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

From: Antonino A. Daplas
Date: Thu Jul 28 2005 - 17:30:58 EST

Jon Smirl wrote:
On 7/28/05, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> 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.

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