Re: [Linux-fbdev-devel] Re: [PATCH] Radeon frame buffer driver

[Antonino D. <ad...@us...>]

On Wed, 2002-04-10 at 21:14, Geert Uytterhoeven wrote:
> On Wed, 10 Apr 2002, Peter Horton wrote:
> > On Wed, Apr 10, 2002 at 01:06:09PM +0200, Geert Uytterhoeven wrote:
> > > On Wed, 10 Apr 2002, Peter Horton wrote:
> > > > 
> > > > The colour map is only used by the kernel and the kernel only uses 16
> > > > entries so there isn't any reason to waste memory by making it any
> > > > larger. I checked a few other drivers and they do the same (aty128fb for
> > > > one).
> > > 
> > > However, this change will make the driver not save/restore all color map
> > > entries on VC switch in graphics mode.
> > 
> > Well I thought this didn't matter because if we only use 16 entries they
> > will all be saved / restored. But there is a problem because the copy of
> > the entire palette that we keep is per card and will be lost on VC
> > switch, though the kernel will restore the first 16 entries.  Really we
> > need to keep a copy of the relevant part of the palette for each display
> > (256 for 8bpp, 32 for 15 bit mode, 64 for 16bpp and 256 for 32bpp).
> > Looking at a handful of drivers this seems to be a common error, so it
> > can't be causing users much grief. I don't think changing the size of
> > the colour map fixes this though (I need to look at the code when I get
> > home).
> 
I think most drivers do save/restore the entire colormap, at least the
vesafb.  From what I can understand from the code, the display->dispsw
which is a 16- or 17-entry palette is primarily used by the console, but
is just a subset of display->cmap, which is an arbitrarily sized
colormap.  Also display->cmap can be set by applications from userspace
and can be saved on a per console basis.  Most drivers have a
do_install_cmap in set_var or fbcon_switch which effectively restores
the hardware CLUT registers from display->cmap, aside from restoring
display->dispsw.  The vesafb also does an addistional save of the old
colormap (using fb_get_cmap) before installing the new colormap.

This is just based on how I understand the code, so correct me if I'm
wrong.

Tony