Re: [PATCH v8 02/11] drm/fourcc: Add DRM_FORMAT_XV15/XV20

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

Hi Simon, Dave,

On 19/03/2026 17:15, Simon Ser wrote:
> What is the difference between DRM_FORMAT_XV15 and DRM_FORMAT_P030?

Good question. I thought the Cr & Cb are swapped between those formats.

The VC4 driver uses HVS_PIXEL_ORDER_XYCBCR define, and the comment in
drm_fourcc.h starts with "YCbCr420". So, CbCr. But then the comments
then continue with CrCb.

XV15/20 isn't super clear either, starting with "YCrCb" but then "Cb:Cr
plane".

The components in the plane descriptions look identical though, hinting
they are the same. So to be sure, I tested it:

I had test pattern support for XV15/20 in pykms, which I can test on a
Xilinx board. P030 is a bit more difficult, as on RPi5 it requires
DRM_FORMAT_MOD_BROADCOM_SAND128. But with a linear -> SAND128 converter,
I was able to test linear NV12 converted to NV12+SAND128 and shown on
the screen (just for reference), and similarly linear XV15 ->
P030+SAND128. And, indeed, the linear XV15 test pattern shows correctly
on screen when converted to SAND128. So afaics XV15 is indeed identical
to P030, and I can drop XV15.

This then brings up the question about XV20. That format doesn't exist
yet, but should it then be named similarly to P030? However, I have no
idea what P030 means, so I don't know what a 2x1 subsampled P030 would
be called...

Thoughts/ideas? Or just keep XV20?

 Tomi