Question about original PSP hardware

[akira]

Do PSP games set their internal rendering resolution themselves? Or is it completely handled/done by the PSP itself? Along with other graphic effects like anti-aliasing, shadows/motion blur/bloom etc.?

I've always wondered this when emulating, why PPSSPP only multiples the rendering resolution by x2, x4, etc instead of native screen-matching resolutions like 2560x1440.