Re: [PATCH v2 1/2] dt-bindings: net: bluetooth: Add MediaTek MT7921S SDIO Bluetooth

[Chen-Yu Tsai]

(+CC Ulf Hansson)

On Wed, Jan 31, 2024 at 6:38 AM Rob Herring <robh@xxxxxxxxxx> wrote:
>
> On Tue, Jan 30, 2024 at 05:25:38PM +0100, Krzysztof Kozlowski wrote:
> > On 30/01/2024 08:47, Chen-Yu Tsai wrote:
> > > On Tue, Jan 30, 2024 at 3:37 PM Krzysztof Kozlowski
> > > <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> > >>
> > >> On 30/01/2024 04:32, Chen-Yu Tsai wrote:
> > >>> On Mon, Jan 29, 2024 at 3:34 PM Krzysztof Kozlowski
> > >>> <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> > >>>>
> > >>>> On 29/01/2024 04:38, Chen-Yu Tsai wrote:
> > >>>>
> > >>>>>>> +allOf:
> > >>>>>>> +  - $ref: bluetooth-controller.yaml#
> > >>>>>>> +
> > >>>>>>> +properties:
> > >>>>>>> +  compatible:
> > >>>>>>> +    enum:
> > >>>>>>> +      - mediatek,mt7921s-bluetooth
> > >>>>>>
> > >>>>>> Can it be also WiFi on separate bus? How many device nodes do you need
> > >>>>>> for this device?
> > >>>>>
> > >>>>> For the "S" variant, WiFi is also on SDIO. For the other two variants,
> > >>>>> "U" and "E", WiFi goes over USB and PCIe respectively. On both those
> > >>>>> variants, Bluetooth can either go over USB or UART. That is what I
> > >>>>> gathered from the pinouts. There are a dozen GPIO pins which don't
> > >>>>> have detailed descriptions though. If you want a comprehensive
> > >>>>> binding of the whole chip and all its variants, I suggest we ask
> > >>>>> MediaTek to provide it instead. My goal with the binding is to document
> > >>>>> existing usage and allow me to upstream new device trees.
> > >>>>>
> > >>>>> For now we only need the Bluetooth node. The WiFi part is perfectly
> > >>>>> detectable, and the driver doesn't seem to need the WiFi reset pin.
> > >>>>> The Bluetooth driver only uses its reset pin to reset a hung controller.
> > >>>>
> > >>>> Then suffix "bluetooth" seems redundant.
> > >>>
> > >>> I think keeping the suffix makes more sense though. The chip is a two
> > >>> function piece, and this only targets one of the functions. Also, the
> > >>
> > >> That's why I asked and you said there is only one interface: SDIO.
> > >
> > > There's only one interface, SDIO, but two SDIO functions. The two
> > > functions, if both were to be described in the device tree, would
> > > be two separate nodes. We just don't have any use for the WiFi one
> > > right now. Does that make sense to keep the suffix?
> >
> > Number of functions does not really matter. Number of interfaces on the
> > bus would matter. Why would you have two separate nodes for the same
> > SDIO interface? Or do you want to say there are two interfaces?

There is only one external interface. I don't know how the functions
are stitched together internally.

It could be that the separate functions have nothing in common other
than sharing a standard external SDIO interface. Each function can be
individually controlled, and operations for different functions are
directed internally to the corresponding core.

> Right, one device at 2 addresses on a bus should be a node with 2 "reg"
> entries, not 2 nodes with 1 "reg" address each.

AFAICU that's not what the MMC controller binding, which I quote below,
says. It implies that each SDIO function shall be a separate node under
the MMC controller node.


patternProperties:
  "^.*@[0-9]+$":
    type: object
    description: |
      On embedded systems the cards connected to a host may need
      additional properties. These can be specified in subnodes to the
      host controller node. The subnodes are identified by the
      standard \'reg\' property. Which information exactly can be
      specified depends on the bindings for the SDIO function driver
      for the subnode, as specified by the compatible string.

    properties:
      compatible:
        description: |
          Name of SDIO function following generic names recommended
          practice

      reg:
        items:
          - minimum: 0
            maximum: 7
            description:
              Must contain the SDIO function number of the function this
              subnode describes. A value of 0 denotes the memory SD
              function, values from 1 to 7 denote the SDIO functions.


ChenYu