[PATCH] ppc64: Detect altivec via firmware on unknown CPUs

This patch adds detection of the Altivec capability of the CPU via the
firmware in addition to the cpu table.  This allows newer CPUs that aren't
in the table to still have working altivec support in the kernel.

It also fixes a problem where if a CPU isn't recognized as having altivec
features, and takes an altivec unavailable exception due to userland
issuing altivec instructions, the kernel would happily enable it and
context switch the registers ...  but not all of them (it would basically
forget vrsave).  With this patch, the kernel will refuse to enable altivec
when the feature isn't detected for the CPU (SIGILL).
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/head.S

@@ -922,7 +922,9 @@ fp_unavailable_common:
 altivec_unavailable_common:
 	EXCEPTION_PROLOG_COMMON(0xf20, PACA_EXGEN)
 #ifdef CONFIG_ALTIVEC
+BEGIN_FTR_SECTION
 	bne	.load_up_altivec	/* if from user, just load it up */
+END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
 #endif
 	bl	.save_nvgprs
 	addi	r3,r1,STACK_FRAME_OVERHEAD

arch/ppc64/kernel/prom.c

@@ -885,6 +885,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 					  const char *full_path, void *data)
 {
 	char *type = get_flat_dt_prop(node, "device_type", NULL);
+	u32 *prop;
 
 	/* We are scanning "cpu" nodes only */
 	if (type == NULL || strcmp(type, "cpu") != 0)
@@ -916,6 +917,20 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 		}
 	}
 
+	/* Check if we have a VMX and eventually update CPU features */
+	prop = (u32 *)get_flat_dt_prop(node, "ibm,vmx", NULL);
+	if (prop && (*prop) > 0) {
+		cur_cpu_spec->cpu_features |= CPU_FTR_ALTIVEC;
+		cur_cpu_spec->cpu_user_features |= PPC_FEATURE_HAS_ALTIVEC;
+	}
+
+	/* Same goes for Apple's "altivec" property */
+	prop = (u32 *)get_flat_dt_prop(node, "altivec", NULL);
+	if (prop) {
+		cur_cpu_spec->cpu_features |= CPU_FTR_ALTIVEC;
+		cur_cpu_spec->cpu_user_features |= PPC_FEATURE_HAS_ALTIVEC;
+	}
+
 	return 0;
 }
 
@@ -1104,7 +1119,9 @@ void __init early_init_devtree(void *params)
 
 	DBG("Scanning CPUs ...\n");
 
-	/* Retreive hash table size from flattened tree */
+	/* Retreive hash table size from flattened tree plus other
+	 * CPU related informations (altivec support, boot CPU ID, ...)
+	 */
 	scan_flat_dt(early_init_dt_scan_cpus, NULL);
 
 	/* If hash size wasn't obtained above, we calculate it now based on

arch/ppc64/kernel/traps.c

@@ -450,14 +450,12 @@ void kernel_fp_unavailable_exception(struct pt_regs *regs)
 
 void altivec_unavailable_exception(struct pt_regs *regs)
 {
-#ifndef CONFIG_ALTIVEC
 	if (user_mode(regs)) {
 		/* A user program has executed an altivec instruction,
 		   but this kernel doesn't support altivec. */
 		_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
 		return;
 	}
-#endif
 	printk(KERN_EMERG "Unrecoverable VMX/Altivec Unavailable Exception "
 			  "%lx at %lx\n", regs->trap, regs->nip);
 	die("Unrecoverable VMX/Altivec Unavailable Exception", regs, SIGABRT);