Problem with current fb_get_color_depth function

From: Joshua Kwan (joshk_at_triplehelix.org)
Date: 10/11/04

  • Next message: Aboo Valappil: "RE: how do you call userspace syscalls (e.g. sys_rename) from inside kernel" 
    Date:	Sun, 10 Oct 2004 15:59:03 -0700
To: adaplas@pol.net

    Hi Antonino, lists, etc.,

    I noticed that after 2.6.9-rc1 or so my framebuffer logo stopped
    appearing. Well, I dove into the fb layer code, noticed this change from
    you:

    int fb_get_color_depth(struct fb_info *info)
    {
        struct fb_var_screeninfo *var = &info->var;

        if (var->green.length == var->blue.length &&
            var->green.length == var->red.length &&
            !var->green.offset && !var->blue.offset &&
            !var->red.offset)
            return var->green.length;
        else
            return (var->green.length + var->red.length +
                var->blue.length);
    }

    That was interesting, because here's what radeonfb does:

            switch (var_to_depth(&v)) {
    [...]
                    case 16:
                            nom = 2;
                            den = 1;
                            v.red.offset = 11;
                            v.green.offset = 5;
                            v.blue.offset = 0;
                            v.red.length = 5;
                            v.green.length = 6;
                            v.blue.length = 5;
                            v.transp.offset = v.transp.length = 0;
                            break;
    [...]

    So somehow that first conditional was firing, although I'm not sure how,
    because a printk showed that the depth returned was 6. (fb_get_color_depth
    should have jumped to the return (R + G + B) part right after it noticed
    blue length was not equal to green length. Creepy.)

    Well, whatever. The 224-color logo was ignored. This is what I did to
    fix it:

    --- a/drivers/video/fbmem.c 2004/09/23 01:19:45 1.102
    +++ b/drivers/video/fbmem.c 2004/10/10 22:47:14
    @@ -65,10 +65,8 @@
     {
             struct fb_var_screeninfo *var = &info->var;
     
    - if (var->green.length == var->blue.length &&
    - var->green.length == var->red.length &&
    - !var->green.offset && !var->blue.offset &&
    - !var->red.offset)
    + /* If grayscale, all values will be equal */
    + if (var->grayscale)
                     return var->green.length;
             else
                     return (var->green.length + var->red.length +

    because on advice from Andrew Suffield and Matthew Garrett the first
    conditional was a roundabout way to check for grayscale displays, where
    you can't actually have 24 bits (8 + 8 + 8) of gray. So it is suitable
    to just return one of the values arbitrarily. But I noticed there was
    also a grayscale variable, so I substituted that for the conditional
    and my logo reappeared again :)

    So is radeonfb or fb_get_color_depth at fault here? Or was the logo
    never appropriate for my display in the first place? (Unlikely, the
    CLUT224 linux logo always displayed perfectly for me until now.)

    Thanks. 

    -- 
Joshua Kwan

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