
>> +  - Heiner Kallweit <hkallweit1@gmail.com>
>> +
>> +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.

Best regards,
Best regards,
Krzysztof