arm64: Add simple earlyprintk support

This patch adds support for "earlyprintk=" parameter on the kernel
command line. The format is:

  earlyprintk=<name>[,<addr>][,<options>]

where <name> is the name of the (UART) device, e.g. "pl011", <addr> is
the I/O address. The <options> aren't currently used.

The mapping of the earlyprintk device is done very early during kernel
boot and there are restrictions on which functions it can call. A
special early_io_map() function is added which creates the mapping from
the pre-defined EARLY_IOBASE to the device I/O address passed via the
kernel parameter. The pgd entry corresponding to EARLY_IOBASE is
pre-populated in head.S during kernel boot.

Only PL011 is currently supported and it is assumed that the interface
is already initialised by the boot loader before the kernel is started.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

3 files changed, 5 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index d2f05a608274..57f12c991de2 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -230,6 +230,9 @@ extern void __iounmap(volatile void __iomem *addr);
 #define ioremap_wc(addr, size)          __ioremap((addr), (size), __pgprot(PROT_NORMAL_NC))
 #define iounmap                         __iounmap
 
+#define PROT_SECT_DEFAULT       (PMD_TYPE_SECT | PMD_SECT_AF)
+#define PROT_SECT_DEVICE_nGnRE  (PROT_SECT_DEFAULT | PTE_PXN | PTE_UXN | PMD_ATTRINDX(MT_DEVICE_nGnRE))
+
 #define ARCH_HAS_IOREMAP_WC
 #include <asm-generic/iomap.h>
 
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 1cac16a001cb..381f556b664e 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -43,6 +43,7 @@
 #define PAGE_OFFSET             UL(0xffffffc000000000)
 #define MODULES_END             (PAGE_OFFSET)
 #define MODULES_VADDR           (MODULES_END - SZ_64M)
+#define EARLYCON_IOBASE         (MODULES_VADDR - SZ_4M)
 #define VA_BITS                 (39)
 #define TASK_SIZE_64            (UL(1) << VA_BITS)
 
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index d4f7fd5b9e33..2494fc01896a 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -26,5 +26,6 @@ typedef struct {
 
 extern void paging_init(void);
 extern void setup_mm_for_reboot(void);
+extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
 
 #endif