powerpc: Add Microwatt platform

Microwatt is a FPGA-based implementation of the Power ISA. It
currently only implements little-endian 64-bit mode, and does
not (yet) support SMP, VMX, VSX or transactional memory. It has an
optional FPU, and an optional MMU (required for running Linux,
obviously) which implements a configurable radix tree but not
hypervisor mode or nested radix translation.

This adds a new machine type to support FPGA-based SoCs with a
Microwatt core. CONFIG_MATH_EMULATION can be selected for Microwatt
SOCs which don't have the FPU.

Signed-off-by: Paul Mackerras <[e-mail]>
Reviewed-by: Nicholas Piggin <[e-mail]>
Reviewed-by: Segher Boessenkool <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/Kconfig

···
 
 config MATH_EMULATION
 	bool "Math emulation"
-	depends on 4xx || PPC_8xx || PPC_MPC832x || BOOKE
+	depends on 4xx || PPC_8xx || PPC_MPC832x || BOOKE || PPC_MICROWATT
 	select PPC_FPU_REGS
 	help
 	  Some PowerPC chips designed for embedded applications do not have

arch/powerpc/platforms/Kconfig

···
 source "arch/powerpc/platforms/40x/Kconfig"
 source "arch/powerpc/platforms/amigaone/Kconfig"
 source "arch/powerpc/platforms/book3s/Kconfig"
+source "arch/powerpc/platforms/microwatt/Kconfig"
 
 config KVM_GUEST
 	bool "KVM Guest support"

arch/powerpc/platforms/Makefile

···
 obj-$(CONFIG_EMBEDDED6xx)	+= embedded6xx/
 obj-$(CONFIG_AMIGAONE)		+= amigaone/
 obj-$(CONFIG_PPC_BOOK3S)	+= book3s/
+obj-$(CONFIG_PPC_MICROWATT)	+= microwatt/

arch/powerpc/platforms/microwatt/Kconfig

···
+# SPDX-License-Identifier: GPL-2.0
+config PPC_MICROWATT
+	depends on PPC_BOOK3S_64 && !SMP
+	bool "Microwatt SoC platform"
+	select PPC_XICS
+	select PPC_NATIVE
+	help
+          This option enables support for FPGA-based Microwatt implementations.
+

arch/powerpc/platforms/microwatt/Makefile

···
+obj-y	+= setup.o

arch/powerpc/platforms/microwatt/setup.c

···
+/*
+ * Microwatt FPGA-based SoC platform setup code.
+ *
+ * Copyright 2020 Paul Mackerras ([e-mail]), IBM Corp.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/stddef.h>
+#include <linux/init.h>
+#include <asm/machdep.h>
+#include <asm/time.h>
+
+static int __init microwatt_probe(void)
+{
+	return of_machine_is_compatible("microwatt-soc");
+}
+
+define_machine(microwatt) {
+	.name			= "microwatt",
+	.probe			= microwatt_probe,
+	.calibrate_decr		= generic_calibrate_decr,
+};