[ARM] 3809/3: get rid of 4 megabyte kernel image size limit

We currently have a hardcoded 4 megabyte uncompressed kernel image
size limit, which is easily exceeded by, for example, enabling some of
the various kernel debugging options.

When setting up the initial page tables (which is where this 4M limit
is hardcoded), it's actually relatively easy to find out the true size
of the uncompressed kernel image and create enough page table entries
for things to fit, so this patch makes it so.

In the decompressor, we also need to know the size of the uncompressed
kernel image, to figure out whether there is any chance that uncompressing
the kernel might overwrite the compressed kernel image stored elsewhere
in memory. We don't have that info at this boot stage, though, so we
approximate the size of the uncompressed kernel by taking the compressed
kernel image size and allowing for a maximum 4x expansion.
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/head.S

@@ -237,7 +237,8 @@ not_relocated:	mov	r0, #0
  */
 		cmp	r4, r2
 		bhs	wont_overwrite
-		add	r0, r4, #4096*1024	@ 4MB largest kernel size
+		sub	r3, sp, r5		@ > compressed kernel size
+		add	r0, r4, r3, lsl #2	@ allow for 4x expansion
 		cmp	r0, r5
 		bls	wont_overwrite
 

arch/arm/kernel/head.S

@@ -234,18 +234,18 @@ __create_page_tables:
 
 	/*
 	 * Now setup the pagetables for our kernel direct
-	 * mapped region.  We round TEXTADDR down to the
-	 * nearest megabyte boundary.  It is assumed that
-	 * the kernel fits within 4 contigous 1MB sections.
+	 * mapped region.
 	 */
 	add	r0, r4,  #(TEXTADDR & 0xff000000) >> 18	@ start of kernel
 	str	r3, [r0, #(TEXTADDR & 0x00f00000) >> 18]!
-	add	r3, r3, #1 << 20
-	str	r3, [r0, #4]!			@ KERNEL + 1MB
-	add	r3, r3, #1 << 20
-	str	r3, [r0, #4]!			@ KERNEL + 2MB
-	add	r3, r3, #1 << 20
-	str	r3, [r0, #4]			@ KERNEL + 3MB
+
+	ldr	r6, =(_end - PAGE_OFFSET - 1)	@ r6 = number of sections
+	mov	r6, r6, lsr #20			@ needed for kernel minus 1
+
+1:	add	r3, r3, #1 << 20
+	str	r3, [r0, #4]!
+	subs	r6, r6, #1
+	bgt	1b
 
 	/*
 	 * Then map first 1MB of ram in case it contains our boot params.