[PATCH 2/3] ARM: Define kernel physical section start and end

[Linus Walleij]

When we are mapping the initial sections in head.S we
know very well where the start and end of the kernel image
in physical memory is placed. Later on it gets hard
to determine this.

Save the information into two variables named
kernel_sec_start and kernel_sec_end for convenience
for later work involving the physical start and end
of the kernel. These variables are section-aligned
corresponding to the early section mappings set up
in head.S.

Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
 arch/arm/include/asm/memory.h |  7 +++++++
 arch/arm/kernel/head.S        | 27 ++++++++++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index a5f1d1826a98..ca213d7d095f 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -158,6 +158,13 @@ extern unsigned long vectors_base;
 
 #ifndef __ASSEMBLY__
 
+/*
+ * Physical start and end address of the kernel sections. These addresses are
+ * 2MB-aligned to match the section mappings placed over the kernel.
+ */
+extern phys_addr_t kernel_sec_start;
+extern phys_addr_t kernel_sec_end;
+
 /*
  * Physical vs virtual RAM address space conversion.  These are
  * private definitions which should NOT be used outside memory.h
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 4e2daaa7636a..9eb0b4dbcc12 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -47,6 +47,20 @@
 	.globl	swapper_pg_dir
 	.equ	swapper_pg_dir, KERNEL_RAM_VADDR - PG_DIR_SIZE
 
+	/*
+	 * This needs to be assigned at runtime when the linker symbols are
+	 * resolved.
+	 */
+	.pushsection .data
+	.align	2
+	.globl	kernel_sec_start
+	.globl	kernel_sec_end
+kernel_sec_start:
+	.long	0
+kernel_sec_end:
+	.long	0
+	.popsection
+
 	.macro	pgtbl, rd, phys
 	add	\rd, \phys, #TEXT_OFFSET
 	sub	\rd, \rd, #PG_DIR_SIZE
@@ -229,16 +243,23 @@ __create_page_tables:
 	blo	1b
 
 	/*
-	 * Map our RAM from the start to the end of the kernel .bss section.
+	 * The main matter: map in the kernel using section mappings, and
+	 * set two variables to indicate the physical start and end of the
+	 * kernel.
 	 */
-	add	r0, r4, #PAGE_OFFSET >> (SECTION_SHIFT - PMD_ORDER)
+	add	r0, r4, #KERNEL_OFFSET >> (SECTION_SHIFT - PMD_ORDER)
 	ldr	r6, =(_end - 1)
-	orr	r3, r8, r7
+	adr_l	r5, kernel_sec_start		@ _pa(kernel_sec_start)
+	str	r8, [r5]			@ Save physical start of kernel
+	orr	r3, r8, r7			@ Add the MMU flags
 	add	r6, r4, r6, lsr #(SECTION_SHIFT - PMD_ORDER)
 1:	str	r3, [r0], #1 << PMD_ORDER
 	add	r3, r3, #1 << SECTION_SHIFT
 	cmp	r0, r6
 	bls	1b
+	eor	r3, r3, r7			@ Remove the MMU flags
+	adr_l	r5, kernel_sec_end		@ _pa(kernel_sec_end)
+	str	r3, [r5]			@ Save physical end of kernel
 
 #ifdef CONFIG_XIP_KERNEL
 	/*
-- 
2.31.1