Add AltiVec RAID-Z

Implements the RAID-Z function using AltiVec SIMD.
This is basically the NEON code translated to AltiVec.

Note that the 'fletcher' algorithm requires 64-bits
operations, and the initial implementations of AltiVec
(PPC74xx a.k.a. G4, PPC970 a.k.a. G5) only has up to
32-bits operations, so no 'fletcher'.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Romain Dolbeau <romain.dolbeau@european-processor-initiative.eu>
Closes #9539

include/os/linux/kernel/linux/Makefile.am

@@ -10,6 +10,7 @@ KERNEL_H = \
 	$(top_srcdir)/include/os/linux/kernel/linux/simd.h \
 	$(top_srcdir)/include/os/linux/kernel/linux/simd_x86.h \
 	$(top_srcdir)/include/os/linux/kernel/linux/simd_aarch64.h \
+	$(top_srcdir)/include/os/linux/kernel/linux/simd_powerpc.h \
 	$(top_srcdir)/include/os/linux/kernel/linux/mod_compat.h \
 	$(top_srcdir)/include/os/linux/kernel/linux/page_compat.h \
 	$(top_srcdir)/include/os/linux/kernel/linux/compiler_compat.h

include/os/linux/kernel/linux/simd.h

@@ -30,6 +30,9 @@
 
 #elif defined(__aarch64__)
 #include <linux/simd_aarch64.h>
+
+#elif defined(__powerpc__)
+#include <linux/simd_powerpc.h>
 #else
 
 #define	kfpu_allowed()		0

include/os/linux/kernel/linux/simd_powerpc.h

@@ -0,0 +1,109 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (C) 2019 Romain Dolbeau
+ *           <romain.dolbeau@european-processor-initiative.eu>
+ */
+
+/*
+ * USER API:
+ *
+ * Kernel fpu methods:
+ *	kfpu_allowed()
+ *	kfpu_begin()
+ *	kfpu_end()
+ *	kfpu_init()
+ *	kfpu_fini()
+ *
+ * SIMD support:
+ *
+ * Following functions should be called to determine whether CPU feature
+ * is supported. All functions are usable in kernel and user space.
+ * If a SIMD algorithm is using more than one instruction set
+ * all relevant feature test functions should be called.
+ *
+ * Supported features:
+ *	zfs_altivec_available()
+ */
+
+#ifndef _LINUX_SIMD_POWERPC_H
+#define	_LINUX_SIMD_POWERPC_H
+
+/* only for __powerpc__ */
+#if defined(__powerpc__)
+
+#include <linux/preempt.h>
+#include <linux/export.h>
+#include <linux/sched.h>
+#include <asm/switch_to.h>
+#include <sys/types.h>
+#include <linux/version.h>
+
+#define	kfpu_allowed()		1
+#define	kfpu_begin()					\
+	{						\
+		preempt_disable();			\
+		enable_kernel_altivec();		\
+	}
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 5, 0)
+#define	kfpu_end()				\
+	{					\
+		disable_kernel_altivec();	\
+		preempt_enable();		\
+	}
+#else
+/* seems that before 4.5 no-one bothered disabling ... */
+#define	kfpu_end()		preempt_enable()
+#endif
+#define	kfpu_init()		0
+#define	kfpu_fini()		((void) 0)
+
+/*
+ * Check if AltiVec instruction set is available
+ */
+static inline boolean_t
+zfs_altivec_available(void)
+{
+	boolean_t res;
+	/* suggested by macallan at netbsd dot org */
+#if defined(__powerpc64__)
+	u64 msr;
+#else
+	u32 msr;
+#endif
+	kfpu_begin();
+	__asm volatile("mfmsr %0" : "=r"(msr));
+	/*
+	 * 64 bits -> need to check bit 38
+	 * Power ISA Version 3.0B
+	 * p944
+	 * 32 bits -> Need to check bit 6
+	 * AltiVec Technology Programming Environments Manual
+	 * p49 (2-9)
+	 * They are the same, as ppc counts 'backward' ...
+	 */
+	res = (msr & 0x2000000) != 0;
+	kfpu_end();
+	return (res);
+}
+#endif /* defined(__powerpc) */
+
+#endif /* _LINUX_SIMD_POWERPC_H */