[ARM] 4582/2: Add support for the common VFP subarchitecture

This patch allows the VFP support code to run correctly on CPUs
compatible with the common VFP subarchitecture specification (Appendix
B in the ARM ARM v7-A and v7-R edition). It implements support for VFP
subarchitecture 2 while being backwards compatible with
subarchitecture 1.

On VFP subarchitecture 1, the arithmetic exceptions are asynchronous
(or imprecise as described in the old ARM ARM) unless the FPSCR.IXE
bit is 1. The exceptional instructions can be read from FPINST and
FPINST2 registers. With VFP subarchitecture 2, the arithmetic
exceptions can also be synchronous and marked by the FPEXC.DEX bit
(the FPEXC.EX bit is cleared). CPUs implementing the synchronous
arithmetic exceptions don't have the FPINST and FPINST2 registers and
accessing them would trigger and undefined exception.

Note that FPEXC.EX bit has an additional meaning on subarchitecture 1
- if it isn't set, there is no additional information in FPINST and
FPINST2 that needs to be saved at context switch or when lazy-loading
the VFP state of a different thread.

The patch also removes the clearing of the cumulative exception flags in
FPSCR when additional exceptions were raised. It is up to the user
application to clear these bits.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 55 insertions, 43 deletions

diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index b4e210d..32455c6 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -125,13 +125,13 @@ void vfp_raise_sigfpe(unsigned int sicode, struct pt_regs *regs)
 	send_sig_info(SIGFPE, &info, current);
 }
 
-static void vfp_panic(char *reason)
+static void vfp_panic(char *reason, u32 inst)
 {
 	int i;
 
 	printk(KERN_ERR "VFP: Error: %s\n", reason);
 	printk(KERN_ERR "VFP: EXC 0x%08x SCR 0x%08x INST 0x%08x\n",
-		fmrx(FPEXC), fmrx(FPSCR), fmrx(FPINST));
+		fmrx(FPEXC), fmrx(FPSCR), inst);
 	for (i = 0; i < 32; i += 2)
 		printk(KERN_ERR "VFP: s%2u: 0x%08x s%2u: 0x%08x\n",
 		       i, vfp_get_float(i), i+1, vfp_get_float(i+1));
@@ -147,19 +147,16 @@ static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_
 	pr_debug("VFP: raising exceptions %08x\n", exceptions);
 
 	if (exceptions == VFP_EXCEPTION_ERROR) {
-		vfp_panic("unhandled bounce");
+		vfp_panic("unhandled bounce", inst);
 		vfp_raise_sigfpe(0, regs);
 		return;
 	}
 
 	/*
-	 * If any of the status flags are set, update the FPSCR.
+	 * Update the FPSCR with the additional exception flags.
 	 * Comparison instructions always return at least one of
 	 * these flags set.
 	 */
-	if (exceptions & (FPSCR_N|FPSCR_Z|FPSCR_C|FPSCR_V))
-		fpscr &= ~(FPSCR_N|FPSCR_Z|FPSCR_C|FPSCR_V);
-
 	fpscr |= exceptions;
 
 	fmxr(FPSCR, fpscr);
@@ -220,35 +217,64 @@ static u32 vfp_emulate_instruction(u32 inst, u32 fpscr, struct pt_regs *regs)
 /*
  * Package up a bounce condition.
  */
-void VFP9_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
+void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 {
-	u32 fpscr, orig_fpscr, exceptions, inst;
+	u32 fpscr, orig_fpscr, fpsid, exceptions;
 
 	pr_debug("VFP: bounce: trigger %08x fpexc %08x\n", trigger, fpexc);
 
 	/*
-	 * Enable access to the VFP so we can handle the bounce.
+	 * At this point, FPEXC can have the following configuration:
+	 *
+	 *  EX DEX IXE
+	 *  0   1   x   - synchronous exception
+	 *  1   x   0   - asynchronous exception
+	 *  1   x   1   - sychronous on VFP subarch 1 and asynchronous on later
+	 *  0   0   1   - synchronous on VFP9 (non-standard subarch 1
+	 *                implementation), undefined otherwise
+	 *
+	 * Clear various bits and enable access to the VFP so we can
+	 * handle the bounce.
 	 */
-	fmxr(FPEXC, fpexc & ~(FPEXC_EX|FPEXC_FPV2|FPEXC_INV|FPEXC_UFC|FPEXC_OFC|FPEXC_IOC));
+	fmxr(FPEXC, fpexc & ~(FPEXC_EX|FPEXC_DEX|FPEXC_FP2V|FPEXC_VV|FPEXC_TRAP_MASK));
 
+	fpsid = fmrx(FPSID);
 	orig_fpscr = fpscr = fmrx(FPSCR);
 
 	/*
-	 * If we are running with inexact exceptions enabled, we need to
-	 * emulate the trigger instruction.  Note that as we're emulating
-	 * the trigger instruction, we need to increment PC.
+	 * Check for the special VFP subarch 1 and FPSCR.IXE bit case
 	 */
-	if (fpscr & FPSCR_IXE) {
-		regs->ARM_pc += 4;
+	if ((fpsid & FPSID_ARCH_MASK) == (1 << FPSID_ARCH_BIT)
+	    && (fpscr & FPSCR_IXE)) {
+		/*
+		 * Synchronous exception, emulate the trigger instruction
+		 */
 		goto emulate;
 	}
 
-	barrier();
+	if (fpexc & FPEXC_EX) {
+		/*
+		 * Asynchronous exception. The instruction is read from FPINST
+		 * and the interrupted instruction has to be restarted.
+		 */
+		trigger = fmrx(FPINST);
+		regs->ARM_pc -= 4;
+	} else if (!(fpexc & FPEXC_DEX)) {
+		/*
+		 * Illegal combination of bits. It can be caused by an
+		 * unallocated VFP instruction but with FPSCR.IXE set and not
+		 * on VFP subarch 1.
+		 */
+		 vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr, regs);
+		 return;
+	}
 
 	/*
-	 * Modify fpscr to indicate the number of iterations remaining
+	 * Modify fpscr to indicate the number of iterations remaining.
+	 * If FPEXC.EX is 0, FPEXC.DEX is 1 and the FPEXC.VV bit indicates
+	 * whether FPEXC.VECITR or FPSCR.LEN is used.
 	 */
-	if (fpexc & FPEXC_EX) {
+	if (fpexc & (FPEXC_EX | FPEXC_VV)) {
 		u32 len;
 
 		len = fpexc + (1 << FPEXC_LENGTH_BIT);
@@ -262,15 +288,15 @@ void VFP9_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 	 * FPEXC bounce reason, but this appears to be unreliable.
 	 * Emulate the bounced instruction instead.
 	 */
-	inst = fmrx(FPINST);
-	exceptions = vfp_emulate_instruction(inst, fpscr, regs);
+	exceptions = vfp_emulate_instruction(trigger, fpscr, regs);
 	if (exceptions)
-		vfp_raise_exceptions(exceptions, inst, orig_fpscr, regs);
+		vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
 
 	/*
-	 * If there isn't a second FP instruction, exit now.
+	 * If there isn't a second FP instruction, exit now. Note that
+	 * the FPEXC.FP2V bit is valid only if FPEXC.EX is 1.
 	 */
-	if (!(fpexc & FPEXC_FPV2))
+	if (fpexc ^ (FPEXC_EX | FPEXC_FP2V))
 		return;
 
 	/*
@@ -279,10 +305,9 @@ void VFP9_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 	 */
 	barrier();
 	trigger = fmrx(FPINST2);
-	orig_fpscr = fpscr = fmrx(FPSCR);
 
  emulate:
-	exceptions = vfp_emulate_instruction(trigger, fpscr, regs);
+	exceptions = vfp_emulate_instruction(trigger, orig_fpscr, regs);
 	if (exceptions)
 		vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs);
 }
@@ -306,16 +331,9 @@ static int __init vfp_init(void)
 {
 	unsigned int vfpsid;
 	unsigned int cpu_arch = cpu_architecture();
-	u32 access = 0;
 
-	if (cpu_arch >= CPU_ARCH_ARMv6) {
-		access = get_copro_access();
-
-		/*
-		 * Enable full access to VFP (cp10 and cp11)
-		 */
-		set_copro_access(access | CPACC_FULL(10) | CPACC_FULL(11));
-	}
+	if (cpu_arch >= CPU_ARCH_ARMv6)
+		vfp_enable(NULL);
 
 	/*
 	 * First check that there is a VFP that we can use.
@@ -329,15 +347,9 @@ static int __init vfp_init(void)
 	vfp_vector = vfp_null_entry;
 
 	printk(KERN_INFO "VFP support v0.3: ");
-	if (VFP_arch) {
+	if (VFP_arch)
 		printk("not present\n");
-
-		/*
-		 * Restore the copro access register.
-		 */
-		if (cpu_arch >= CPU_ARCH_ARMv6)
-			set_copro_access(access);
-	} else if (vfpsid & FPSID_NODOUBLE) {
+	else if (vfpsid & FPSID_NODOUBLE) {
 		printk("no double precision support\n");
 	} else {
 		smp_call_function(vfp_enable, NULL, 1, 1);