Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module

[Hugues FRUCHET <hugues.fruchet@st.com>]

On 06/23/2017 12:25 PM, H. Nikolaus Schaller wrote:
> Hi Hugues,
> 
>> Am 22.06.2017 um 17:05 schrieb Hugues Fruchet <hugues.fruchet@st.com>:
>>
>> From: "H. Nikolaus Schaller" <hns@goldelico.com>
>>
>> This adds documentation of device tree bindings
>> for the OV965X family camera sensor module.
>>
>> Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
>> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
>> ---
>> .../devicetree/bindings/media/i2c/ov965x.txt       | 37 ++++++++++++++++++++++
>> 1 file changed, 37 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/media/i2c/ov965x.txt
>>
>> diff --git a/Documentation/devicetree/bindings/media/i2c/ov965x.txt b/Documentation/devicetree/bindings/media/i2c/ov965x.txt
>> new file mode 100644
>> index 0000000..0e0de1f
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/media/i2c/ov965x.txt
>> @@ -0,0 +1,37 @@
>> +* Omnivision OV9650/9652/9655 CMOS sensor
>> +
>> +The Omnivision OV965x sensor support multiple resolutions output, such as
>> +CIF, SVGA, UXGA. It also can support YUV422/420, RGB565/555 or raw RGB
>> +output format.
>> +
>> +Required Properties:
>> +- compatible: should be one of
>> +	"ovti,ov9650"
>> +	"ovti,ov9652"
>> +	"ovti,ov9655"
>> +- clocks: reference to the mclk input clock.
> 
> I wonder why you have removed the clock-frequency property?
> 
> In some situations the camera driver must be able to tell the clock source
> which frequency it wants to see.
> 
> For example we connect the camera to an OMAP3-ISP (image signal processor) and
> there it is assumed that camera modules know the frequency and set the clock, e.g.:
> 
> http://elixir.free-electrons.com/linux/v4.4/source/Documentation/devicetree/bindings/media/i2c/nokia,smia.txt#L52
> http://elixir.free-electrons.com/linux/v3.14/source/Documentation/devicetree/bindings/media/i2c/mt9p031.txt
> 
> If your clock is constant and defined elsewhere we should make this
> property optional instead of required. But it should not be missing.
> 
> Here is a hack to get it into your code:
> 
> http://git.goldelico.com/?p=gta04-kernel.git;a=blobdiff;f=drivers/media/i2c/ov9650.c;h=b7ab46c775b9e40087e427ae0777e9f7c283694a;hp=1846bcbb19ae71ce686dade320aa06ce2e429ca4;hb=ca85196f6fd9a77e5a0f796aeaf7aa2cde60ce91;hpb=8a71f21b75543a6d99102be1ae4677b28c478ac9
> 

Here is how it is used on my DT, the camera clock is a fixed crystal 24M 
clock:

+	clocks {
+		clk_ext_camera: clk-ext-camera {
+			#clock-cells = <0>;
+			compatible = "fixed-clock";
+			clock-frequency = <24000000>;
+		};
+	};
[...]
+	ov9655: camera@30 {
+		compatible = "ovti,ov9655";
+		reg = <0x30>;
+		pwdn-gpios = <&gpioh 13 GPIO_ACTIVE_HIGH>;
+		clocks = <&clk_ext_camera>;
+		status = "okay";
+
+		port {
+			ov9655_0: endpoint {
+				remote-endpoint = <&dcmi_0>;
+			};
+		};
+	};


>> +
>> +Optional Properties:
>> +- resetb-gpios: reference to the GPIO connected to the resetb pin, if any.
>> +- pwdn-gpios: reference to the GPIO connected to the pwdn pin, if any.
> 
> Here I wonder why you did split that up into two gpios. Each "*-gpios" can have
> multiple entries and if one is not used, a 0 can be specified to make it being ignored.
> 
> But it is up to DT maintainers what they prefer: separate single gpios or a single gpio array.

I have followed the ov2640 binding, which have the same pins naming 
(resetb/pwdn).
As far as I see, separate single gpios are commonly used in
Documentation/devicetree/bindings/media/i2c/

> 
> 
> What I am missing to support the GTA04 camera is the control of the optional "vana-supply".
> So the driver does not power up the camera module when needed and therefore probing fails.
> 
>    - vana-supply: a regulator to power up the camera module.
> 
> Driver code is not complex to add:
> 
> http://git.goldelico.com/?p=gta04-kernel.git;a=blobdiff;f=drivers/media/i2c/ov9650.c;h=1846bcbb19ae71ce686dade320aa06ce2e429ca4;hp=c0819afdcefcb19da351741d51dad00aaf909254;hb=8a71f21b75543a6d99102be1ae4677b28c478ac9;hpb=6db55fc472eea2ec6db03833df027aecf6649f88

Yes, I saw it in your code, but as I don't have any programmable power 
supply on my setup, I have not pushed this commit.
And I also don't have a clock to enable/disable -fixed clock-, I need to 
check the behaviour when disabling/enabling a fixed clock, I will give 
it a try.

> 
>> +
>> +The device node must contain one 'port' child node for its digital output
>> +video port, in accordance with the video interface bindings defined in
>> +Documentation/devicetree/bindings/media/video-interfaces.txt.
>> +
>> +Example:
>> +
>> +&i2c2 {
>> +	ov9655: camera@30 {
>> +		compatible = "ovti,ov9655";
>> +		reg = <0x30>;
>> +		pwdn-gpios = <&gpioh 13 GPIO_ACTIVE_HIGH>;
>> +		clocks = <&clk_ext_camera>;
>> +
>> +		port {
>> +			ov9655: endpoint {
>> +				remote-endpoint = <&dcmi_0>;
>> +			};
>> +		};
>> +	};
>> +};
>> -- 
>> 1.9.1
>>
> 
> BR and thanks,
> Nikolaus
>