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

The MediaTek MT7921S is a WiFi/Bluetooth combo chip that works over
SDIO. While the Bluetooth function is fully discoverable, the chip
has a pin that can reset just the Bluetooth side, as opposed to the
full chip. This needs to be described in the device tree.

Add a device tree binding for MT7921S Bluetooth over SDIO specifically
ot document the reset line.

Cc: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
Changes since v1:
- Reworded descriptions
- Moved binding maintainer section before description
- Added missing reference to bluetooth-controller.yaml
- Added missing GPIO header to example

 .../bluetooth/mediatek,mt7921s-bluetooth.yaml | 53 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 2 files changed, 54 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/net/bluetooth/mediatek,mt7921s-bluetooth.yaml

On Fri, Jan 26, 2024 at 6:40 PM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 26/01/2024 07:34, Chen-Yu Tsai wrote:
> > The MediaTek MT7921S is a WiFi/Bluetooth combo chip that works over
> > SDIO. While the Bluetooth function is fully discoverable, the chip
> > has a pin that can reset just the Bluetooth side, as opposed to the
> > full chip. This needs to be described in the device tree.
> >
> > Add a device tree binding for MT7921S Bluetooth over SDIO specifically
> > ot document the reset line.
>
> s/ot/to/
>
> >
> > Cc: Sean Wang <sean.wang@mediatek.com>
> > Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> > ---
> > Changes since v1:
> > - Reworded descriptions
> > - Moved binding maintainer section before description
> > - Added missing reference to bluetooth-controller.yaml
> > - Added missing GPIO header to example
> >
> >  .../bluetooth/mediatek,mt7921s-bluetooth.yaml | 53 +++++++++++++++++++
> >  MAINTAINERS                                   |  1 +
> >  2 files changed, 54 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/net/bluetooth/mediatek,mt7921s-bluetooth.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/net/bluetooth/mediatek,mt7921s-bluetooth.yaml b/Documentation/devicetree/bindings/net/bluetooth/mediatek,mt7921s-bluetooth.yaml
> > new file mode 100644
> > index 000000000000..ff11c95c816c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/bluetooth/mediatek,mt7921s-bluetooth.yaml
> > @@ -0,0 +1,53 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/net/bluetooth/mediatek,mt7921s-bluetooth.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: MediaTek MT7921S Bluetooth
> > +
> > +maintainers:
> > +  - Sean Wang <sean.wang@mediatek.com>
> > +
> > +description:
> > +  MT7921S is an SDIO-attached dual-radio WiFi+Bluetooth Combo chip; each
> > +  function is its own SDIO function on a shared SDIO interface. The chip
> > +  has two dedicated reset lines, one for each function core.
> > +  This binding only covers the Bluetooth part of the chip.
> > +
> > +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.

> Missing blank line.

Will fix.

> > +  reg:
> > +    const: 2
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> > +    description:
> > +      An active-low reset line for the Bluetooth core; on typical M.2
> > +      key E modules this is the W_DISABLE2# pin.
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +
> > +additionalProperties: false
>
> Instead 'unevaluatedProperties: false'

Will fix.


Thanks
ChenYu

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.



Best regards,
Krzysztof

On Mon, Jan 29, 2024 at 3:34 PM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> 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
compatible string is already used in an existing driver [1] and
soon-to-be in-tree device tree [2].


ChenYu

[1] https://elixir.bootlin.com/linux/latest/source/drivers/bluetooth/btmtksdio.c#L1414
[2] https://elixir.bootlin.com/linux/v6.8-rc1/source/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi-pico6.dts#L86

On Tue, Jan 30, 2024 at 3:37 PM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 30/01/2024 04:32, Chen-Yu Tsai wrote:
> > On Mon, Jan 29, 2024 at 3:34 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski@linaro.org> 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?

> > compatible string is already used in an existing driver [1] and
> > soon-to-be in-tree device tree [2].
>
> That's not the way to upstream compatible. You cannot send it bypassing
> bindings and review and later claim that's an ABI.

I get that. I can fix up the existing users where necessary. A proper
binding would make the driver lookup be more efficient as well.


Thanks
ChenYu

On 30/01/2024 08:47, Chen-Yu Tsai wrote:
> On Tue, Jan 30, 2024 at 3:37 PM Krzysztof Kozlowski
> <krzysztof.kozlowski@linaro.org> wrote:
>>
>> On 30/01/2024 04:32, Chen-Yu Tsai wrote:
>>> On Mon, Jan 29, 2024 at 3:34 PM Krzysztof Kozlowski
>>> <krzysztof.kozlowski@linaro.org> 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?



Best regards,
Krzysztof