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    SubjectRe: [PATCH 2.4.29-pre1] radeonfb: don't try to ioreamp the entire VRAM [was: Re: [Linux-fbdev-devel] why does radeonfb work fine in 2.6, but not in 2.4.29-pre1?]
    On Wed, 1 Dec 2004, Kronos wrote:
    > Il Wed, Dec 01, 2004 at 05:25:52PM +0100, Geert Uytterhoeven ha scritto:
    > > > Make fb layer aware of the difference between the ioremap()'ed VRAM and
    > > > total available VRAM.
    > > > smem_len in struct fb_fix_screeninfo still contains the amount of
    > > > physical VRAM (reported to userspace via FBIOGET_FSCREENINFO ioctl) and
    > > > the new field mapped_vram contains the amount of VRAM actually
    > > > ioremap()'ed by drivers (used in read/write/mmap operations).
    > > > Since there was unused padding at the end of struct fb_fix_screeninfo
    > > > binary compatibility with userspace utilities is retained.
    > > > If mapped_vram is not set it's assumed that the entire framebuffer is
    > > > mapped, thus other drivers are unaffected by this patch.
    > > >
    > > > The patch has been tested by Jurriaan <thunder7@xs4all.nl>.
    > > >
    > > > Signed-off-by: Luca Tettamanti <kronos@people.it>
    > > >
    > > > --- a/include/linux/fb.h 2004-11-30 18:30:08.000000000 +0100
    > > > +++ b/include/linux/fb.h 2004-11-30 18:33:00.000000000 +0100
    > > > @@ -126,7 +126,8 @@
    > > > /* (physical address) */
    > > > __u32 mmio_len; /* Length of Memory Mapped I/O */
    > > > __u32 accel; /* Type of acceleration available */
    > > > - __u16 reserved[3]; /* Reserved for future compatibility */
    > > > + __u32 mapped_vram; /* Amount of ioremap()'ed VRAM */
    > > > + __u16 reserved[1]; /* Reserved for future compatibility */
    > > > };
    > >
    > > I don't really like this patch. mapped_vram doesn't matter for user space at
    > > all, so it does not belong to fb_fix_screeninfo.
    >
    > Hmm, it looked sensible to me since it's the max amount of data that
    > userspace can read (or write) from /dev/fb%d.

    That's not really a user space limitation, but a kernel `bug'.

    I.e. it could be solved in the kernel if larger ioremap()s would be allowed, or
    if some sliding window mapping would be used. User space shouldn't need to know
    about this.

    > Putting mapped_vram in fb_info would be acceptable?

    That would make sure this stays in-kernel, but my other reasoning stays the
    same: it's some kind of kernel bug.

    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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