Sorry for the delay in replying. I'm on holiday at the moment.

> Hmm, but maybe generic raspos handler requires only "bit per pixel,"
> doesn't it? "The actually significant number of bits" is provided
> by info of each color in other members, I think.

I was thinking of the TC mfb, which is mono but uses byte addressing.
Only the lowest bit is significant (so depth of 1 and bpp of 8). Are
there other devices like that?

> > - a flag to indicate whether the frame buffer is simple and can be
> > handled by mfb/cfb or is something a bit different, like a VGA or
> > PixelStamp?
>
> I think such device specific features could be determined by
> WSDISPLAYIO_GTYPE.

It may not be possible to drive certain types of display with the
usual code (as is the case with the PixelStamp, no direct FB access).
Rather than teaching the X server about each of the black sheep, why
not have a flag passed down by the kernel?

> > - a flag to indicate whether or not colormap changes are accepted?
> >   Not entirely necessary, but nice to have.
>
> Can't we check it by a return value of WSDISPLAYIO_GETCMAP or
> WSDISPLAYIO_PUTCMAP?

I agree with your suggestion here.

Andrew