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

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Chen-Yu Tsai <wenst@chromium.org>
Cc: Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	 Marcel Holtmann <marcel@holtmann.org>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	 Matthias Brugger <matthias.bgg@gmail.com>,
	 AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	 Sean Wang <sean.wang@mediatek.com>,
	linux-bluetooth@vger.kernel.org,  netdev@vger.kernel.org,
	linux-mediatek@lists.infradead.org,  devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: net: bluetooth: Add MediaTek MT7921S SDIO Bluetooth
Date: Mon, 5 Feb 2024 18:49:30 +0100	[thread overview]
Message-ID: <CAPDyKFofy24N7ymzTF7wiADc17Tw9FiNTYMnbxgoioMBwDKVhA@mail.gmail.com> (raw)
In-Reply-To: <CAGXv+5FwaNe7oesGwZ=yR0Pg82tEzEF3B0zjoex4qw+6zsSYbQ@mail.gmail.com>

On Wed, 31 Jan 2024 at 04:39, Chen-Yu Tsai <wenst@chromium.org> wrote:
>
> (+CC Ulf Hansson)
>
> On Wed, Jan 31, 2024 at 6:38 AM Rob Herring <robh@kernel.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@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?
>
> 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.

>
>
> 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