linux-kernel - Re: [PATCH 07/12] dt-bindings: tc358754: add DT bindings

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Date:   Wed, 30 May 2018 11:59:12 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Maciej Purski <m.purski@...sung.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Archit Taneja <architt@...eaurora.org>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH 07/12] dt-bindings: tc358754: add DT bindings

On 28.05.2018 12:18, Laurent Pinchart wrote:
> Hi Maciej,
>
> Thank you for the patch.
>
> 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@...sung.com>
>> Signed-off-by: Maciej Purski <m.purski@...sung.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.


>
>> +  - 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.

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>;
>> +			};
>> +		};
>> +	};