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authorH. Peter Anvin <hpa@zytor.com>2007-07-18 03:16:10 +0400
committerH. Peter Anvin <hpa@zytor.com>2007-07-18 22:36:17 +0400
commit7ad37df02c529525c4ad19035359af89d2d2a5bd (patch)
treed747f8fce857c6498c88cfb7608d2d3c6425fa34 /arch
parent5593eaa854d0b23c3b270933a93b9b82946df729 (diff)
downloadlinux-7ad37df02c529525c4ad19035359af89d2d2a5bd.tar.xz
[x86 setup] VGA: Clear the Protect bit before setting the vertical height
If the user has asked for the vertical height registers to be recomputed by setting bit 15 in the video mode number, we do so without clearing the Protect bit in the Vertical Retrace Register before setting the Overflow register. As a result, if the VGA BIOS had set the Protect bit, the write to the Overflow register will be dropped, and bits [9:8] of the vertical height will be left unchanged. This is a bug imported from the assembly version of this code. It was pointed out by Etienne Lorrain. Cc: Etienne Lorrain <etienne_lorrain@yahoo.fr> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/i386/boot/video.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/i386/boot/video.c b/arch/i386/boot/video.c
index 027a2c90300b..958130ef0042 100644
--- a/arch/i386/boot/video.c
+++ b/arch/i386/boot/video.c
@@ -195,7 +195,7 @@ static void vga_recalc_vertical(void)
{
unsigned int font_size, rows;
u16 crtc;
- u8 ov;
+ u8 pt, ov;
set_fs(0);
font_size = rdfs8(0x485); /* BIOS: font size (pixels) */
@@ -206,7 +206,12 @@ static void vga_recalc_vertical(void)
crtc = vga_crtc();
+ pt = in_idx(crtc, 0x11);
+ pt &= ~0x80; /* Unlock CR0-7 */
+ out_idx(pt, crtc, 0x11);
+
out_idx((u8)rows, crtc, 0x12); /* Lower height register */
+
ov = in_idx(crtc, 0x07); /* Overflow register */
ov &= 0xbd;
ov |= (rows >> (8-1)) & 0x02;