Re: [PATCH 3/6] media: videodev2.h: Add macro V4L2_FIELD_IS_SEQUENTIAL

[Steve Longerbeam <slongerbeam@gmail.com>]

On 05/25/2018 05:10 PM, Nicolas Dufresne wrote:
> (in text this time, sorry)
>
> Le vendredi 25 mai 2018 à 16:53 -0700, Steve Longerbeam a écrit :
>> Add a macro that returns true if the given field type is
>> 'sequential',
>> that is, the data is transmitted, or exists in memory, as all top
>> field
>> lines followed by all bottom field lines, or vice-versa.
>>
>> Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
>> ---
>>   include/uapi/linux/videodev2.h | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/include/uapi/linux/videodev2.h
>> b/include/uapi/linux/videodev2.h
>> index 600877b..408ee96 100644
>> --- a/include/uapi/linux/videodev2.h
>> +++ b/include/uapi/linux/videodev2.h
>> @@ -126,6 +126,10 @@ enum v4l2_field {
>>   	 (field) == V4L2_FIELD_INTERLACED_BT ||\
>>   	 (field) == V4L2_FIELD_SEQ_TB ||\
>>   	 (field) == V4L2_FIELD_SEQ_BT)
>> +#define V4L2_FIELD_IS_SEQUENTIAL(field) \
>> +	((field) == V4L2_FIELD_SEQ_TB ||\
>> +	 (field) == V4L2_FIELD_SEQ_BT ||\
>> +	 (field) == V4L2_FIELD_ALTERNATE)
> No, alternate has no place here, in alternate mode each buffers have
> only one field.

Then I misunderstand what is meant by "alternate". The name implies
to me that a source sends top or bottom field alternately, or top/bottom
fields exist in memory buffers alternately, but with no information about
which field came first. In other words, "alternate" is either seq-tb or 
seq-bt,
without any info about field order.

If it is just one field in a memory buffer, why isn't it called
V4L2_FIELD_TOP_OR_BOTTOM, e.g. we don't know which?

Steve