ARM: mstar: Add machine for MStar/Sigmastar Armv7 SoCs

Initial support for the MStar/Sigmastar Armv7 based IP camera
and dashcam SoCs.

These chips are interesting in that they contain a Cortex-A7,
peripherals and system memory in a single tiny QFN package that
can be hand soldered allowing almost anyone to embed Linux
in their projects.
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

MAINTAINERS

@@ -2140,6 +2140,7 @@ L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 W:	http://linux-chenxing.org/
 F:	Documentation/devicetree/bindings/arm/mstar.yaml
+F:	arch/arm/mach-mstar/
 
 ARM/NEC MOBILEPRO 900/c MACHINE SUPPORT
 M:	Michael Petchkovsky <mkpetch@internode.on.net>

arch/arm/Kconfig

@@ -668,6 +668,8 @@ source "arch/arm/mach-mmp/Kconfig"
 
 source "arch/arm/mach-moxart/Kconfig"
 
+source "arch/arm/mach-mstar/Kconfig"
+
 source "arch/arm/mach-mv78xx0/Kconfig"
 
 source "arch/arm/mach-mvebu/Kconfig"

arch/arm/Makefile

@@ -197,6 +197,7 @@ machine-$(CONFIG_ARCH_MXC)		+= imx
 machine-$(CONFIG_ARCH_MEDIATEK)		+= mediatek
 machine-$(CONFIG_ARCH_MILBEAUT)		+= milbeaut
 machine-$(CONFIG_ARCH_MXS)		+= mxs
+machine-$(CONFIG_ARCH_MSTARV7)		+= mstar
 machine-$(CONFIG_ARCH_NOMADIK)		+= nomadik
 machine-$(CONFIG_ARCH_NPCM)		+= npcm
 machine-$(CONFIG_ARCH_NSPIRE)		+= nspire

arch/arm/mach-mstar/Kconfig

+menuconfig ARCH_MSTARV7
+	bool "MStar/Sigmastar Armv7 SoC Support"
+	depends on ARCH_MULTI_V7
+	select ARM_GIC
+	select ARM_HEAVY_MB
+	help
+	  Support for newer MStar/Sigmastar SoC families that are
+	  based on Armv7 cores like the Cortex A7 and share the same
+	  basic hardware like the infinity and mercury series.
+
+if ARCH_MSTARV7
+
+config MACH_INFINITY
+	bool "MStar/Sigmastar infinity SoC support"
+	default ARCH_MSTARV7
+	help
+	  Support for MStar/Sigmastar infinity IP camera SoCs.
+
+config MACH_MERCURY
+	bool "MStar/Sigmastar mercury SoC support"
+	default ARCH_MSTARV7
+	help
+	  Support for MStar/Sigmastar mercury dash camera SoCs.
+	  Note that older Mercury2 SoCs are ARM9 based and not supported.
+
+endif

arch/arm/mach-mstar/Makefile

+obj-$(CONFIG_ARCH_MSTARV7) += mstarv7.o

arch/arm/mach-mstar/mstarv7.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Device Tree support for MStar/Sigmastar Armv7 SoCs
+ *
+ * Copyright (c) 2020 thingy.jp
+ * Author: Daniel Palmer <daniel@thingy.jp>
+ */
+
+#include <linux/init.h>
+#include <asm/mach/arch.h>
+#include <asm/mach/map.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/io.h>
+
+/*
+ * In the u-boot code the area these registers are in is
+ * called "L3 bridge" and there are register descriptions
+ * for something in the same area called "AXI".
+ *
+ * It's not exactly known what this is but the vendor code
+ * for both u-boot and linux share calls to "flush the miu pipe".
+ * This seems to be to force pending CPU writes to memory so that
+ * the state is right before DMA capable devices try to read
+ * descriptors and data the CPU has prepared. Without doing this
+ * ethernet doesn't work reliably for example.
+ */
+
+#define MSTARV7_L3BRIDGE_FLUSH		0x14
+#define MSTARV7_L3BRIDGE_STATUS		0x40
+#define MSTARV7_L3BRIDGE_FLUSH_TRIGGER	BIT(0)
+#define MSTARV7_L3BRIDGE_STATUS_DONE	BIT(12)
+
+static void __iomem *l3bridge;
+
+static const char * const mstarv7_board_dt_compat[] __initconst = {
+	"mstar,infinity",
+	"mstar,infinity3",
+	"mstar,mercury5",
+	NULL,
+};
+
+/*
+ * This may need locking to deal with situations where an interrupt
+ * happens while we are in here and mb() gets called by the interrupt handler.
+ *
+ * The vendor code did have a spin lock but it doesn't seem to be needed and
+ * removing it hasn't caused any side effects so far.
+ *
+ * [writel|readl]_relaxed have to be used here because otherwise
+ * we'd end up right back in here.
+ */
+static void mstarv7_mb(void)
+{
+	/* toggle the flush miu pipe fire bit */
+	writel_relaxed(0, l3bridge + MSTARV7_L3BRIDGE_FLUSH);
+	writel_relaxed(MSTARV7_L3BRIDGE_FLUSH_TRIGGER, l3bridge
+			+ MSTARV7_L3BRIDGE_FLUSH);
+	while (!(readl_relaxed(l3bridge + MSTARV7_L3BRIDGE_STATUS)
+			& MSTARV7_L3BRIDGE_STATUS_DONE)) {
+		/* wait for flush to complete */
+	}
+}
+
+static void __init mstarv7_init(void)
+{
+	struct device_node *np;
+
+	np = of_find_compatible_node(NULL, NULL, "mstar,l3bridge");
+	l3bridge = of_iomap(np, 0);
+	if (l3bridge)
+		soc_mb = mstarv7_mb;
+	else
+		pr_warn("Failed to install memory barrier, DMA will be broken!\n");
+}
+
+DT_MACHINE_START(MSTARV7_DT, "MStar/Sigmastar Armv7 (Device Tree)")
+	.dt_compat	= mstarv7_board_dt_compat,
+	.init_machine	= mstarv7_init,
+MACHINE_END