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authorCatalin Marinas <catalin.marinas@arm.com>2012-10-23 14:55:08 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2013-01-22 17:51:01 +0000
commit2475ff9d2c6ea3bbfed55c4635426c371f9ad327 (patch)
treec705c9a55b2d9ea2d270b7002f568b6be0465ecd /arch/arm64/kernel/head.S
parentd6bafb9b821a3a5ddeb600a9fd015085760d818e (diff)
downloadlinux-linaro-stable-2475ff9d2c6ea3bbfed55c4635426c371f9ad327.tar.gz
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>
Diffstat (limited to 'arch/arm64/kernel/head.S')
-rw-r--r--arch/arm64/kernel/head.S12
1 files changed, 10 insertions, 2 deletions
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 368ad1f7c36c..0a0a49756826 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -82,10 +82,8 @@
#ifdef CONFIG_ARM64_64K_PAGES
#define MM_MMUFLAGS PTE_ATTRINDX(MT_NORMAL) | PTE_FLAGS
-#define IO_MMUFLAGS PTE_ATTRINDX(MT_DEVICE_nGnRE) | PTE_XN | PTE_FLAGS
#else
#define MM_MMUFLAGS PMD_ATTRINDX(MT_NORMAL) | PMD_FLAGS
-#define IO_MMUFLAGS PMD_ATTRINDX(MT_DEVICE_nGnRE) | PMD_SECT_XN | PMD_FLAGS
#endif
/*
@@ -368,6 +366,7 @@ ENDPROC(__calc_phys_offset)
* - identity mapping to enable the MMU (low address, TTBR0)
* - first few MB of the kernel linear mapping to jump to once the MMU has
* been enabled, including the FDT blob (TTBR1)
+ * - UART mapping if CONFIG_EARLY_PRINTK is enabled (TTBR1)
*/
__create_page_tables:
pgtbl x25, x26, x24 // idmap_pg_dir and swapper_pg_dir addresses
@@ -420,6 +419,15 @@ __create_page_tables:
sub x6, x6, #1 // inclusive range
create_block_map x0, x7, x3, x5, x6
1:
+#ifdef CONFIG_EARLY_PRINTK
+ /*
+ * Create the pgd entry for the UART mapping. The full mapping is done
+ * later based earlyprintk kernel parameter.
+ */
+ ldr x5, =EARLYCON_IOBASE // UART virtual address
+ add x0, x26, #2 * PAGE_SIZE // section table address
+ create_pgd_entry x26, x0, x5, x6, x7
+#endif
ret
ENDPROC(__create_page_tables)
.ltorg