Re: [Linux-fbdev-devel] New API

[Geert U. <ge...@li...>]

On Wed, 14 Nov 2001, James Simmons wrote:
> Hi folks. I finally hammered a newer api for framebuffer devices. I
> adapted skeletonfb.c to show it off. Feedback welcomed.

Good news!

>     /*
>      *  If your driver supports multiple boards, you should make these
>      *  arrays, or allocate them dynamically (using kmalloc()).
>      */

Perhaps make it more clear that this applies to all 3 (4?) variables below

> static struct fb_info info;
>     /*
>      * This represents the default state of the hardware.
>      */
> static struct xxx_par __initdata current_par;
>
> static u32 xxxfb_pseudo_palette[17];
> static int inverse = 0;

> /**
>  *      xxxfb_check_var - REQUIRED function. Validates a var passed in.

Is this function really required? Imagine a graphics card with a fixed
resolution (e.g. old Sun3 bwtwo), or vesafb/offb.

If it's NULL, you cannot change var, and upper layer can check that an
identical var was passed (using memcmp()).

>  *  	xxxfb_setcolreg - REQUIRED function. Sets a color register.

Is this function really required? Imagine static pseudocolor (fixed palette)
hardware.

>     /* Directcolor:
>      *   var->{color}.offset contains start of bitfield
>      *   var->{color}.length contains length of bitfield
>      *   {hardwarespecific} contains width of DAC
>      *   cmap[X] is programmed to (X << red.offset) | (X << green.offset) | (X << blue.offset)
>      *   DAC[X] is programmed to (red, green, blue)

s/DAC/RAMDAC/

>      *
>      * Pseudocolor:
>      *    uses offset = 0 && length = DAC register width.
>      *    var->{color}.offset is 0
>      *    var->{color}.length contains widht of DAC
>      *    cmap is not used
>      *    DAC[X] is programmed to (red, green, blue)

s/DAC/RAMDAC/

>      * Truecolor:
>      *    does not use DAC.
>      *    var->{color}.offset contains start of bitfield
>      *    var->{color}.length contains length of bitfield
>      *    cmap is programmed to (red << red.offset) | (green << green.offset) |
>      *                      (blue << blue.offset) | (transp << transp.offset)
>      *    DAC does not exist

s/DAC/RAMDAC/

Truecolor does have a DAC (even 3 of them :-), but no RAMDAC.

>     /* Truecolor has hardware independent palette */
>     if (info->fix.visual == FB_VISUAL_TRUECOLOR) {
>        u32 v;
>
>        if (regno >= 16)
>            return 1;
>
>        v = (red << info->var.red.offset) |
>            (green << info->var.green.offset) |
>            (blue << info->var.blue.offset) |
>            (transp << info->var.transp.offset);
>        if (info->var.bits_per_pixel == 16)
>            ((u16*)(info->pseudo_palette))[regno] = v;
>        else
>            ((u32*)(info->pseudo_palette))[regno] = v;
>        return 0;

What about info->var.bits_per_pixel == 8? Some handhelds are RGB332 truecolor.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@li...

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