[PATCH V4] ARM: implement debug_ll_io_init()

Stephen Warren swarren at wwwdotorg.org
Mon Oct 22 13:42:54 EDT 2012

From: Rob Herring <robherring2 at gmail.com>

When using DEBUG_LL, the UART's (or other HW's) registers are mapped
into early page tables based on the results of assembly macro addruart.
Later, when the page tables are replaced, the same virtual address must
remain valid. Historically, this has been ensured by using defines from
<mach/iomap.h> in both the implementation of addruart, and the machine's
.map_io() function. However, with the move to single zImage, we wish to
remove <mach/iomap.h>. To enable this, the macro addruart may be used
when constructing the late page tables too; addruart is exposed as a
C function debug_ll_addr(), and used to set up the required mapping in
debug_ll_io_init(), which may called on an opt-in basis from a machine's
.map_io() function.

Signed-off-by: Rob Herring <rob.herring at calxeda.com>
[swarren: Mask map.virtual with PAGE_MASK. Checked for NULL results from
 debug_ll_addr (e.g. when selected UART isn't valid). Fixed compile when
Signed-off-by: Stephen Warren <swarren at nvidia.com>
This patch is a dependency for the Tegra debug-macro.S rework. I assume it
should go into some arm-soc branch so that if others want to take advantage
of it this kernel cycle, they can.

v4: Fix DEBUG_SEMIHOSTING's debug_ll_addr to actually fill in the "out"
v3: New patch.
 arch/arm/include/asm/mach/map.h |    7 +++++++
 arch/arm/kernel/debug.S         |   14 ++++++++++++++
 arch/arm/mm/mmu.c               |   16 ++++++++++++++++
 3 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/arch/arm/include/asm/mach/map.h b/arch/arm/include/asm/mach/map.h
index 195ac2f..2fe141f 100644
--- a/arch/arm/include/asm/mach/map.h
+++ b/arch/arm/include/asm/mach/map.h
@@ -40,6 +40,13 @@ extern void iotable_init(struct map_desc *, int);
 extern void vm_reserve_area_early(unsigned long addr, unsigned long size,
 				  void *caller);
+extern void debug_ll_addr(unsigned long *paddr, unsigned long *vaddr);
+extern void debug_ll_io_init(void);
+static inline void debug_ll_io_init(void) {}
 struct mem_type;
 extern const struct mem_type *get_mem_type(unsigned int type);
diff --git a/arch/arm/kernel/debug.S b/arch/arm/kernel/debug.S
index 66f711b..6809200 100644
--- a/arch/arm/kernel/debug.S
+++ b/arch/arm/kernel/debug.S
@@ -100,6 +100,13 @@ ENTRY(printch)
 		b	1b
+		addruart r2, r3, ip
+		str	r2, [r0]
+		str	r3, [r1]
+		mov	pc, lr
@@ -119,4 +126,11 @@ ENTRY(printch)
 		mov	pc, lr
+		mov	r2, #0
+		str	r2, [r0]
+		str	r2, [r1]
+		mov	pc, lr
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 941dfb9..39719bb 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -876,6 +876,22 @@ static void __init pci_reserve_io(void)
 #define pci_reserve_io() do { } while (0)
+void __init debug_ll_io_init(void)
+	struct map_desc map;
+	debug_ll_addr(&map.pfn, &map.virtual);
+	if (!map.pfn || !map.virtual)
+		return;
+	map.pfn = __phys_to_pfn(map.pfn);
+	map.virtual &= PAGE_MASK;
+	map.length = PAGE_SIZE;
+	map.type = MT_DEVICE;
+	create_mapping(&map);
 static void * __initdata vmalloc_min =
 	(void *)(VMALLOC_END - (240 << 20) - VMALLOC_OFFSET);

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