Re: [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?]

Geert Uytterhoeven
2004-12-01T21:27:36Z

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