[Linux-fbdev-devel] setcolreg vs. 565

[Benjamin H. <be...@ke...>]

While working on radeonfb, I figured out there is something we
probably don't handle properly in it nor in aty128fb, and I'm
actually not sure how we should handle it API-wise with 565.

For 8 bits, 5:5:5 and 24 bits, there is no problem, each
color component has the same size. 8 and 24 bits takes regno
values ranging from 0 to 255, while 5:5:5 takes regno values
ranging from 0 to 31 (internally expanded to 0..255).

For 5:6:5 things are slightly different since R and B have
a 0..31 range while G ranges from 0..63. In the DAC, the ATI
chip right-align these, so a given regno is actually split
into regno<<3 for R and B values and regno<<2 for G. However,
that means we should expose to userland a 64 entries cmap
instead of 32, am I wrong ? In this case however, when setting
cmap for regno 32..63, we should ignore R and B and only use
G, or did I miss something ?

Ben.