Re: [Linux-fbdev-devel] Re: [PATCH] fbdev: colormap fixes

["Antonino A. Daplas" <adaplas@gmail.com>]

Jon Smirl wrote:
> On 7/28/05, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Thu, 28 Jul 2005, Jon Smirl wrote:
> > > I've verified now that all ATI R300+ chips have 10bit cmaps. These are
> > > pretty common so I'd be in favor of making this into a binary
> > > attribute where I can get/set the whole table at once. Given that
> > > OpenGL is already supporting 12 and 16 bits these tables are only
> > > going to get much larger.
> > >
> > > 1024 entries * 5 fields * 2 bytes = 10KB -- too big for a text attribute.
> > >
> > > 65536 entries * 5 fields * 2 bytes = 655KB -- way too big for a text attribute.
> > >
> > > The bits_per_pixel sysfs attribute is an easy way to tell how many
> > > entries you need. You can just set it at 4, 8, 10, etc until you get
> > > an error. Now you know the max. 2^n and you know how many entries.
> > No, bits_per_pixel can be (much) larger than the color map size. E.g. a simple
> > ARGB8888 directcolor mode has bits_per_pixel = 32 and color map size = 256.
>
> So I have the bits_per_pixel attribute wrong in sysfs. It needs to be
> bits_per_color and then let the driver sort it out.  Otherwise there
> is no way to set ARGB8888 versus ARGB2101010. With bits per color you
> would set 8 or 10.

No, you have to add another attribute for {transp|red|green|blue}.{len,offset}
and another attribute for the pixelformat. Then using those, one can
easily deduce the cmap size.

> If that isn't good enough I can switch the attribute to take strings
> like ARGB8888.

Please no.

> What do you think, should I just switch to fbconfig names and a binary
> cmap attribute?

Does a binary attribute not have the same buffer size limitation as
the text attribute?  I really don't know, just asking.

Tony
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