bus: uniphier-system-bus: add UniPhier System Bus driver

The UniPhier System Bus is an external bus that connects on-board
devices to the UniPhier SoC.  Each bank (chip select) is dynamically
mapped to the CPU-viewed address base via the bus controller.  The
bus controller must be configured before any access to the bus.

This driver parses the "ranges" property of the System Bus node and
initialized the bus controller.  After the bus becomes ready, devices
below it are populated.

Note:
Each bank can be mapped anywhere in the supported address space;
there is nothing preventing us from assigning bank 0 on 0x42000000,
0x43000000, or anywhere as long as such region is not used by others.
So, the "ranges" is just one possible software configuration, which
does not seem to fit in device tree because device tree is a hardware
description language.  However, of_translate_address() requires
"ranges" in every bus node between CPUs and device mapped on the CPU
address space.  In other words, "ranges" properties must be statically
defined in device tree.  After some discussion, I decided the dynamic
address reassignment by the driver is too bothersome.  Instead, the
device tree should provide a reasonable translation setup that the OS
can rely on.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>

Documentation/devicetree/bindings/bus/uniphier-system-bus.txt

@@ -0,0 +1,66 @@
+UniPhier System Bus
+
+The UniPhier System Bus is an external bus that connects on-board devices to
+the UniPhier SoC.  It is a simple (semi-)parallel bus with address, data, and
+some control signals.  It supports up to 8 banks (chip selects).
+
+Before any access to the bus, the bus controller must be configured; the bus
+controller registers provide the control for the translation from the offset
+within each bank to the CPU-viewed address.  The needed setup includes the base
+address, the size of each bank.  Optionally, some timing parameters can be
+optimized for faster bus access.
+
+Required properties:
+- compatible: should be "socionext,uniphier-system-bus".
+- reg: offset and length of the register set for the bus controller device.
+- #address-cells: should be 2.  The first cell is the bank number (chip select).
+  The second cell is the address offset within the bank.
+- #size-cells: should be 1.
+- ranges: should provide a proper address translation from the System Bus to
+  the parent bus.
+
+Note:
+The address region(s) that can be assigned for the System Bus is implementation
+defined.  Some SoCs can use 0x00000000-0x0fffffff and 0x40000000-0x4fffffff,
+while other SoCs can only use 0x40000000-0x4fffffff.  There might be additional
+limitations depending on SoCs and the boot mode.  The address translation is
+arbitrary as long as the banks are assigned in the supported address space with
+the required alignment and they do not overlap one another.
+For example, it is possible to map:
+  bank 0 to 0x42000000-0x43ffffff, bank 5 to 0x46000000-0x46ffffff
+It is also possible to map:
+  bank 0 to 0x48000000-0x49ffffff, bank 5 to 0x44000000-0x44ffffff
+There is no reason to stick to a particular translation mapping, but the
+"ranges" property should provide a "reasonable" default that is known to work.
+The software should initialize the bus controller according to it.
+
+Example:
+
+	system-bus {
+		compatible = "socionext,uniphier-system-bus";
+		reg = <0x58c00000 0x400>;
+		#address-cells = <2>;
+		#size-cells = <1>;
+		ranges = <1 0x00000000 0x42000000 0x02000000
+			  5 0x00000000 0x46000000 0x01000000>;
+
+		ethernet@1,01f00000 {
+			compatible = "smsc,lan9115";
+			reg = <1 0x01f00000 0x1000>;
+			interrupts = <0 48 4>
+			phy-mode = "mii";
+		};
+
+		uart@5,00200000 {
+			compatible = "ns16550a";
+			reg = <5 0x00200000 0x20>;
+			interrupts = <0 49 4>
+			clock-frequency = <12288000>;
+		};
+	};
+
+In this example,
+ - the Ethernet device is connected at the offset 0x01f00000 of CS1 and
+   mapped to 0x43f00000 of the parent bus.
+ - the UART device is connected at the offset 0x00200000 of CS5 and
+   mapped to 0x46200000 of the parent bus.

MAINTAINERS

@@ -1642,6 +1642,7 @@ F:	arch/arm/boot/dts/uniphier*
 F:	arch/arm/include/asm/hardware/cache-uniphier.h
 F:	arch/arm/mach-uniphier/
 F:	arch/arm/mm/cache-uniphier.c
+F:	drivers/bus/uniphier-system-bus.c
 F:	drivers/i2c/busses/i2c-uniphier*
 F:	drivers/pinctrl/uniphier/
 F:	drivers/tty/serial/8250/8250_uniphier.c

drivers/bus/Kconfig

@@ -131,6 +131,14 @@ config SUNXI_RSB
 	  with various RSB based devices, such as AXP223, AXP8XX PMICs,
 	  and AC100/AC200 ICs.
 
+config UNIPHIER_SYSTEM_BUS
+	tristate "UniPhier System Bus driver"
+	depends on ARCH_UNIPHIER && OF
+	default y
+	help
+	  Support for UniPhier System Bus, a simple external bus.  This is
+	  needed to use on-board devices connected to UniPhier SoCs.
+
 config VEXPRESS_CONFIG
 	bool "Versatile Express configuration bus"
 	default y if ARCH_VEXPRESS

drivers/bus/Makefile

@@ -17,4 +17,5 @@ obj-$(CONFIG_OMAP_INTERCONNECT)	+= omap_l3_smx.o omap_l3_noc.o
 obj-$(CONFIG_OMAP_OCP2SCP)	+= omap-ocp2scp.o
 obj-$(CONFIG_SUNXI_RSB)		+= sunxi-rsb.o
 obj-$(CONFIG_SIMPLE_PM_BUS)	+= simple-pm-bus.o
+obj-$(CONFIG_UNIPHIER_SYSTEM_BUS)	+= uniphier-system-bus.o
 obj-$(CONFIG_VEXPRESS_CONFIG)	+= vexpress-config.o

drivers/bus/uniphier-system-bus.c

@@ -0,0 +1,281 @@
+/*
+ * Copyright (C) 2015 Masahiro Yamada <yamada.masahiro@socionext.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/io.h>
+#include <linux/log2.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+
+/* System Bus Controller registers */
+#define UNIPHIER_SBC_BASE	0x100	/* base address of bank0 space */
+#define    UNIPHIER_SBC_BASE_BE		BIT(0)	/* bank_enable */
+#define UNIPHIER_SBC_CTRL0	0x200	/* timing parameter 0 of bank0 */
+#define UNIPHIER_SBC_CTRL1	0x204	/* timing parameter 1 of bank0 */
+#define UNIPHIER_SBC_CTRL2	0x208	/* timing parameter 2 of bank0 */
+#define UNIPHIER_SBC_CTRL3	0x20c	/* timing parameter 3 of bank0 */
+#define UNIPHIER_SBC_CTRL4	0x300	/* timing parameter 4 of bank0 */
+
+#define UNIPHIER_SBC_STRIDE	0x10	/* register stride to next bank */
+#define UNIPHIER_SBC_NR_BANKS	8	/* number of banks (chip select) */
+#define UNIPHIER_SBC_BASE_DUMMY	0xffffffff	/* data to squash bank 0, 1 */
+
+struct uniphier_system_bus_bank {
+	u32 base;
+	u32 end;
+};
+
+struct uniphier_system_bus_priv {
+	struct device *dev;
+	void __iomem *membase;
+	struct uniphier_system_bus_bank bank[UNIPHIER_SBC_NR_BANKS];
+};
+
+static int uniphier_system_bus_add_bank(struct uniphier_system_bus_priv *priv,
+					int bank, u32 addr, u64 paddr, u32 size)
+{
+	u64 end, mask;
+
+	dev_dbg(priv->dev,
+		"range found: bank = %d, addr = %08x, paddr = %08llx, size = %08x\n",
+		bank, addr, paddr, size);
+
+	if (bank >= ARRAY_SIZE(priv->bank)) {
+		dev_err(priv->dev, "unsupported bank number %d\n", bank);
+		return -EINVAL;
+	}
+
+	if (priv->bank[bank].base || priv->bank[bank].end) {
+		dev_err(priv->dev,
+			"range for bank %d has already been specified\n", bank);
+		return -EINVAL;
+	}
+
+	if (paddr > U32_MAX) {
+		dev_err(priv->dev, "base address %llx is too high\n", paddr);
+		return -EINVAL;
+	}
+
+	end = paddr + size;
+
+	if (addr > paddr) {
+		dev_err(priv->dev,
+			"base %08x cannot be mapped to %08llx of parent\n",
+			addr, paddr);
+		return -EINVAL;
+	}
+	paddr -= addr;
+
+	paddr = round_down(paddr, 0x00020000);
+	end = round_up(end, 0x00020000);
+
+	if (end > U32_MAX) {
+		dev_err(priv->dev, "end address %08llx is too high\n", end);
+		return -EINVAL;
+	}
+	mask = paddr ^ (end - 1);
+	mask = roundup_pow_of_two(mask);
+
+	paddr = round_down(paddr, mask);
+	end = round_up(end, mask);
+
+	priv->bank[bank].base = paddr;
+	priv->bank[bank].end = end;
+
+	dev_dbg(priv->dev, "range added: bank = %d, addr = %08x, end = %08x\n",
+		bank, priv->bank[bank].base, priv->bank[bank].end);
+
+	return 0;
+}
+
+static int uniphier_system_bus_check_overlap(
+				const struct uniphier_system_bus_priv *priv)
+{
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(priv->bank); i++) {
+		for (j = i + 1; j < ARRAY_SIZE(priv->bank); j++) {
+			if (priv->bank[i].end > priv->bank[j].base ||
+			    priv->bank[i].base < priv->bank[j].end) {
+				dev_err(priv->dev,
+					"region overlap between bank%d and bank%d\n",
+					i, j);
+				return -EINVAL;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static void uniphier_system_bus_check_boot_swap(
+					struct uniphier_system_bus_priv *priv)
+{
+	void __iomem *base_reg = priv->membase + UNIPHIER_SBC_BASE;
+	int is_swapped;
+
+	is_swapped = !(readl(base_reg) & UNIPHIER_SBC_BASE_BE);
+
+	dev_dbg(priv->dev, "Boot Swap: %s\n", is_swapped ? "on" : "off");
+
+	/*
+	 * If BOOT_SWAP was asserted on power-on-reset, the CS0 and CS1 are
+	 * swapped.  In this case, bank0 and bank1 should be swapped as well.
+	 */
+	if (is_swapped)
+		swap(priv->bank[0], priv->bank[1]);
+}
+
+static void uniphier_system_bus_set_reg(
+				const struct uniphier_system_bus_priv *priv)
+{
+	void __iomem *base_reg = priv->membase + UNIPHIER_SBC_BASE;
+	u32 base, end, mask, val;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(priv->bank); i++) {
+		base = priv->bank[i].base;
+		end = priv->bank[i].end;
+
+		if (base == end) {
+			/*
+			 * If SBC_BASE0 or SBC_BASE1 is set to zero, the access
+			 * to anywhere in the system bus space is routed to
+			 * bank 0 (if boot swap if off) or bank 1 (if boot swap
+			 * if on).  It means that CPUs cannot get access to
+			 * bank 2 or later.  In other words, bank 0/1 cannot
+			 * be disabled even if its bank_enable bits is cleared.
+			 * This seems odd, but it is how this hardware goes.
+			 * As a workaround, dummy data (0xffffffff) should be
+			 * set when the bank 0/1 is unused.  As for bank 2 and
+			 * later, they can be simply disable by clearing the
+			 * bank_enable bit.
+			 */
+			if (i < 2)
+				val = UNIPHIER_SBC_BASE_DUMMY;
+			else
+				val = 0;
+		} else {
+			mask = base ^ (end - 1);
+
+			val = base & 0xfffe0000;
+			val |= (~mask >> 16) & 0xfffe;
+			val |= UNIPHIER_SBC_BASE_BE;
+		}
+		dev_dbg(priv->dev, "SBC_BASE[%d] = 0x%08x\n", i, val);
+
+		writel(val, base_reg + UNIPHIER_SBC_STRIDE * i);
+	}
+}
+
+static int uniphier_system_bus_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct uniphier_system_bus_priv *priv;
+	struct resource *regs;
+	const __be32 *ranges;
+	u32 cells, addr, size;
+	u64 paddr;
+	int pna, bank, rlen, rone, ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	regs = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	priv->membase = devm_ioremap_resource(dev, regs);
+	if (IS_ERR(priv->membase))
+		return PTR_ERR(priv->membase);
+
+	priv->dev = dev;
+
+	pna = of_n_addr_cells(dev->of_node);
+
+	ret = of_property_read_u32(dev->of_node, "#address-cells", &cells);
+	if (ret) {
+		dev_err(dev, "failed to get #address-cells\n");
+		return ret;
+	}
+	if (cells != 2) {
+		dev_err(dev, "#address-cells must be 2\n");
+		return -EINVAL;
+	}
+
+	ret = of_property_read_u32(dev->of_node, "#size-cells", &cells);
+	if (ret) {
+		dev_err(dev, "failed to get #size-cells\n");
+		return ret;
+	}
+	if (cells != 1) {
+		dev_err(dev, "#size-cells must be 1\n");
+		return -EINVAL;
+	}
+
+	ranges = of_get_property(dev->of_node, "ranges", &rlen);
+	if (!ranges) {
+		dev_err(dev, "failed to get ranges property\n");
+		return -ENOENT;
+	}
+
+	rlen /= sizeof(*ranges);
+	rone = pna + 2;
+
+	for (; rlen >= rone; rlen -= rone) {
+		bank = be32_to_cpup(ranges++);
+		addr = be32_to_cpup(ranges++);
+		paddr = of_translate_address(dev->of_node, ranges);
+		if (paddr == OF_BAD_ADDR)
+			return -EINVAL;
+		ranges += pna;
+		size = be32_to_cpup(ranges++);
+
+		ret = uniphier_system_bus_add_bank(priv, bank, addr,
+						   paddr, size);
+		if (ret)
+			return ret;
+	}
+
+	ret = uniphier_system_bus_check_overlap(priv);
+	if (ret)
+		return ret;
+
+	uniphier_system_bus_check_boot_swap(priv);
+
+	uniphier_system_bus_set_reg(priv);
+
+	/* Now, the bus is configured.  Populate platform_devices below it */
+	return of_platform_populate(dev->of_node, of_default_bus_match_table,
+				    NULL, dev);
+}
+
+static const struct of_device_id uniphier_system_bus_match[] = {
+	{ .compatible = "socionext,uniphier-system-bus" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, uniphier_system_bus_match);
+
+static struct platform_driver uniphier_system_bus_driver = {
+	.probe		= uniphier_system_bus_probe,
+	.driver = {
+		.name	= "uniphier-system-bus",
+		.of_match_table = uniphier_system_bus_match,
+	},
+};
+module_platform_driver(uniphier_system_bus_driver);
+
+MODULE_AUTHOR("Masahiro Yamada <yamada.masahiro@socionext.com>");
+MODULE_DESCRIPTION("UniPhier System Bus driver");
+MODULE_LICENSE("GPL");