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SubjectRe: [PATCH v4 2/2] media: dt-bindings: media: st,stm32-dcmi: Add support of BT656
Date
Hi Sakari,

On 10/21/20 3:00 PM, Sakari Ailus wrote:
> Hi Hugues,
>
> On Tue, Oct 20, 2020 at 12:14:49PM +0200, Hugues Fruchet wrote:
>> Add support of BT656 parallel bus mode in DCMI.
>> This mode is enabled when hsync-active & vsync-active
>> fields are not specified.
>>
>> Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
>> ---
>> .../devicetree/bindings/media/st,stm32-dcmi.yaml | 30 ++++++++++++++++++++++
>> 1 file changed, 30 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
>> index 3fe778c..1ee521a 100644
>> --- a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
>> +++ b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
>> @@ -44,6 +44,36 @@ properties:
>> bindings defined in
>> Documentation/devicetree/bindings/media/video-interfaces.txt.
>>
>> + properties:
>> + endpoint:
>> + type: object
>> +
>> + properties:
>> + bus-width: true
>> +
>> + hsync-active:
>> + description:
>> + If both HSYNC and VSYNC polarities are not specified, BT656
>> + embedded synchronization is selected.
>> + default: 0
>> +
>> + vsync-active:
>> + description:
>> + If both HSYNC and VSYNC polarities are not specified, BT656
>> + embedded synchronization is selected.
>> + default: 0
>
> Should I understand this as if the polarities were not specified, BT.656
> will be used?

Yes, this is what is documented in video-interfaces.txt:
"
Note, that if HSYNC and VSYNC polarities are not specified, embedded
synchronization may be required, where supported.
"
and
"
/* If hsync-active/vsync-active are missing,
embedded BT.656 sync is used */
hsync-active = <0>; /* Active low */
vsync-active = <0>; /* Active low */
"
and I found also this in
Documentation/devicetree/bindings/media/renesas,vin.yaml
"
hsync-active:
description:
If both HSYNC and VSYNC polarities are not specified,
embedded
synchronization is selected.
default: 1

vsync-active:
description:
If both HSYNC and VSYNC polarities are not specified,
embedded
synchronization is selected.
default: 1
"

In the other hand I've found few occurences of "bus-type"
(marvell,mmp2-ccic.yaml), it is why I asked you if "bus-type" is the new
way to go versus previous way to signal BT656 (without hsync/vsync) ?
As explained previously, I prefer this last way for backward compatibility.


The bindings previously documented BT.601 (parallel) only, so
> it was somewhat ambigious to begin with. Is there a risk of interpreting
> old BT.601 bindings as BT.656?
I don't think so.

With bus-type property, I believe you could
> avoid at least that risk.
yes but as explained, I'll prefer not to amend current boards device
tree files.

>
> Also not specifying at least one of the default values leads to BT.656
> without bus-type. That could be addressed by removing the defaults.
>
I'm new to yaml, I've taken that from renesas,vin.yaml. Should I just
drop the "default: 1" lines ?

>> +
>> + pclk-sample: true
>> +
>> + remote-endpoint: true
>> +
>> + required:
>> + - remote-endpoint
>> +
>> + additionalProperties: false
>> +
>> + additionalProperties: false
>> +
>> required:
>> - compatible
>> - reg
>

BR,
Hugues.
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