On Tue, 22 Apr 2008, Benjamin Herrenschmidt wrote:

We currently have a problem with those two members of struct
fb_fix_screeninfo. The struct contains an "unsigned long" which means
that:

- 64 bits kernels with 32 bits userspace can't pass a complete address
- 32 bits machines with 64 bits resource_size_t can't pass a complete
address
- The structure isn't even properly padded to be 32/64 bits neutral in
the first place.

We could define new versions of the struct with new get/set ioctls,
or we could try to just deprecate those fields. What do you guys think ?

As userspace doesn't really need those fields[1], we can easily deprecate them.

If we do the later, we need another way to convey the informations.

For smem, I'm not sure it's very useful, we should just be able to mmap
the fbdev. The problem is more with mmio_start.

Thus the idea that we could do something to allow mmap'ing mmio via
mmap of /dev/fb via some specific offset... what do you think ?

That's exactly what drivers/video/fbmem.c:fb_mmap() does[2].

But fb_mmap() does need the correct (resource_size_t) information.
That can be done by changing the offending fields in the kernel variant of
fb_fix_screeninfo to resource_size_t.

The user variant of fb_fix_screeninfo would stay the same, and only the
FBIOGET_FSCREENINFO case in drivers/video/fbmem.c:fb_ioctl() has to be
changed to convert from the kernel to the user variant.

Or we can just do a fb_fix_screeninfo2, with proper padding and u64
addresses, replace the kernel one with that, have translators for the
old ioctl's, and new ioctl's.

I don't think the new ioctls are needed.

[1] Except when it wants to mmap /dev/mem using this info, but that can
    be done using [2].

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@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

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