x86/efi: Add EFI framebuffer earlyprintk support

It's incredibly difficult to diagnose early EFI boot issues without
special hardware because earlyprintk=vga doesn't work on EFI systems.

Add support for writing to the EFI framebuffer, via earlyprintk=efi,
which will actually give users a chance of providing debug output.

Cc: H. Peter Anvin <hpa@zytor.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Jones <pjones@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

Documentation/kernel-parameters.txt

@@ -792,6 +792,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 	earlyprintk=	[X86,SH,BLACKFIN,ARM]
 			earlyprintk=vga
+			earlyprintk=efi
 			earlyprintk=xen
 			earlyprintk=serial[,ttySn[,baudrate]]
 			earlyprintk=serial[,0x...[,baudrate]]
@@ -805,7 +806,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			Append ",keep" to not disable it when the real console
 			takes over.
 
-			Only vga or serial or usb debug port at a time.
+			Only one of vga, efi, serial, or usb debug port can
+			be used at a time.
 
 			Currently only ttyS0 and ttyS1 may be specified by
 			name.  Other I/O ports may be explicitly specified
@@ -819,8 +821,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			Interaction with the standard serial driver is not
 			very good.
 
-			The VGA output is eventually overwritten by the real
-			console.
+			The VGA and EFI output is eventually overwritten by
+			the real console.
 
 			The xen output can only be used by Xen PV guests.
 

arch/x86/Kconfig.debug

@@ -59,6 +59,16 @@ config EARLY_PRINTK_DBGP
 	  with klogd/syslogd or the X server. You should normally N here,
 	  unless you want to debug such a crash. You need usb debug device.
 
+config EARLY_PRINTK_EFI
+	bool "Early printk via the EFI framebuffer"
+	depends on EFI && EARLY_PRINTK
+	select FONT_SUPPORT
+	---help---
+	  Write kernel log output directly into the EFI framebuffer.
+
+	  This is useful for kernel debugging when your machine crashes very
+	  early before the console code is initialized.
+
 config X86_PTDUMP
 	bool "Export kernel pagetable layout to userspace via debugfs"
 	depends on DEBUG_KERNEL

arch/x86/include/asm/efi.h

@@ -109,6 +109,8 @@ static inline bool efi_is_native(void)
 	return IS_ENABLED(CONFIG_X86_64) == efi_enabled(EFI_64BIT);
 }
 
+extern struct console early_efi_console;
+
 #else
 /*
  * IF EFI is not configured, have the EFI calls return -ENOSYS.

arch/x86/kernel/early_printk.c

@@ -17,6 +17,8 @@
 #include <asm/mrst.h>
 #include <asm/pgtable.h>
 #include <linux/usb/ehci_def.h>
+#include <linux/efi.h>
+#include <asm/efi.h>
 
 /* Simple VGA output */
 #define VGABASE		(__ISA_IO_base + 0xb8000)
@@ -234,6 +236,11 @@ static int __init setup_early_printk(char *buf)
 			early_console_register(&early_hsu_console, keep);
 		}
 #endif
+#ifdef CONFIG_EARLY_PRINTK_EFI
+		if (!strncmp(buf, "efi", 3))
+			early_console_register(&early_efi_console, keep);
+#endif
+
 		buf++;
 	}
 	return 0;

arch/x86/platform/efi/Makefile

@@ -1,2 +1,3 @@
 obj-$(CONFIG_EFI) 		+= efi.o efi_$(BITS).o efi_stub_$(BITS).o
 obj-$(CONFIG_ACPI_BGRT) += efi-bgrt.o
+obj-$(CONFIG_EARLY_PRINTK_EFI)	+= early_printk.o

arch/x86/platform/efi/early_printk.c

@@ -0,0 +1,191 @@
+/*
+ * Copyright (C) 2013 Intel Corporation; author Matt Fleming
+ *
+ *  This file is part of the Linux kernel, and is made available under
+ *  the terms of the GNU General Public License version 2.
+ */
+
+#include <linux/console.h>
+#include <linux/efi.h>
+#include <linux/font.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <asm/setup.h>
+
+static const struct font_desc *font;
+static u32 efi_x, efi_y;
+
+static __init void early_efi_clear_scanline(unsigned int y)
+{
+	unsigned long base, *dst;
+	u16 len;
+
+	base = boot_params.screen_info.lfb_base;
+	len = boot_params.screen_info.lfb_linelength;
+
+	dst = early_ioremap(base + y*len, len);
+	if (!dst)
+		return;
+
+	memset(dst, 0, len);
+	early_iounmap(dst, len);
+}
+
+static __init void early_efi_scroll_up(void)
+{
+	unsigned long base, *dst, *src;
+	u16 len;
+	u32 i, height;
+
+	base = boot_params.screen_info.lfb_base;
+	len = boot_params.screen_info.lfb_linelength;
+	height = boot_params.screen_info.lfb_height;
+
+	for (i = 0; i < height - font->height; i++) {
+		dst = early_ioremap(base + i*len, len);
+		if (!dst)
+			return;
+
+		src = early_ioremap(base + (i + font->height) * len, len);
+		if (!src) {
+			early_iounmap(dst, len);
+			return;
+		}
+
+		memmove(dst, src, len);
+
+		early_iounmap(src, len);
+		early_iounmap(dst, len);
+	}
+}
+
+static void early_efi_write_char(u32 *dst, unsigned char c, unsigned int h)
+{
+	const u32 color_black = 0x00000000;
+	const u32 color_white = 0x00ffffff;
+	const u8 *src;
+	u8 s8;
+	int m;
+
+	src = font->data + c * font->height;
+	s8 = *(src + h);
+
+	for (m = 0; m < 8; m++) {
+		if ((s8 >> (7 - m)) & 1)
+			*dst = color_white;
+		else
+			*dst = color_black;
+		dst++;
+	}
+}
+
+static __init void
+early_efi_write(struct console *con, const char *str, unsigned int num)
+{
+	struct screen_info *si;
+	unsigned long base;
+	unsigned int len;
+	const char *s;
+	void *dst;
+
+	base = boot_params.screen_info.lfb_base;
+	si = &boot_params.screen_info;
+	len = si->lfb_linelength;
+
+	while (num) {
+		unsigned int linemax;
+		unsigned int h, count = 0;
+
+		for (s = str; *s && *s != '\n'; s++) {
+			if (count == num)
+				break;
+			count++;
+		}
+
+		linemax = (si->lfb_width - efi_x) / font->width;
+		if (count > linemax)
+			count = linemax;
+
+		for (h = 0; h < font->height; h++) {
+			unsigned int n, x;
+
+			dst = early_ioremap(base + (efi_y + h) * len, len);
+			if (!dst)
+				return;
+
+			s = str;
+			n = count;
+			x = efi_x;
+
+			while (n-- > 0) {
+				early_efi_write_char(dst + x*4, *s, h);
+				x += font->width;
+				s++;
+			}
+
+			early_iounmap(dst, len);
+		}
+
+		num -= count;
+		efi_x += count * font->width;
+		str += count;
+
+		if (num > 0 && *s == '\n') {
+			efi_x = 0;
+			efi_y += font->height;
+			str++;
+			num--;
+		}
+
+		if (efi_x >= si->lfb_width) {
+			efi_x = 0;
+			efi_y += font->height;
+		}
+
+		if (efi_y + font->height >= si->lfb_height) {
+			u32 i;
+
+			efi_y -= font->height;
+			early_efi_scroll_up();
+
+			for (i = 0; i < font->height; i++)
+				early_efi_clear_scanline(efi_y + i);
+		}
+	}
+}
+
+static __init int early_efi_setup(struct console *con, char *options)
+{
+	struct screen_info *si;
+	u16 xres, yres;
+	u32 i;
+
+	si = &boot_params.screen_info;
+	xres = si->lfb_width;
+	yres = si->lfb_height;
+
+	/*
+	 * early_efi_write_char() implicitly assumes a framebuffer with
+	 * 32-bits per pixel.
+	 */
+	if (si->lfb_depth != 32)
+		return -ENODEV;
+
+	font = get_default_font(xres, yres, -1, -1);
+	if (!font)
+		return -ENODEV;
+
+	efi_y = rounddown(yres, font->height) - font->height;
+	for (i = 0; i < (yres - efi_y) / font->height; i++)
+		early_efi_scroll_up();
+
+	return 0;
+}
+
+struct console early_efi_console = {
+	.name =		"earlyefi",
+	.write =	early_efi_write,
+	.setup =	early_efi_setup,
+	.flags =	CON_PRINTBUFFER,
+	.index =	-1,
+};