[x86 setup] VGA: Clear the Protect bit before setting the vertical height (7ad37df0) · Commits · 戴 / test

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>

arch/i386/boot/video.c

+6 −1

Original line number	Original line	Diff line number	Diff line
	@@ -195,7 +195,7 @@ static void vga_recalc_vertical(void)
	{		{
	unsigned int font_size, rows;		unsigned int font_size, rows;
	u16 crtc;		u16 crtc;
	u8 ov;		u8 pt, ov;

	set_fs(0);		set_fs(0);
	font_size = rdfs8(0x485); /* BIOS: font size (pixels) */		font_size = rdfs8(0x485); /* BIOS: font size (pixels) */
	@@ -206,7 +206,12 @@ static void vga_recalc_vertical(void)

	crtc = vga_crtc();		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 */		out_idx((u8)rows, crtc, 0x12); /* Lower height register */

	ov = in_idx(crtc, 0x07); /* Overflow register */		ov = in_idx(crtc, 0x07); /* Overflow register */
	ov &= 0xbd;		ov &= 0xbd;
	ov \|= (rows >> (8-1)) & 0x02;		ov \|= (rows >> (8-1)) & 0x02;

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