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    SubjectRe: [PATCH] Make bootsector stub 16-bit-only (i386)
    On Tue, 8 May 2007 20:32:32 +0200
    Alexander van Heukelum <heukelum@mailshack.com> wrote:

    > On Tue, May 08, 2007 at 03:28:17AM -0700, Andrew Morton wrote:
    > > On Sat, 5 May 2007 12:44:52 +0200 Alexander van Heukelum <heukelum@mailshack.com> wrote:
    > > > --- a/arch/i386/boot/bootsect.S
    > > > +++ b/arch/i386/boot/bootsect.S
    > > > @@ -44,7 +44,7 @@ #endif
    > > > _start:
    > > >
    > > > # Normalize the start address
    > > > - jmpl $BOOTSEG, $start2
    > > > + jmpw $BOOTSEG, $start2
    > >
    > > Sigh, another blow struck in the ongoing struggle between my Vaio and the
    > > rest of the world.
    > >
    > > Stone-cold black-screen lockup immediately upon boot.
    > >
    > > Stock FC5 install, config at
    > > http://userweb.kernel.org/~akpm/config-sony.txt
    >
    > Sigh... sounds impossible.
    >
    > I assume this is repeatable?

    100%

    > And this patch changes behaviour?

    Yup.

    > What do you mean by immediate?

    Basically the last thing I see is grub.

    > Before or after decompression?

    Not sure - things happen pretty quickly and I suspect info is getting lost
    when the display is changing modes.

    > Fishy... As Andi and Peter have mentioned, this code is not executed.
    > There is only one user of the same memory area this early... video.S
    > uses it to store some collected data, but as far as I can see only the
    > 'CONFIG_VIDEO_RETAIN' code also reads it back. If it happens before
    > decompression, could you see if changing
    > #define CONFIG_VIDEO_RETAIN -> #undef CONFIG_VIDEO_RETAIN
    > in arch/i386/boot/video.S changes anything?
    >
    > Do you select a non-standard textmode?

    yep.

    > Does vga=ask show up?

    no.

    > *looks around some*
    >
    > Oh! A padding hole in a struct! That could be a problem. If the freeze
    > is after decompression, could you test if this makes it work again?

    I shall try that later in the day.

    >
    > ---
    >
    > Commit 89ec4c238e7a3d7e660291f3f1a8181381baad77 introduced a discrepancy
    > between the struct screen_info which is used by the C code, and the
    > PARAM_* offsets which are used in the real-mode kernel. This is an
    > attempt to rectify the situation, but I have no way to test it.
    >
    > Signed-off-by: Alexander van Heukelum <heukelum@mailshack.com>
    >
    > ---
    >
    > diff --git a/arch/i386/boot/bootsect.S b/arch/i386/boot/bootsect.S
    > diff --git a/arch/i386/boot/video.S b/arch/i386/boot/video.S
    > index 8143c95..8e404cb 100644
    > --- a/arch/i386/boot/video.S
    > +++ b/arch/i386/boot/video.S
    > @@ -95,7 +95,8 @@ #define PARAM_VESAPM_SEG 0x2e
    > #define PARAM_VESAPM_OFF 0x30
    > #define PARAM_LFB_PAGES 0x32
    > #define PARAM_VESA_ATTRIB 0x34
    > -#define PARAM_CAPABILITIES 0x36
    > +#define PARAM_VESA_PAD 0x36
    > +#define PARAM_CAPABILITIES 0x38
    >
    > /* Define DO_STORE according to CONFIG_VIDEO_RETAIN */
    > #ifdef CONFIG_VIDEO_RETAIN
    > diff --git a/include/linux/screen_info.h b/include/linux/screen_info.h
    > index b02308e..0a2e892 100644
    > --- a/include/linux/screen_info.h
    > +++ b/include/linux/screen_info.h
    > @@ -41,8 +41,8 @@ struct screen_info {
    > u16 vesapm_off; /* 0x30 */
    > u16 pages; /* 0x32 */
    > u16 vesa_attributes; /* 0x34 */
    > - u32 capabilities; /* 0x36 */
    > - /* 0x3a -- 0x3b reserved for future expansion */
    > + u16 vesa_pad; /* 0x36 */
    > + u32 capabilities; /* 0x38 */
    > /* 0x3c -- 0x3f micro stack for relocatable kernels */
    > };
    >
    -
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