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Subject: Re: [PATCH 07/12] dt-bindings: tc358754: add DT bindings
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Maciej Purski <m.purski@samsung.com>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, devicetree@vger.kernel.org,
        dri-devel@lists.freedesktop.org, David Airlie <airlied@linux.ie>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Kukjin Kim <kgene@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Archit Taneja <architt@codeaurora.org>,
        Inki Dae <inki.dae@samsung.com>,
        Joonyoung Shim <jy0922.shim@samsung.com>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
From:   Andrzej Hajda <a.hajda@samsung.com>
Date:   Wed, 30 May 2018 15:07:29 +0200
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On 30.05.2018 14:35, Laurent Pinchart wrote:
> Hi Andrzej,
>
> On Wednesday, 30 May 2018 12:59:12 EEST Andrzej Hajda wrote:
>> On 28.05.2018 12:18, Laurent Pinchart wrote:
>>> On Monday, 28 May 2018 12:47:11 EEST Maciej Purski wrote:
>>>> The patch adds bindings to Toshiba DSI/LVDS bridge TC358764.
>>>> Bindings describe power supplies, reset gpio and video interfaces.
>>>>
>>>> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
>>>> Signed-off-by: Maciej Purski <m.purski@samsung.com>
>>>> ---
>>>>
>>>>  .../bindings/display/bridge/toshiba,tc358764.txt   | 42 ++++++++++++++++
>>>>  1 file changed, 42 insertions(+)
>>>>  create mode 100644
>>>>
>>>> Documentation/devicetree/bindings/display/bridge/toshiba,tc358764.txt
>>>>
>>>> diff --git
>>>> a/Documentation/devicetree/bindings/display/bridge/toshiba,tc358764.txt
>>>> b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358764.txt
>>>> new
>>>> file mode 100644
>>>> index 0000000..d09bdc2
>>>> --- /dev/null
>>>> +++
>>>> b/Documentation/devicetree/bindings/display/bridge/toshiba,tc358764.txt
>>>> @@ -0,0 +1,42 @@
>>>> +TC358764 MIPI-DSI to LVDS panel bridge
>>>> +
>>>> +Required properties:
>>>> +  - compatible: "toshiba,tc358764"
>>>> +  - reg: the virtual channel number of a DSI peripheral
>>>> +  - vddc-supply: core voltage supply
>>>> +  - vddio-supply: I/O voltage supply
>>>> +  - vddmipi-supply: MIPI voltage supply
>>>> +  - vddlvds133-supply: LVDS1 3.3V voltage supply
>>>> +  - vddlvds112-supply: LVDS1 1.2V voltage supply
>>> That's a lot of power supplies. Could some of them be merged together ?
>>> See https://patchwork.freedesktop.org/patch/216058/ for an earlier
>>> discussion on the same subject.
>> Specs says about 3 supply voltage values:
>> - 1.2V - digital core, DSI-RX PHY
>> - 1.8-3.3V - digital I/O
>> - 3.3V - LVDS-TX PHY
>>
>> So I guess it should be minimal number of supplies. Natural candidates:
>>
>> - vddc-supply: core voltage supply, 1.2V
>> - vddio-supply: I/O voltage supply, 1.8V or 3.3V
>> - vddlvds-supply: LVDS1/2 voltage supply, 3.3V
>>
>> I have changed name of the latest supply to be more consistent with
>> other supplies, and changed 1.8-3.3 (which incorrectly suggest voltage
>> range), to more precise voltage alternative.
> This looks fine to me.
>
>>>> +  - reset-gpios: a GPIO spec for the reset pin
>>>> +
>>>> +The device node can contain zero to two 'port' child nodes, each with
>>>> one
>>>> +child
>>>> +'endpoint' node, according to the bindings defined in [1].
>>>> +The following are properties specific to those nodes.
>>>> +
>>>> +port:
>>>> +  - reg: (required) can be 0 for DSI port or 1 for LVDS port;
>>> This seems pretty vague to me. It could be read as meaning that ports are
>>> completely optional, and that the port number you list can be used, but
>>> that something else could be used to.
>>>
>>> Let's make the port nodes mandatory. I propose the following.
>>>
>>> Required nodes:
>>>
>>> The TC358764 has DSI and LVDS ports whose connections are described using
>>> the OF graph bindings defined in
>>> Documentation/devicetree/bindings/graph.txt. The device node must contain
>>> one 'port' child node per DSI and LVDS port. The port nodes are numbered
>>> as follows.
>>>
>>>   Port                  Number
>>> -------------------------------------------------------------------
>>>   DSI Input             0
>>>   LVDS Output           1
>>>
>>> Each port node must contain endpoint nodes describing the hardware
>>> connections.
>> Since the bridge is controlled via DSI bus, DSI input port is not necessary.
> I don't agree with this. Regardless of how the bridge is controlled, I think 
> we should always use ports to describe the data connections. Otherwise it 
> would get more complicated for display controller drivers to use different 
> types of bridges.


It was discussed already, and DT guideline is to skip graphs in simple
case of parent/child nodes, see for example [1].

[1]: https://marc.info/?l=dri-devel&m=148354108702517&w=2

Regards
Andrzej

>>>> +[1]: Documentation/devicetree/bindings/media/video-interfaces.txt
>>>> +
>>>> +Example:
>>>> +
>>>> +	bridge@0 {
>>>> +		reg = <0>;
>>>> +		compatible = "toshiba,tc358764";
>>>> +		vddc-supply = <&vcc_1v2_reg>;
>>>> +		vddio-supply = <&vcc_1v8_reg>;
>>>> +		vddmipi-supply = <&vcc_1v2_reg>;
>>>> +		vddlvds133-supply = <&vcc_3v3_reg>;
>>>> +		vddlvds112-supply = <&vcc_1v2_reg>;
>>>> +		reset-gpios = <&gpd1 6 GPIO_ACTIVE_LOW>;
>>>> +		#address-cells = <1>;
>>>> +		#size-cells = <0>;
>>>> +		port@1 {
>>>> +			reg = <1>;
>>>> +			lvds_ep: endpoint {
>>>> +				remote-endpoint = <&panel_ep>;
>>>> +			};
>>>> +		};
>>>> +	};