linux-kernel - Re: [PATCH v5 1/2] Add OV5647 device tree documentation

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Date:   Mon, 12 Dec 2016 13:07:53 +0000
From:   Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>
To:     Sakari Ailus <sakari.ailus@....fi>,
        Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>
CC:     <mchehab@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <robh+dt@...nel.org>,
        <devicetree@...r.kernel.org>, <davem@...emloft.net>,
        <gregkh@...uxfoundation.org>, <geert+renesas@...der.be>,
        <akpm@...ux-foundation.org>, <linux@...ck-us.net>,
        <hverkuil@...all.nl>, <dheitmueller@...nellabs.com>,
        <slongerbeam@...il.com>, <lars@...afoo.de>,
        <robert.jarzmik@...e.fr>, <pavel@....cz>, <pali.rohar@...il.com>,
        <sakari.ailus@...ux.intel.com>, <mark.rutland@....com>,
        <CARLOS.PALMINHA@...opsys.com>
Subject: Re: [PATCH v5 1/2] Add OV5647 device tree documentation

Hi Sakari

On 12/12/2016 12:19 PM, Sakari Ailus wrote:
> Hi Ramiro,
> 
> On Mon, Dec 12, 2016 at 12:15:04PM +0000, Ramiro Oliveira wrote:
>> Hi Sakari
>>
>> On 12/12/2016 11:49 AM, Sakari Ailus wrote:
>>> Hi Ramiro,
>>>
>>> On Mon, Dec 12, 2016 at 11:39:31AM +0000, Ramiro Oliveira wrote:
>>>> Hi Sakari,
>>>>
>>>> Thank you for the feedback.
>>>>
>>>> On 12/7/2016 10:33 PM, Sakari Ailus wrote:
>>>>> Hi Ramiro,
>>>>>
>>>>> Thank you for the patch.
>>>>>
>>>>> On Mon, Dec 05, 2016 at 05:36:33PM +0000, Ramiro Oliveira wrote:
>>>>>> Add device tree documentation.
>>>>>>
>>>>>> Signed-off-by: Ramiro Oliveira <roliveir@...opsys.com>
>>>>>> ---
>>>>>>  .../devicetree/bindings/media/i2c/ov5647.txt          | 19 +++++++++++++++++++
>>>>>>  1 file changed, 19 insertions(+)
>>>>>>  create mode 100644 Documentation/devicetree/bindings/media/i2c/ov5647.txt
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/media/i2c/ov5647.txt b/Documentation/devicetree/bindings/media/i2c/ov5647.txt
>>>>>> new file mode 100644
>>>>>> index 0000000..4c91b3b
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/media/i2c/ov5647.txt
>>>>>> @@ -0,0 +1,19 @@
>>>>>> +Omnivision OV5647 raw image sensor
>>>>>> +---------------------------------
>>>>>> +
>>>>>> +OV5647 is a raw image sensor with MIPI CSI-2 and CCP2 image data interfaces
>>>>>> +and CCI (I2C compatible) control bus.
>>>>>> +
>>>>>> +Required properties:
>>>>>> +
>>>>>> +- compatible	: "ovti,ov5647";
>>>>>> +- reg		: I2C slave address of the sensor;
>>>>>> +
>>>>>> +The common video interfaces bindings (see video-interfaces.txt) should be
>>>>>> +used to specify link to the image data receiver. The OV5647 device
>>>>>> +node should contain one 'port' child node with an 'endpoint' subnode.
>>>>>> +
>>>>>> +Following properties are valid for the endpoint node:
>>>>>> +
>>>>>> +- data-lanes : (optional) specifies MIPI CSI-2 data lanes as covered in
>>>>>> +  video-interfaces.txt.  The sensor supports only two data lanes.
>>>>>
>>>>> Doesn't this sensor require a external clock, a reset GPIO and / or a
>>>>> regulator or a few? Do you need data-lanes, unless you can change the order
>>>>> or the number?
>>>>
>>>> In the setup I'm using, I'm not aware of any reset GPIO or regulator. I do use a
>>>> external clock but it's fixed and not controlled by SW. Should I add a property
>>>> for this?
>>>
>>> The sensor datasheet defines a power-up and power-down sequence for the
>>> device. If you don't implement these sequences in the driver on a DT based
>>> system, nothing suggests that they're implemented correctly. Could it be
>>> that the boot loader simply enables the regulators or another device
>>> requires them to be enabled?
>>>
>>> I presume at least the reset GPIO should be controlled explicitly in order
>>> to ensure correct function. Although hardware can be surprising: I have one
>>> production system that has no reset GPIO for the sensor albeit the sensor
>>> datasheet says that's part of the power up sequence.
>>>
>>
>> Sorry for the misunderstanding. I wanted to say that, there is no SW controlled
>> reset. In the board we're using to connect the sensor to our D-PHY we have a
>> GPIO controller that when it receives power, it removes the sensor from reset,
>> so I have no control over that.
> 
> Do you mean to say that there's a GPIO controller but there's not (yet?) a
> driver for that or that the reset line is actually hard-wired to something
> else?
> 

The reset line is hardwired to a GPIO controller that when powered-on removes
the sensor from reset. However I have no control over the GPIO controller.

>>
>> Regarding the clock, should I create a new property?
> 
> Yes. The sensor does require a clock.
> 
>>
>> And also, regarding the data-lanes, AFAIK it isn't possible to change the order
>> of the data and clock lanes so should I remove that property?
> 
> Sounds good to me.
> 
>>
>>>>
>>>>>
>>>>> An example DT snippet wouldn't hurt.
>>>>
>>>> Sure, I can add a example snippet.
>>>>
>>>>>
>>>>
>>>
>> --
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>