v4.19.13 snapshot.
diff --git a/arch/arm/kernel/xscale-cp0.c b/arch/arm/kernel/xscale-cp0.c
new file mode 100644
index 0000000..77a2eef
--- /dev/null
+++ b/arch/arm/kernel/xscale-cp0.c
@@ -0,0 +1,184 @@
+/*
+ * linux/arch/arm/kernel/xscale-cp0.c
+ *
+ * XScale DSP and iWMMXt coprocessor context switching and handling
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/signal.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <asm/thread_notify.h>
+#include <asm/cputype.h>
+
+asm(" .arch armv5te\n");
+
+static inline void dsp_save_state(u32 *state)
+{
+ __asm__ __volatile__ (
+ "mrrc p0, 0, %0, %1, c0\n"
+ : "=r" (state[0]), "=r" (state[1]));
+}
+
+static inline void dsp_load_state(u32 *state)
+{
+ __asm__ __volatile__ (
+ "mcrr p0, 0, %0, %1, c0\n"
+ : : "r" (state[0]), "r" (state[1]));
+}
+
+static int dsp_do(struct notifier_block *self, unsigned long cmd, void *t)
+{
+ struct thread_info *thread = t;
+
+ switch (cmd) {
+ case THREAD_NOTIFY_FLUSH:
+ thread->cpu_context.extra[0] = 0;
+ thread->cpu_context.extra[1] = 0;
+ break;
+
+ case THREAD_NOTIFY_SWITCH:
+ dsp_save_state(current_thread_info()->cpu_context.extra);
+ dsp_load_state(thread->cpu_context.extra);
+ break;
+ }
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block dsp_notifier_block = {
+ .notifier_call = dsp_do,
+};
+
+
+#ifdef CONFIG_IWMMXT
+static int iwmmxt_do(struct notifier_block *self, unsigned long cmd, void *t)
+{
+ struct thread_info *thread = t;
+
+ switch (cmd) {
+ case THREAD_NOTIFY_FLUSH:
+ /*
+ * flush_thread() zeroes thread->fpstate, so no need
+ * to do anything here.
+ *
+ * FALLTHROUGH: Ensure we don't try to overwrite our newly
+ * initialised state information on the first fault.
+ */
+
+ case THREAD_NOTIFY_EXIT:
+ iwmmxt_task_release(thread);
+ break;
+
+ case THREAD_NOTIFY_SWITCH:
+ iwmmxt_task_switch(thread);
+ break;
+ }
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block iwmmxt_notifier_block = {
+ .notifier_call = iwmmxt_do,
+};
+#endif
+
+
+static u32 __init xscale_cp_access_read(void)
+{
+ u32 value;
+
+ __asm__ __volatile__ (
+ "mrc p15, 0, %0, c15, c1, 0\n\t"
+ : "=r" (value));
+
+ return value;
+}
+
+static void __init xscale_cp_access_write(u32 value)
+{
+ u32 temp;
+
+ __asm__ __volatile__ (
+ "mcr p15, 0, %1, c15, c1, 0\n\t"
+ "mrc p15, 0, %0, c15, c1, 0\n\t"
+ "mov %0, %0\n\t"
+ "sub pc, pc, #4\n\t"
+ : "=r" (temp) : "r" (value));
+}
+
+/*
+ * Detect whether we have a MAC coprocessor (40 bit register) or an
+ * iWMMXt coprocessor (64 bit registers) by loading 00000100:00000000
+ * into a coprocessor register and reading it back, and checking
+ * whether the upper word survived intact.
+ */
+static int __init cpu_has_iwmmxt(void)
+{
+ u32 lo;
+ u32 hi;
+
+ /*
+ * This sequence is interpreted by the DSP coprocessor as:
+ * mar acc0, %2, %3
+ * mra %0, %1, acc0
+ *
+ * And by the iWMMXt coprocessor as:
+ * tmcrr wR0, %2, %3
+ * tmrrc %0, %1, wR0
+ */
+ __asm__ __volatile__ (
+ "mcrr p0, 0, %2, %3, c0\n"
+ "mrrc p0, 0, %0, %1, c0\n"
+ : "=r" (lo), "=r" (hi)
+ : "r" (0), "r" (0x100));
+
+ return !!hi;
+}
+
+
+/*
+ * If we detect that the CPU has iWMMXt (and CONFIG_IWMMXT=y), we
+ * disable CP0/CP1 on boot, and let call_fpe() and the iWMMXt lazy
+ * switch code handle iWMMXt context switching. If on the other
+ * hand the CPU has a DSP coprocessor, we keep access to CP0 enabled
+ * all the time, and save/restore acc0 on context switch in non-lazy
+ * fashion.
+ */
+static int __init xscale_cp0_init(void)
+{
+ u32 cp_access;
+
+ /* do not attempt to probe iwmmxt on non-xscale family CPUs */
+ if (!cpu_is_xscale_family())
+ return 0;
+
+ cp_access = xscale_cp_access_read() & ~3;
+ xscale_cp_access_write(cp_access | 1);
+
+ if (cpu_has_iwmmxt()) {
+#ifndef CONFIG_IWMMXT
+ pr_warn("CAUTION: XScale iWMMXt coprocessor detected, but kernel support is missing.\n");
+#else
+ pr_info("XScale iWMMXt coprocessor detected.\n");
+ elf_hwcap |= HWCAP_IWMMXT;
+ thread_register_notifier(&iwmmxt_notifier_block);
+#endif
+ } else {
+ pr_info("XScale DSP coprocessor detected.\n");
+ thread_register_notifier(&dsp_notifier_block);
+ cp_access |= 1;
+ }
+
+ xscale_cp_access_write(cp_access);
+
+ return 0;
+}
+
+late_initcall(xscale_cp0_init);