kexec: fix i386 EFI boot using efifb

Problem:
	kexec fails under i386 EFI boot for hardware that does not
have a VGA bios or PC bios present. The EFI bootloader properly set
the initial screen_info boot params but kexec assumes an
orig_video_isVGA type of 1. This causes the kexec'd kernel assume the
presence of both VGA bios and normal PC BIOS and starts probing which
then panics somewhere I can't see because I have no console output
nor serial ports.

Solution:
	For EFI, efifb is a linear VGA framebuffer and can handle the
kexec kernel switch, kexec just has to setup the kernel boot params
properly. The below patch fixes this issue and allow a i386 EFI
booted kernel with no VGA bios/PC bios to kexec to another kernel.

Questions:
	Why is kexec assuming i386 x86 == VGA bios in the first
place. The existing kernel has a perfectly good screen_info stucture
that is an exported symbol by the kernel and could be accessed by
kexec. Since kexec is just pretending to be a boot loader, why does
it ignore information that the real bootloader (which knows a lot
more about the hardware) has passed? The below patch just hacks in a
trap for efifb and will fail in the future as other x86 hardware
without VGA bios/PC bios become available.

Signed-off-by: Scott D Davilla <davilla@4pi.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 9 insertions, 3 deletions

diff --git a/kexec/arch/i386/x86-linux-setup.c b/kexec/arch/i386/x86-linux-setup.c
index 68234fa..97480fd 100644
--- a/kexec/arch/i386/x86-linux-setup.c
+++ b/kexec/arch/i386/x86-linux-setup.c
@@ -104,7 +104,6 @@ int setup_linux_vesafb(struct x86_linux_param_header *real_mode)
 {
 	struct fb_fix_screeninfo fix;
 	struct fb_var_screeninfo var;
-	static char *magic = "VESA VGA";
 	int fd;
 
 	fd = open("/dev/fb0", O_RDONLY);
@@ -115,11 +114,18 @@ int setup_linux_vesafb(struct x86_linux_param_header *real_mode)
 		goto out;
 	if (-1 == ioctl(fd, FBIOGET_VSCREENINFO, &var))
 		goto out;
-	if (0 != strcmp(fix.id, magic))
+	if (0 == strcmp(fix.id, "VESA VGA")) {
+		/* VIDEO_TYPE_VLFB */
+		real_mode->orig_video_isVGA = 0x23;
+	} else if (0 == strcmp(fix.id, "EFI VGA")) {
+		/* VIDEO_TYPE_EFI */
+		real_mode->orig_video_isVGA = 0x70;
+	} else {
+		/* cannot handle and other types */
 		goto out;
+	}
 	close(fd);
 
-	real_mode->orig_video_isVGA = 0x23 /* VIDEO_TYPE_VLFB */;
 	real_mode->lfb_width      = var.xres;
 	real_mode->lfb_height     = var.yres;
 	real_mode->lfb_depth      = var.bits_per_pixel;