> Plymouth shouldn't get the values with drmModeCrtcGetGamma — there's no
> guarantee that the CLUT contains suitable values at that point (e.g. the
> hardware could currently be programmed for a different colour bit depth
> in the first place).
Ok, but at this point I wonder (sorry, not really familiar with libdrm) why the
value reported by drmModeCrtcGetGamma are not coherent with the values
currently programmed in hardware. Is this a common thing?

If __immediately__ before drmModeSetCrtc I do drmModeCrtcGetGamma +
drmModeCrtcSetGamma with the values retrieved, everything works fine with the
correct colors, so the CLUTs returned by drmModeCrtcGetGamma actually contain
suitable / correct values but apparently these are different from what is
programmed in the hardware.