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

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Date: Tue, 30 Jan 2024 16:38:56 -0600
From: Rob Herring <robh@...nel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Chen-Yu Tsai <wenst@...omium.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	Luiz Augusto von Dentz <luiz.dentz@...il.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Sean Wang <sean.wang@...iatek.com>, linux-bluetooth@...r.kernel.org,
	netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: net: bluetooth: Add MediaTek MT7921S
 SDIO Bluetooth

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@...aro.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@...aro.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?

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.

Rob