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