I'm trying to figure out the best way to implement fb_setcolreg() for
FB_VISUAL_TRUECOLOR.
14 or so drivers copy/paste the CNVT_TOHW from skeletonfb.c:
#define CNVT_TOHW(val,width) ((((val)<<(width))+0x7FFF-(val))>>16)
...
red = CNVT_TOHW(red, info->var.red.length);
Another 18 or so drivers copy/paste a chan_to_field() function which has
a straightforward shift:
static inline u_int chan_to_field(u_int chan, struct fb_bitfield *bf)
{
chan &= 0xffff;
chan >>= 16 - bf->length;
return chan << bf->offset;
}
...
val = chan_to_field(red, &info->var.red);
Both methods return similar values, except that with CNVT_TOHW() the
extreme values seem to have a smaller range than the other values, while
with the chan_to_field() shift all the values have an equal range.
What's the reason behind choosing one over the other? Could/should a
common function be provided for all the drivers to use?
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