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    SubjectRe: 2.6.17-rc1-mm1
    "Luck, Tony" <tony.luck@intel.com> wrote:
    >
    > On Wed, Apr 05, 2006 at 10:15:34AM -0600, Bjorn Helgaas wrote:
    > > Huh. Intel firmware used to just not mention the VGA framebuffer
    > > (0xa0000-0xc0000) at all in the EFI memory map. I think that was
    > > clearly a bug. So maybe they fixed that by marking it WB (and
    > > hopefully UC as well).
    >
    > Nope ... not fixed (at least not in the f/w that I'm running). The
    > VGA buffer is still simply not mentioned in the EFI memory map.
    >
    > The problem looks to come from this code in vgacon.c:
    >
    > vga_vram_base = VGA_MAP_MEM(vga_vram_base);
    > vga_vram_end = VGA_MAP_MEM(vga_vram_end);
    > vga_vram_size = vga_vram_end - vga_vram_base;
    >
    > vga_vram_base is 0xb8000, and this call gets a UC return of
    > c0000000000b8000. But vga_vram_end is 0xc0000 ... which is
    > the address of the start of a block of memory that is both
    > WB and UC capable.

    OK, so it's really an off-by-one error.

    > So ioremap() gives us e0000000000c0000
    > (which means that vga_vram_size is 2000000000008000, surely
    > the biggest, baddest video card in the history of the world!).
    >
    > Perhaps the right fix is to subtract 1 from vga_vram_end and pass
    > that into VGA_MAP_MEM(), and then add the 1 byte back when computing
    > the size? But I don't know whether that might do something bad on
    > some other architecture that uses vgacon.c. If this is not
    > acceptable, then we can fall back and use the Nanhai/Bjorn fix
    > of using ioremap_nocache().
    >
    > Signed-off-by: Tony Luck <tony.luck@intel.com>
    >
    > ---
    >
    > diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
    > index d5a04b6..4ca9877 100644
    > --- a/drivers/video/console/vgacon.c
    > +++ b/drivers/video/console/vgacon.c
    > @@ -484,8 +484,8 @@ #endif
    > }
    >
    > vga_vram_base = VGA_MAP_MEM(vga_vram_base);
    > - vga_vram_end = VGA_MAP_MEM(vga_vram_end);
    > - vga_vram_size = vga_vram_end - vga_vram_base;
    > + vga_vram_end = VGA_MAP_MEM(vga_vram_end - 1);
    > + vga_vram_size = vga_vram_end - vga_vram_base + 1;
    >
    > /*
    > * Find out if there is a graphics card present.

    Looks like the correct fix to me.

    Tony (D), can you think of any problems with that approach?
    -
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