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

On 18/03/2022 21:50, Robin Murphy wrote:

On 2022-02-25 21:13, Heiner Kallweit wrote:

quoted

Add a YAML schema binding for TM1628 auxdisplay
(7/11-segment LED) controller.

This patch is partially based on previous work from
Andreas Färber [off-list ref].

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.

quoted

+
+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

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