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Message-Id: <20180530130731eucas1p160d53c3f8500bcecd000bd8895843817~zbgGgQw3b1079710797eucas1p1H@eucas1p1.samsung.com>
Date: Wed, 30 May 2018 15:07:29 +0200
From: Andrzej Hajda <a.hajda@...sung.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Maciej Purski <m.purski@...sung.com>, 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 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@...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.
> 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>;
>>>> + };
>>>> + };
>>>> + };
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