Re: Choosing the correct framebuffer configuration

On 8/7/05, Michel Dänzer [off-list ref] wrote:

On Sun, 2005-08-07 at 11:33 -0400, Jon Smirl wrote:

quoted

On 8/7/05, Geert Uytterhoeven [off-list ref] wrote:

quoted

On Fri, 5 Aug 2005, Jon Smirl wrote:

quoted

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.

quoted

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.

quoted

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.

I'm just verifying everything before changing things. Sometimes there
are disagreements on what rules we should be following.

So from Geert's rules 16bpp doesn't fit with 8/8/8/8 so round it up to
32bpp. Are we sure that is what applications are expecting to happen?

-- 
Jon Smirl
jonsmirl@gmail.com


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