efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation

Move the x86 EFI earlyprintk implementation to a shared location under
drivers/firmware and tweak it slightly so we can expose it as an earlycon
implementation (which is generic) rather than earlyprintk (which is only
implemented for a few architectures)

This also involves switching to write-combine mappings by default (which
is required on ARM since device mappings lack memory semantics, and so
memcpy/memset may not be used on them), and adding support for shared
memory framebuffers on cache coherent non-x86 systems (which do not
tolerate mismatched attributes).

Note that 32-bit ARM does not populate its struct screen_info early
enough for earlycon=efifb to work, so it is disabled there.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Alexander Graf <agraf@suse.de>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Jeffrey Hugo <jhugo@codeaurora.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Jones <pjones@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20190202094119.13230-10-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Author: Ard Biesheuvel

Documentation/admin-guide/kernel-parameters.txt

@@ -1073,9 +1073,15 @@
 			specified address. The serial port must already be
 			setup and configured. Options are not yet supported.
 
+		efifb,[options]
+			Start an early, unaccelerated console on the EFI
+			memory mapped framebuffer (if available). On cache
+			coherent non-x86 systems that use system memory for
+			the framebuffer, pass the 'ram' option so that it is
+			mapped with the correct attributes.
+
 	earlyprintk=	[X86,SH,ARM,M68k,S390]
 			earlyprintk=vga
-			earlyprintk=efi
 			earlyprintk=sclp
 			earlyprintk=xen
 			earlyprintk=serial[,ttySn[,baudrate]]

arch/x86/Kconfig.debug

@@ -40,16 +40,6 @@ config EARLY_PRINTK_DBGP
 	  with klogd/syslogd or the X server. You should normally say 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 EARLY_PRINTK_USB_XDBC
 	bool "Early printk via the xHCI debug port"
 	depends on EARLY_PRINTK && PCI

arch/x86/include/asm/efi.h

@@ -170,7 +170,6 @@ static inline bool efi_runtime_supported(void)
 	return false;
 }
 
-extern struct console early_efi_console;
 extern void parse_efi_setup(u64 phys_addr, u32 data_len);
 
 extern void efifb_setup_from_dmi(struct screen_info *si, const char *opt);

arch/x86/kernel/early_printk.c

@@ -388,10 +388,6 @@ static int __init setup_early_printk(char *buf)
 		if (!strncmp(buf, "xen", 3))
 			early_console_register(&xenboot_console, keep);
 #endif
-#ifdef CONFIG_EARLY_PRINTK_EFI
-		if (!strncmp(buf, "efi", 3))
-			early_console_register(&early_efi_console, keep);
-#endif
 #ifdef CONFIG_EARLY_PRINTK_USB_XDBC
 		if (!strncmp(buf, "xdbc", 4))
 			early_xdbc_parse_parameter(buf + 4);

arch/x86/platform/efi/Makefile

@@ -3,5 +3,4 @@ OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
 OBJECT_FILES_NON_STANDARD_efi_stub_$(BITS).o := y
 
 obj-$(CONFIG_EFI) 		+= quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
-obj-$(CONFIG_EARLY_PRINTK_EFI)	+= early_printk.o
 obj-$(CONFIG_EFI_MIXED)		+= efi_thunk_$(BITS).o

arch/x86/platform/efi/early_printk.c

@@ -198,3 +198,9 @@ config EFI_DEV_PATH_PARSER
 	bool
 	depends on ACPI
 	default n
+
+config EFI_EARLYCON
+	def_bool y
+	depends on SERIAL_EARLYCON && !ARM && !IA64
+	select FONT_SUPPORT
+	select ARCH_USE_MEMREMAP_PROT

drivers/firmware/efi/Kconfig

@@ -30,5 +30,6 @@ arm-obj-$(CONFIG_EFI)			:= arm-init.o arm-runtime.o
 obj-$(CONFIG_ARM)			+= $(arm-obj-y)
 obj-$(CONFIG_ARM64)			+= $(arm-obj-y)
 obj-$(CONFIG_EFI_CAPSULE_LOADER)	+= capsule-loader.o
+obj-$(CONFIG_EFI_EARLYCON)		+= earlycon.o
 obj-$(CONFIG_UEFI_CPER_ARM)		+= cper-arm.o
 obj-$(CONFIG_UEFI_CPER_X86)		+= cper-x86.o