[ARM] ARMv7 errata: only apply fixes when running on applicable CPU

Currently, whenever an erratum workaround is enabled, it will be
applied whether or not the erratum is relevent for the CPU.  This
patch changes this - we check the variant and revision fields in the
main ID register to determine which errata to apply.

We also avoid re-applying erratum 460075 if it has already been applied.
Applying this fix in non-secure mode results in the kernel failing to
boot (or even do anything.)

This fixes booting on some ARMv7 based platforms which otherwise
silently fail.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/proc-v7.S

@@ -184,23 +184,37 @@ __v7_setup:
 	stmia	r12, {r0-r5, r7, r9, r11, lr}
 	bl	v7_flush_dcache_all
 	ldmia	r12, {r0-r5, r7, r9, r11, lr}
+
+	mrc	p15, 0, r0, c0, c0, 0		@ read main ID register
+	and	r10, r0, #0xff000000		@ ARM?
+	teq	r10, #0x41000000
+	bne	2f
+	and	r5, r0, #0x00f00000		@ variant
+	and	r6, r0, #0x0000000f		@ revision
+	orr	r0, r6, r5, lsr #20-4		@ combine variant and revision
+
 #ifdef CONFIG_ARM_ERRATA_430973
-	mrc	p15, 0, r10, c1, c0, 1		@ read aux control register
-	orr	r10, r10, #(1 << 6)		@ set IBE to 1
-	mcr	p15, 0, r10, c1, c0, 1		@ write aux control register
+	teq	r5, #0x00100000			@ only present in r1p*
+	mrceq	p15, 0, r10, c1, c0, 1		@ read aux control register
+	orreq	r10, r10, #(1 << 6)		@ set IBE to 1
+	mcreq	p15, 0, r10, c1, c0, 1		@ write aux control register
 #endif
 #ifdef CONFIG_ARM_ERRATA_458693
-	mrc	p15, 0, r10, c1, c0, 1		@ read aux control register
-	orr	r10, r10, #(1 << 5)		@ set L1NEON to 1
-	orr	r10, r10, #(1 << 9)		@ set PLDNOP to 1
-	mcr	p15, 0, r10, c1, c0, 1		@ write aux control register
+	teq	r0, #0x20			@ only present in r2p0
+	mrceq	p15, 0, r10, c1, c0, 1		@ read aux control register
+	orreq	r10, r10, #(1 << 5)		@ set L1NEON to 1
+	orreq	r10, r10, #(1 << 9)		@ set PLDNOP to 1
+	mcreq	p15, 0, r10, c1, c0, 1		@ write aux control register
 #endif
 #ifdef CONFIG_ARM_ERRATA_460075
-	mrc	p15, 1, r10, c9, c0, 2		@ read L2 cache aux ctrl register
-	orr	r10, r10, #(1 << 22)		@ set the Write Allocate disable bit
-	mcr	p15, 1, r10, c9, c0, 2		@ write the L2 cache aux ctrl register
+	teq	r0, #0x20			@ only present in r2p0
+	mrceq	p15, 1, r10, c9, c0, 2		@ read L2 cache aux ctrl register
+	tsteq	r10, #1 << 22
+	orreq	r10, r10, #(1 << 22)		@ set the Write Allocate disable bit
+	mcreq	p15, 1, r10, c9, c0, 2		@ write the L2 cache aux ctrl register
 #endif
-	mov	r10, #0
+
+2:	mov	r10, #0
 #ifdef HARVARD_CACHE
 	mcr	p15, 0, r10, c7, c5, 0		@ I+BTB cache invalidate
 #endif