May somewhat interesting for others. The Color Space Conversion can be somewhat missused to do RGB -> RGB. I barely spent any time on it, but the following coefficients
A1=0x100, A2=0, A3=0, B1=0, B2=0x100, B3=0, C1=0, C2=0, C3=0x100, D1=0, D2=0x100, D3=0x100
seem to lead to the same output as
CSC0_CTRL = 1 (the bypass mode)
Unfortunately NXP does not fully document what the conversion are doing. But with adjusting this coefficients, I at least I was able to do a slight color correction for a display we use. Is this an ugly hack, yes absolutely, did it solve my problem, yes.
#!/usr/bin/env python3
import mmap
import struct
def write_word(address, value):
with open('/dev/mem', 'r+b') as f:
mem = mmap.mmap(f.fileno(), mmap.PAGESIZE, mmap.MAP_SHARED, mmap.PROT_READ | mmap.PROT_WRITE, offset=address & ~(mmap.PAGESIZE - 1))
struct.pack_into('I', mem, address & (mmap.PAGESIZE - 1), value)
mem.close()
def write_coeffs(a1, a2, a3, b1, b2, b3, c1, c2, c3, d1, d2, d3):
# LCDIF2 = 0x32E90000
# A1-C3 11-bits, D1-D3 10 bits
def w(x, y):
return ((x & 0x3FF) << 16) | ((y & 0x3FF) << 0)
write_word(0x32E9021C, 0) # CSC0_CTRL
write_word(0x32E90220, w(a2, a1)) # CSC0_COEF0 - A2 A1
write_word(0x32E90224, w(b1, a3)) # CSC0_COEF1 - B1 A3
write_word(0x32E90228, w(b3, b2)) # CSC0_COEF2 - B3 B2
write_word(0x32E9022C, w(c2, c1)) # CSC0_COEF3 - C2 C1
write_word(0x32E90230, w(d1, c3)) # CSC0_COEF4 - D1 C3
write_word(0x32E90234, w(d3, d2)) # CSC0_COEF5 - D3 D2
write_coeffs(0x100, 0, 0, 0, 0x100, 0, 0, 0, 0x100, 0x000, 0x100, 0x100) # "somewhat" close to identity
write_coeffs(0x0B0, 0, 0, 0, 0x100, 0, 0, 0, 0x100, 0x000, 0x100, 0x100) # less red
