imx: fix exception vectors relocation in imx27

Commit 3ff46cc4 fixed exception vectors setting in
the general ARM case, by either copying the exception
and indirect vector tables to normal (0x00000000) or
high (0xFFFF0000) vectors address, or setting VBAR to
U-Boot's base if applicable.

i.MX27 SoC is ARM926E-JS, thus has only normal and
high options, but does not provide RAM at 0xFFFF0000
and has only ROM at 0x00000000; it is therefore not
possible to move or change its exception vectors.

Besides, i.MX27 ROM code does provide an indirect
vectors table but at a non-standard address and with
the reset and reserved vectors missing.

Turn the current vector relocation code into a weak
routine called after relocate_code from crt0, and add
strong version for i.MX27.

Series-Cc: Heiko Schocher <hs@denx.de>

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
Reviewed-by: Stefano Babic <sbabic@denx.de>
Tested-by: Stefano Babic <sbabic@denx.de>
Tested-by: Philippe Reynes <tremyfr@gmail.com>
Tested-by: Philippe Reynes <tremyfr@yahoo.fr>

arch/arm/cpu/arm926ejs/mx27/Makefile

@@ -5,3 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 
 obj-y	= generic.o reset.o timer.o
+
+ifndef CONFIG_SPL_BUILD
+obj-y	+= relocate.o
+endif

arch/arm/cpu/arm926ejs/mx27/relocate.S

@@ -0,0 +1,51 @@
+/*
+ *  relocate - i.MX27-specific vector relocation
+ *
+ *  Copyright (c) 2013  Albert ARIBAUD <albert.u.boot@aribaud.net>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <asm-offsets.h>
+#include <config.h>
+#include <linux/linkage.h>
+
+/*
+ * The i.MX27 SoC is very specific with respect to exceptions: it
+ * does not provide RAM at the high vectors address (0xFFFF0000),
+ * thus only the low address (0x00000000) is useable; but that is
+ * in ROM. Therefore, vectors cannot be changed at all.
+ *
+ * However, these ROM-based vectors actually just perform indirect
+ * calls through pointers located in RAM at SoC-specific addresses,
+ * as follows:
+ *
+ * Offset      Exception              Use by ROM code
+ * 0x00000000  reset                  indirect branch to [0x00000014]
+ * 0x00000004  undefined instruction  indirect branch to [0xfffffef0]
+ * 0x00000008  software interrupt     indirect branch to [0xfffffef4]
+ * 0x0000000c  prefetch abort         indirect branch to [0xfffffef8]
+ * 0x00000010  data abort             indirect branch to [0xfffffefc]
+ * 0x00000014  (reserved in ARMv5)    vector to ROM reset: 0xc0000000
+ * 0x00000018  IRQ                    indirect branch to [0xffffff00]
+ * 0x0000001c  FIQ                    indirect branch to [0xffffff04]
+ *
+ * In order to initialize exceptions on i.MX27, we must copy U-Boot's
+ * indirect (not exception!) vector table into 0xfffffef0..0xffffff04
+ * taking care not to copy vectors number 5 (reserved exception).
+ */
+
+	.section	.text.relocate_vectors,"ax",%progbits
+
+ENTRY(relocate_vectors)
+
+	ldr	r0, [r9, #GD_RELOCADDR]	/* r0 = gd->relocaddr */
+	ldr	r1, =32			/* size of vector table */
+	add	r0, r0, r1		/* skip to indirect table */
+	ldr	r1, =0xFFFFFEF0		/* i.MX27 indirect table */
+	ldmia	r0!, {r2-r8}		/* load indirect vectors 1..7 */
+	stmia	r1!, {r2-r5, r7,r8}	/* write all but vector 5 */
+
+	bx	lr
+
+ENDPROC(relocate_vectors)

arch/arm/lib/crt0.S

@@ -104,6 +104,11 @@ clr_gd:
 	ldr	r0, [r9, #GD_RELOCADDR]		/* r0 = gd->relocaddr */
 	b	relocate_code
 here:
+/*
+ * now relocate vectors
+ */
+
+	bl	relocate_vectors
 
 /* Set up final (full) environment */
 

arch/arm/lib/relocate.S

@@ -10,6 +10,47 @@
 #include <config.h>
 #include <linux/linkage.h>
 
+/*
+ * Default/weak exception vectors relocation routine
+ *
+ * This routine covers the standard ARM cases: normal (0x00000000),
+ * high (0xffff0000) and VBAR. SoCs which do not comply with any of
+ * the standard cases must provide their own, strong, version.
+ */
+
+	.section	.text.relocate_vectors,"ax",%progbits
+	.weak		relocate_vectors
+
+ENTRY(relocate_vectors)
+
+#ifdef CONFIG_HAS_VBAR
+	/*
+	 * If the ARM processor has the security extensions,
+	 * use VBAR to relocate the exception vectors.
+	 */
+	ldr	r0, [r9, #GD_RELOCADDR]	/* r0 = gd->relocaddr */
+	mcr     p15, 0, r0, c12, c0, 0  /* Set VBAR */
+#else
+	/*
+	 * Copy the relocated exception vectors to the
+	 * correct address
+	 * CP15 c1 V bit gives us the location of the vectors:
+	 * 0x00000000 or 0xFFFF0000.
+	 */
+	ldr	r0, [r9, #GD_RELOCADDR]	/* r0 = gd->relocaddr */
+	mrc	p15, 0, r2, c1, c0, 0	/* V bit (bit[13]) in CP15 c1 */
+	ands	r2, r2, #(1 << 13)
+	ldreq	r1, =0x00000000		/* If V=0 */
+	ldrne	r1, =0xFFFF0000		/* If V=1 */
+	ldmia	r0!, {r2-r8,r10}
+	stmia	r1!, {r2-r8,r10}
+	ldmia	r0!, {r2-r8,r10}
+	stmia	r1!, {r2-r8,r10}
+#endif
+	bx	lr
+
+ENDPROC(relocate_vectors)
+
 /*
  * void relocate_code(addr_moni)
  *
@@ -54,34 +95,6 @@ fixnext:
 	cmp	r2, r3
 	blo	fixloop
 
-	/*
-	 * Relocate the exception vectors
-	 */
-#ifdef CONFIG_HAS_VBAR
-	/*
-	 * If the ARM processor has the security extensions,
-	 * use VBAR to relocate the exception vectors.
-	 */
-	ldr	r0, [r9, #GD_RELOCADDR]	/* r0 = gd->relocaddr */
-	mcr     p15, 0, r0, c12, c0, 0  /* Set VBAR */
-#else
-	/*
-	 * Copy the relocated exception vectors to the
-	 * correct address
-	 * CP15 c1 V bit gives us the location of the vectors:
-	 * 0x00000000 or 0xFFFF0000.
-	 */
-	ldr	r0, [r9, #GD_RELOCADDR]	/* r0 = gd->relocaddr */
-	mrc	p15, 0, r2, c1, c0, 0	/* V bit (bit[13]) in CP15 c1 */
-	ands	r2, r2, #(1 << 13)
-	ldreq	r1, =0x00000000		/* If V=0 */
-	ldrne	r1, =0xFFFF0000		/* If V=1 */
-	ldmia	r0!, {r2-r8,r10}
-	stmia	r1!, {r2-r8,r10}
-	ldmia	r0!, {r2-r8,r10}
-	stmia	r1!, {r2-r8,r10}
-#endif
-
 relocate_done:
 
 #ifdef __XSCALE__