Re: [PATCH v3 09/11] dt-bindings: input: Document hid-over-spi DT schema

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Thu, Apr 09, 2026 at 05:02:11PM +0100, Conor Dooley wrote:
> On Thu, Apr 02, 2026 at 01:59:46AM +0000, Jingyuan Liang wrote:
> > Documentation describes the required and optional properties for
> > implementing Device Tree for a Microsoft G6 Touch Digitizer that
> > supports HID over SPI Protocol 1.0 specification.
> > 
> > The properties are common to HID over SPI.
> > 
> > Signed-off-by: Dmitry Antipov <dmanti@microsoft.com>
> > Signed-off-by: Jarrett Schultz <jaschultz@microsoft.com>
> > Signed-off-by: Jingyuan Liang <jingyliang@chromium.org>
> > ---
> >  .../devicetree/bindings/input/hid-over-spi.yaml    | 126 +++++++++++++++++++++
> >  1 file changed, 126 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/input/hid-over-spi.yaml b/Documentation/devicetree/bindings/input/hid-over-spi.yaml
> > new file mode 100644
> > index 000000000000..d1b0a2e26c32
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/input/hid-over-spi.yaml
> > @@ -0,0 +1,126 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/input/hid-over-spi.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: HID over SPI Devices
> > +
> > +maintainers:
> > +  - Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > +  - Jiri Kosina <jkosina@suse.cz>
> 
> Why them and not you, the developers of the series?
> 
> > +
> > +description: |+
> > +  HID over SPI provides support for various Human Interface Devices over the
> > +  SPI bus. These devices can be for example touchpads, keyboards, touch screens
> > +  or sensors.
> > +
> > +  The specification has been written by Microsoft and is currently available
> > +  here: https://www.microsoft.com/en-us/download/details.aspx?id=103325
> > +
> > +  If this binding is used, the kernel module spi-hid will handle the
> > +  communication with the device and the generic hid core layer will handle the
> > +  protocol.
> 
> This is not relevant to the binding, please remove it.
> 
> > +
> > +allOf:
> > +  - $ref: /schemas/input/touchscreen/touchscreen.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    oneOf:
> > +      - items:
> > +          - enum:
> > +              - microsoft,g6-touch-digitizer
> > +          - const: hid-over-spi
> > +      - description: Just "hid-over-spi" alone is allowed, but not recommended.
> > +        const: hid-over-spi
> 
> Why is it allowed but not recommended? Seems to me like we should
> require device-specific compatibles.

Why would we want to change the driver code to add a new compatible each
time a vendor decides to create a chip that is fully hid-spi-protocol
compliant? Or is the plan to still allow "hid-over-spi" fallback but
require device-specific compatible that will be ignored unless there is
device-specific quirk needed?

> 
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> > +    description:
> > +      GPIO specifier for the digitizer's reset pin (active low). The line must
> > +      be flagged with GPIO_ACTIVE_LOW.
> > +
> > +  vdd-supply:
> > +    description:
> > +      Regulator for the VDD supply voltage.
> > +
> > +  input-report-header-address:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    minimum: 0
> > +    maximum: 0xffffff
> > +    description:
> > +      A value to be included in the Read Approval packet, listing an address of
> > +      the input report header to be put on the SPI bus. This address has 24
> > +      bits.
> > +
> > +  input-report-body-address:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    minimum: 0
> > +    maximum: 0xffffff
> > +    description:
> > +      A value to be included in the Read Approval packet, listing an address of
> > +      the input report body to be put on the SPI bus. This address has 24 bits.
> > +
> > +  output-report-address:
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    minimum: 0
> > +    maximum: 0xffffff
> > +    description:
> > +      A value to be included in the Output Report sent by the host, listing an
> > +      address where the output report on the SPI bus is to be written to. This
> > +      address has 24 bits.
> > +
> > +  read-opcode:
> > +    $ref: /schemas/types.yaml#/definitions/uint8
> > +    description:
> > +      Value to be used in Read Approval packets. 1 byte.
> > +
> > +  write-opcode:
> > +    $ref: /schemas/types.yaml#/definitions/uint8
> > +    description:
> > +      Value to be used in Write Approval packets. 1 byte.
> 
> Why can none of these things be determined from the device's compatible?
> On the surface, they like the kinds of things that could/should be.

Why would we want to keep tables of these values in the kernel and again
have to update the driver for each new chip? It also probably
firmware-dependent.

Thanks.

-- 
Dmitry