--- zzzz-none-000/linux-3.10.107/arch/arm/kernel/pj4-cp0.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/arch/arm/kernel/pj4-cp0.c	2021-02-04 17:41:59.000000000 +0000
@@ -17,6 +17,7 @@
 #include <linux/init.h>
 #include <linux/io.h>
 #include <asm/thread_notify.h>
+#include <asm/cputype.h>
 
 static int iwmmxt_do(struct notifier_block *self, unsigned long cmd, void *t)
 {
@@ -44,7 +45,7 @@
 	return NOTIFY_DONE;
 }
 
-static struct notifier_block iwmmxt_notifier_block = {
+static struct notifier_block __maybe_unused iwmmxt_notifier_block = {
 	.notifier_call	= iwmmxt_do,
 };
 
@@ -71,6 +72,33 @@
 		: "=r" (temp) : "r" (value));
 }
 
+static int __init pj4_get_iwmmxt_version(void)
+{
+	u32 cp_access, wcid;
+
+	cp_access = pj4_cp_access_read();
+	pj4_cp_access_write(cp_access | 0xf);
+
+	/* check if coprocessor 0 and 1 are available */
+	if ((pj4_cp_access_read() & 0xf) != 0xf) {
+		pj4_cp_access_write(cp_access);
+		return -ENODEV;
+	}
+
+	/* read iWMMXt coprocessor id register p1, c0 */
+	__asm__ __volatile__ ("mrc    p1, 0, %0, c0, c0, 0\n" : "=r" (wcid));
+
+	pj4_cp_access_write(cp_access);
+
+	/* iWMMXt v1 */
+	if ((wcid & 0xffffff00) == 0x56051000)
+		return 1;
+	/* iWMMXt v2 */
+	if ((wcid & 0xffffff00) == 0x56052000)
+		return 2;
+
+	return -EINVAL;
+}
 
 /*
  * Disable CP0/CP1 on boot, and let call_fpe() and the iWMMXt lazy
@@ -78,14 +106,26 @@
  */
 static int __init pj4_cp0_init(void)
 {
-	u32 cp_access;
+	u32 __maybe_unused cp_access;
+	int vers;
+
+	if (!cpu_is_pj4())
+		return 0;
 
+	vers = pj4_get_iwmmxt_version();
+	if (vers < 0)
+		return 0;
+
+#ifndef CONFIG_IWMMXT
+	pr_info("PJ4 iWMMXt coprocessor detected, but kernel support is missing.\n");
+#else
 	cp_access = pj4_cp_access_read() & ~0xf;
 	pj4_cp_access_write(cp_access);
 
-	printk(KERN_INFO "PJ4 iWMMXt coprocessor enabled.\n");
+	pr_info("PJ4 iWMMXt v%d coprocessor enabled.\n", vers);
 	elf_hwcap |= HWCAP_IWMMXT;
 	thread_register_notifier(&iwmmxt_notifier_block);
+#endif
 
 	return 0;
 }