Re: [PATCH 1/2] media: dt-bindings: Add Intersil ISL7998x DT bindings

[Marek Vasut <marex@denx.de>]

On 5/29/19 1:15 PM, Ian Arkver wrote:
> Hi Marek,
> 
> On 29/05/2019 12:09, Marek Vasut wrote:
>> On 5/29/19 1:04 PM, Ian Arkver wrote:
>>> Hi,
>>>
>>> On 29/05/2019 11:41, Marek Vasut wrote:
>>>> On 5/29/19 8:28 AM, Jacopo Mondi wrote:
>>>>
>>>> [...]
>>>>
>>>>>>>>> [1]
>>>>>>>>> https://www.renesas.com/eu/en/products/audio-video/video-decoders-encoders/video-decoders/device/ISL79987.html
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> +Required Properties:
>>>>>>>>>> +- compatible: value should be "isil,isl79987"
>>>>>>>
>>>>>>> And here you might want to have 2 different compatibles for 79987
>>>>>>> and
>>>>>>> 79988.
>>>>>>
>>>>>> The 79988 is not supported yet, do we want to have it in the binding
>>>>>> doc?
>>>>>>
>>>>>
>>>>> I got mislead by the isl7998x naming scheme you used...
>>>>>
>>>>> I would say that's up to you, the two chips seems very similar,
>>>>> and it might make sense to provide bindings that support both. At the
>>>>> same time, as long as the here defined bindings does not prevent
>>>>> future expansions to include the ISL79988, its support could be safely
>>>>> post-poned. In that case please s/isl7998x/isl79987/ in this document
>>>>> and do not mention BT565 in the description.
>>>>
>>>> Right
>>>>
>>>>>> [...]
>>>>>>
>>>>>>>>> I see from the example you only support one output port? How do
>>>>>>>>> you
>>>>>>>>> model the input ones.
>>>>>>>>
>>>>>>>> I don't . Do we model analog inputs now somehow ?
>>>>>>>
>>>>>>> I really think so, please see:
>>>>>>> Documentation/devicetree/bindings/display/connector/analog-tv-connector.txt
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> And as an example of a board device tree using connectors to model
>>>>>>> analog input see how the cvbs input on Salvator-X is described:
>>>>>>>
>>>>>>>      cvbs-in {
>>>>>>>          compatible = "composite-video-connector";
>>>>>>>          label = "CVBS IN";
>>>>>>>
>>>>>>>          port {
>>>>>>>              cvbs_con: endpoint {
>>>>>>>                  remote-endpoint = <&adv7482_ain7>;
>>>>>>>              };
>>>>>>>          };
>>>>>>>      };
>>>>>>>
>>>>>>> I think you should provide 4 input ports, where to connect input
>>>>>>> from
>>>>>>> the analog connectors, and derive the number of enabled inputs from
>>>>>>> the number of endpoints connected to an active remote.
>>>>>>
>>>>>> Deriving the number of active physical inputs from some existing
>>>>>> binding
>>>>>> makes sense.
>>>>>>
>>>>>> However unlike the adv7482, the isl79987 does not support
>>>>>> remapping the
>>>>>> physical inputs to ADCs in the chip. It does support some
>>>>>> remapping of
>>>>>> physical inputs to MIPI CSI2 channels, but that's probably not very
>>>>>> useful.
>>>>>>
>>>>>
>>>>> I understand, but I will now use against you the argument you have
>>>>> correctly pointed out here below that DT should describe hardware, and
>>>>> the hardware has indeed 4 input ports..
>>>>
>>>> My question here is whether it makes sense to describe the ports
>>>> even if
>>>> they cannot be muxed to different ADC. Does it ?
>>>
>>> Each input port can be either differential CVBS or single ended with a
>>> 2:1 input select mux. It would be nice to be able to describe this.
>>
>> Where do you see that ?
> 
> Bits 0 and 1 of each channel page's Differential Clamping Control 4
> (0x39, ISL7998x_REG_Px_DEC_DIFF_CLMP_CTL_4).
> 
> I don't think you change it from the default (single ended on the first
> input).

I don't, since I have no way to test the differential mode of operation.

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