Re: Choosing the correct framebuffer configuration

["Michel Dänzer" <michel@daenzer.net>]

On Sun, 2005-08-07 at 11:33 -0400, Jon Smirl wrote:
> On 8/7/05, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Fri, 5 Aug 2005, Jon Smirl wrote:
> > > The chips actually allow nine configs (maybe more when I get a look at
> > > the R300 doc). It is ambiguous to set these configs based on BPP since
> > > there are multiple configs for various BPP. These configs should
> > > instead be set with the transp/red/blue/green fields.
> > >
> > > 4bpp Index = /4
> > > 8bpp Index = /8
> > > 16bpp aRGB 1555 = 1/5/5/5
> > > 16bpp RGB 565 = /5/6/5
> > > 16bpp aRGB 4444 = 4/4/4/4
> > > 16bpp aIndex 88 = 8/8
> > > 24bpp RGB 888 = /8/8/8
> > > 32bpp aRGB 8888 = 8/8/8/8
> > > 32bpp aRGB 2:10:10:10 = 2/10/10/10
> > >
> > > What is the best way to fix this?
> > 
> > Just follow the FBIOPUT_VSCREENINFO rules:
> >   - If a value doesn't fit, round it up.
> >   - If rounding is impossible, return an error.
> > 
> > So if a user asks for e.g. bpp 16, transp.length = 1,
> > {red,green,blue}.length = 0, you can give him 1555 if your hardware supports
> > it. Or 4444 if your hardware doesn't support anything in between 1000 and 4444
> > (w.r.t. rounding). But you must not give him 565, since this implies you
> > rounded down transp.length.
> > 
> > > The interesting hidden config is 30b color.
> > 
> > Piece of cake!
> > 
> >     bpp = 32
> >     transp.length = 2, {red,green,blue}.length = 10
> 
> The problem is that the radeonfb driver sees bpp = 32 and then sets
> rgbt = 8/8/8/8. It stomps rgbt without looking at it.

Looks like a radeonfb bug.


> The basic problem is what happens if bpp and rgbt are set in
> conflicting ways. For example bpp = 16 and rgbt = 8/8/8/8. Which one
> should win?

Read what you quoted from Geert above.


-- 
Earthling Michel Dänzer      |     Debian (powerpc), X and DRI developer
Libre software enthusiast    |   http://svcs.affero.net/rm.php?r=daenzer


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