ARM: iwmmxt: Use undef hook to enable coprocessor for task

Define a undef hook to deal with undef exceptions triggered by iwmmxt
instructions that were issued with the coprocessor disabled. This
removes the dependency on the coprocessor dispatch code in entry-armv.S,
which will be made NWFPE-only in a subsequent patch.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Author: ardbiesheuvel

arch/arm/include/asm/thread_info.h

@@ -40,6 +40,7 @@ struct task_struct;
 DECLARE_PER_CPU(struct task_struct *, __entry_task);
 
 #include <asm/types.h>
+#include <asm/traps.h>
 
 struct cpu_context_save {
 	__u32	r4;
@@ -104,6 +105,21 @@ extern void iwmmxt_task_restore(struct thread_info *, void *);
 extern void iwmmxt_task_release(struct thread_info *);
 extern void iwmmxt_task_switch(struct thread_info *);
 
+extern int iwmmxt_undef_handler(struct pt_regs *, u32);
+
+static inline void register_iwmmxt_undef_handler(void)
+{
+	static struct undef_hook iwmmxt_undef_hook = {
+		.instr_mask	= 0x0c000e00,
+		.instr_val	= 0x0c000000,
+		.cpsr_mask	= MODE_MASK | PSR_T_BIT,
+		.cpsr_val	= USR_MODE,
+		.fn		= iwmmxt_undef_handler,
+	};
+
+	register_undef_hook(&iwmmxt_undef_hook);
+}
+
 extern void vfp_sync_hwstate(struct thread_info *);
 extern void vfp_flush_hwstate(struct thread_info *);
 

arch/arm/kernel/entry-armv.S

@@ -507,6 +507,7 @@ ARM_BE8(rev	r0, r0)				@ little endian instruction
 	ldr	r5, [r10, #TI_FLAGS]
 	rsbs	r7, r8, #(1 << 8)		@ CP 0 or 1 only
 	movscs	r7, r5, lsr #(TIF_USING_IWMMXT + 1)
+	movcs	r0, sp				@ pass struct pt_regs
 	bcs	iwmmxt_task_enable
 #endif
  ARM(	add	pc, pc, r8, lsr #6	)

arch/arm/kernel/iwmmxt.S

@@ -58,9 +58,19 @@
 	.text
 	.arm
 
+ENTRY(iwmmxt_undef_handler)
+	push		{r9, r10, lr}
+	get_thread_info	r10
+	mov		r9, pc
+	b		iwmmxt_task_enable
+	mov		r0, #0
+	pop		{r9, r10, pc}
+ENDPROC(iwmmxt_undef_handler)
+
 /*
  * Lazy switching of Concan coprocessor context
  *
+ * r0  = struct pt_regs pointer
  * r10 = struct thread_info pointer
  * r9  = ret_from_exception
  * lr  = undefined instr exit
@@ -84,12 +94,12 @@ ENTRY(iwmmxt_task_enable)
 	PJ4(mcr	p15, 0, r2, c1, c0, 2)
 
 	ldr	r3, =concan_owner
-	add	r0, r10, #TI_IWMMXT_STATE	@ get task Concan save area
-	ldr	r2, [sp, #60]			@ current task pc value
+	ldr	r2, [r0, #S_PC]			@ current task pc value
 	ldr	r1, [r3]			@ get current Concan owner
-	str	r0, [r3]			@ this task now owns Concan regs
 	sub	r2, r2, #4			@ adjust pc back
-	str	r2, [sp, #60]
+	str	r2, [r0, #S_PC]
+	add	r0, r10, #TI_IWMMXT_STATE	@ get task Concan save area
+	str	r0, [r3]			@ this task now owns Concan regs
 
 	mrc	p15, 0, r2, c2, c0, 0
 	mov	r2, r2				@ cpwait

arch/arm/kernel/pj4-cp0.c

@@ -126,6 +126,7 @@ static int __init pj4_cp0_init(void)
 	pr_info("PJ4 iWMMXt v%d coprocessor enabled.\n", vers);
 	elf_hwcap |= HWCAP_IWMMXT;
 	thread_register_notifier(&iwmmxt_notifier_block);
+	register_iwmmxt_undef_handler();
 #endif
 
 	return 0;

arch/arm/kernel/xscale-cp0.c

@@ -166,6 +166,7 @@ static int __init xscale_cp0_init(void)
 		pr_info("XScale iWMMXt coprocessor detected.\n");
 		elf_hwcap |= HWCAP_IWMMXT;
 		thread_register_notifier(&iwmmxt_notifier_block);
+		register_iwmmxt_undef_handler();
 #endif
 	} else {
 		pr_info("XScale DSP coprocessor detected.\n");