Re: [PATCHv2] dt: bindings: Add support for CSI1 bus

[Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>]

Hi,

On 19.01.2017 23:49, Sakari Ailus wrote:
> Hi Pavel,
>
> On Wed, Jan 11, 2017 at 11:53:35PM +0100, Pavel Machek wrote:
>> From: Sakari Ailus <sakari.ailus@iki.fi>
>>
>> In the vast majority of cases the bus type is known to the driver(s)
>> since a receiver or transmitter can only support a single one. There
>> are cases however where different options are possible.
>>
>> The existing V4L2 OF support tries to figure out the bus type and
>> parse the bus parameters based on that. This does not scale too well
>> as there are multiple serial busses that share common properties.
>>
>> Some hardware also supports multiple types of busses on the same
>> interfaces.
>>
>> Document the CSI1/CCP2 property strobe. It signifies the clock or
>> strobe mode.
>>
>> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
>> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
>> Signed-off-by: Pavel Machek <pavel@ucw.cz>
>>
>> diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
>> index 9cd2a36..08c4498 100644
>> --- a/Documentation/devicetree/bindings/media/video-interfaces.txt
>> +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
>> @@ -76,6 +76,11 @@ Optional endpoint properties
>>    mode horizontal and vertical synchronization signals are provided to the
>>    slave device (data source) by the master device (data sink). In the master
>>    mode the data source device is also the source of the synchronization signals.
>> +- bus-type: data bus type. Possible values are:
>> +  0 - MIPI CSI2
>> +  1 - parallel / Bt656
>> +  2 - MIPI CSI1
>> +  3 - CCP2
>
> Actually, thinking about this again --- we only need to explictly specify
> busses if we're dealing with either CCP2 or CSI-1. The vast majority of the
> actual busses are and continue to be CSI-2 or either parallel or Bt.656. As
> they can be implicitly detected, we would have an option to just drop values
> 0 and 1 from above, i.e. only leave CSI-1 and CCP2. For now, specifying
> CSI-2 or parallel / Bt.656 adds no value as the old DT binaries without
> bus-type will need to be supported anyway.
>
>>  - bus-width: number of data lines actively used, valid for the parallel busses.
>>  - data-shift: on the parallel data busses, if bus-width is used to specify the
>>    number of data lines, data-shift can be used to specify which data lines are
>> @@ -112,7 +117,8 @@ Optional endpoint properties
>>    should be the combined length of data-lanes and clock-lanes properties.
>>    If the lane-polarities property is omitted, the value must be interpreted
>>    as 0 (normal). This property is valid for serial busses only.
>> -
>> +- strobe: Whether the clock signal is used as clock or strobe. Used
>> +  with CCP2, for instance.
>
> How about the "ti,strobe-clock-inv" I proposed? No-one seems to know what
> this really truly means... or just drop it if it's not really needed.
>

Not really :), see 
https://www.spinics.net/lists/linux-media/msg99802.html and 
https://www.spinics.net/lists/linux-media/msg99800.html

"clock/strobe", and "strobe-inv" are two distinct properties, see 
CSI1B_CTRL description in OMAP TRM. BTW there is another property that 
is needed for both n900 cameras to operate correctly (VP_CLK_POL, bit 12 
from the same reg), but that can be added later on when we have the 
other bits in place.

Ivo