Re: 2.6 fbcon and 15/16 bpp

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> Here's a patch that fixed things on my machine.  I found it by trial and 
> error since I don't have a hardware reference document and the code is a 
> little confusing to me.  I don't know if this is the root cause or just 
> a fix for the symptoms.  Changing the u16's to u32's fixed the verticle 
> grille appearance and most of the color corruption.  Commenting out that 
> small block of code fixed the rest of the color problems.
> 
> I have a few questions.  Why are we going through the palette instead of 
> just writing the proper directcolor/truecolor bitvalues for that color?  
> Does that have to do with the disabled HW acceleration code?   Or is it 
> because the hw palette color components are 8 bits wide so the displayed 
> colors are more accurate?
> 
> And the code that I commented out, why is it accesing palette array 
> elements that have been set on a previous call or haven't been set yet?  
> Why is it trying to compensate for the wider green field when we're 
> programming 8 bit values to the hw palette?
> 
> My understanding of the low level video hardware control is very limited 
> beyond standard VGA register programming so I'm hoping to learn 
> something with all my questions.  :)
> 

Intersting. The pseudo palette thing might have to be u32 indeed, I have
to double check. That sounds like a typical misdesign crap vs. endian
assuming a given value can be accessed via any size is a little endian
"feature" that doesn't work on BE.

The HW palette stuff for 16 bits is fine afaik (well, i wrote it ;), and it
works for XFree. What color problems do you have fixed when you comment
it out ?

Ben.




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