Date: Tue, 20 Feb 2024 16:19:18 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Ulf Hansson <ulf.hansson@...aro.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, Feb 6, 2024 at 1:50 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Wed, 31 Jan 2024 at 04:39, Chen-Yu Tsai <wenst@...omium.org> wrote:
> >
> > (+CC Ulf Hansson)
> >
> > On Wed, Jan 31, 2024 at 6:38 AM Rob Herring <robh@...nel.org> 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@...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?
> >
> > 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.
>
> Yes, that's what we decided to go with, a long time ago. At least in
> this particular case, I think it makes sense, as each function
> (child-node) may also describe additional resources routed to each
> function.
>
> A typical description could be for a WiFi-Bluetooth combo-chip, where
> each function may have its own clocks, irqs and regulators being
> routed.

Rob, Krzysztof, does that help you understand why the binding and example
are written with bluetooth being one node and WiFi (should it ever be added)
being a separate node? It is based on the existing MMC controller bindings.

ChenYu


> >
> >
> > 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
>
> Kind regards
> Uffe

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