[ARM] 4423/1: add ATAGS support
Examines the ATAGS pointer (r2) at boot, and interprets
a nonzero value as a reference to an ATAGS structure. A
suitable ATAGS structure replaces the kernel's command line.
Signed-off-by: Bill Gatliff <bgat@billgatliff.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index a52da0d..024a9cf 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -20,7 +20,8 @@
.long _end @ r7
.long processor_id @ r4
.long __machine_arch_type @ r5
- .long cr_alignment @ r6
+ .long __atags_pointer @ r6
+ .long cr_alignment @ r7
.long init_thread_union + THREAD_START_SP @ sp
/*
@@ -29,6 +30,7 @@
*
* r0 = cp#15 control register
* r1 = machine ID
+ * r2 = atags pointer
* r9 = processor ID
*/
.type __mmap_switched, %function
@@ -47,11 +49,12 @@
strcc fp, [r6],#4
bcc 1b
- ldmia r3, {r4, r5, r6, sp}
+ ldmia r3, {r4, r5, r6, r7, sp}
str r9, [r4] @ Save processor ID
str r1, [r5] @ Save machine type
+ str r2, [r6] @ Save atags pointer
bic r4, r0, #CR_A @ Clear 'A' bit
- stmia r6, {r0, r4} @ Save control register values
+ stmia r7, {r0, r4} @ Save control register values
b start_kernel
/*
@@ -215,3 +218,34 @@
bl __lookup_machine_type
mov r0, r5
ldmfd sp!, {r4 - r6, pc}
+
+/* Determine validity of the r2 atags pointer. The heuristic requires
+ * that the pointer be aligned, in the first 16k of physical RAM and
+ * that the ATAG_CORE marker is first and present. Future revisions
+ * of this function may be more lenient with the physical address and
+ * may also be able to move the ATAGS block if necessary.
+ *
+ * r8 = machinfo
+ *
+ * Returns:
+ * r2 either valid atags pointer, or zero
+ * r5, r6 corrupted
+ */
+
+ .type __vet_atags, %function
+__vet_atags:
+ tst r2, #0x3 @ aligned?
+ bne 1f
+
+ ldr r5, [r2, #0] @ is first tag ATAG_CORE?
+ subs r5, r5, #ATAG_CORE_SIZE
+ bne 1f
+ ldr r5, [r2, #4]
+ ldr r6, =ATAG_CORE
+ cmp r5, r6
+ bne 1f
+
+ mov pc, lr @ atag pointer is ok
+
+1: mov r2, #0
+ mov pc, lr