> This could be output encoder specific; I'm not aware of such limitation, so I'm looking into Intel docs now (TGL ones, volume 12: Display Engine), cannot find any mention of it. Would you have any pointers?

> Or do you mean specifically GPU (texture) scaling? I'm not that familiar with GPU part, but I would be surprised if that was true, when the hardware today considers LUTs for the buffers.

To scale in linear RGB colorspace, you first need to do a colorspace transform on the entire buffer, then scale, then do another colorspace transform. I can't find any device that does this in a single step correctly, except for some rare GPU extensions.