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

From: Geert Uytterhoeven
Date: Thu Jul 28 2005 - 16:44:41 EST

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.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at