[PATCH/RFC] fbdev: Add FOURCC-based format configuration API

[Geert Uytterhoeven]

On Thu, Jul 28, 2011 at 12:51, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>> As for struct fb_var_screeninfo fields to support switching to a FOURCC
>> mode, I also prefer an explicit dedicated flag to specify switching to it.
>> Even though using FOURCC doesn't fit under the notion of a videomode, using
>> one of .vmode bits is too tempting, so, I would actually take the plunge and
>> use FB_VMODE_FOURCC.
>
> Another option would be to consider any grayscale > 1 value as a FOURCC. I've
> briefly checked the in-tree drivers: they only assign grayscale with 0 or 1,
> and check whether grayscale is 0 or different than 0. If a userspace
> application only sets grayscale > 1 when talking to a driver that supports the
> FOURCC-based API, we could get rid of the flag.
>
> What can't be easily found out is whether existing applications set grayscale
> to a > 1 value. They would break when used with FOURCC-aware drivers if we
> consider any grayscale > 1 value as a FOURCC. Is that a risk we can take ?

I think we can. I'd expect applications to use either 1 or -1 (i.e.
all ones), both are
invalid FOURCC values.

Still, I prefer the nonstd way.
And limiting traditional nonstd values to the lowest 24 bits (there
are no in-tree
drivers using the highest 8 bits, right?).

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

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