irqchip: add initial support for ompic

IPI driver for the Open Multi-Processor Interrupt Controller (ompic) as
described in the Multi-core support section of the OpenRISC 1.2
architecture specification:

  https://github.com/openrisc/doc/raw/master/openrisc-arch-1.2-rev0.pdf

Each OpenRISC core contains a full interrupt controller which is used in
the SMP architecture for interrupt balancing.  This IPI device, the
ompic, is the only external device required for enabling SMP on
OpenRISC.

Pending ops are stored in a memory bit mask which can allow multiple
pending operations to be set and serviced at a time. This is mostly
borrowed from the alpha IPI implementation.
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
[shorne@gmail.com: converted ops to bitmask, wrote commit message]
Signed-off-by: Stafford Horne <shorne@gmail.com>

Documentation/devicetree/bindings/interrupt-controller/openrisc,ompic.txt

+Open Multi-Processor Interrupt Controller
+
+Required properties:
+
+- compatible : This should be "openrisc,ompic"
+- reg : Specifies base physical address and size of the register space. The
+  size is based on the number of cores the controller has been configured
+  to handle, this should be set to 8 bytes per cpu core.
+- interrupt-controller : Identifies the node as an interrupt controller.
+- #interrupt-cells : This should be set to 0 as this will not be an irq
+  parent.
+- interrupts : Specifies the interrupt line to which the ompic is wired.
+
+Example:
+
+ompic: interrupt-controller@98000000 {
+	compatible = "openrisc,ompic";
+	reg = <0x98000000 16>;
+	interrupt-controller;
+	#interrupt-cells = <0>;
+	interrupts = <1>;
+};

MAINTAINERS

@@ -10034,6 +10034,7 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/openrisc/
 F:	Documentation/openrisc/
 F:	arch/openrisc/
+F:	drivers/irqchip/irq-ompic.c
 F:	drivers/irqchip/irq-or1k-*
 
 OPENVSWITCH

arch/openrisc/Kconfig

@@ -30,6 +30,7 @@ config OPENRISC
 	select NO_BOOTMEM
 	select ARCH_USE_QUEUED_SPINLOCKS
 	select ARCH_USE_QUEUED_RWLOCKS
+	select OMPIC if SMP
 
 config CPU_BIG_ENDIAN
 	def_bool y

drivers/irqchip/Kconfig

@@ -151,6 +151,9 @@ config CLPS711X_IRQCHIP
 	select SPARSE_IRQ
 	default y
 
+config OMPIC
+	bool
+
 config OR1K_PIC
 	bool
 	select IRQ_DOMAIN

drivers/irqchip/Makefile

@@ -17,6 +17,7 @@ obj-$(CONFIG_DW_APB_ICTL)		+= irq-dw-apb-ictl.o
 obj-$(CONFIG_METAG)			+= irq-metag-ext.o
 obj-$(CONFIG_METAG_PERFCOUNTER_IRQS)	+= irq-metag.o
 obj-$(CONFIG_CLPS711X_IRQCHIP)		+= irq-clps711x.o
+obj-$(CONFIG_OMPIC)			+= irq-ompic.o
 obj-$(CONFIG_OR1K_PIC)			+= irq-or1k-pic.o
 obj-$(CONFIG_ORION_IRQCHIP)		+= irq-orion.o
 obj-$(CONFIG_OMAP_IRQCHIP)		+= irq-omap-intc.o

drivers/irqchip/irq-ompic.c

+/*
+ * Open Multi-Processor Interrupt Controller driver
+ *
+ * Copyright (C) 2014 Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
+ * Copyright (C) 2017 Stafford Horne <shorne@gmail.com>
+ *
+ * This file is licensed under the terms of the GNU General Public License
+ * version 2.  This program is licensed "as is" without any warranty of any
+ * kind, whether express or implied.
+ *
+ * The ompic device handles IPI communication between cores in multi-core
+ * OpenRISC systems.
+ *
+ * Registers
+ *
+ * For each CPU the ompic has 2 registers. The control register for sending
+ * and acking IPIs and the status register for receiving IPIs. The register
+ * layouts are as follows:
+ *
+ *  Control register
+ *  +---------+---------+----------+---------+
+ *  | 31      | 30      | 29 .. 16 | 15 .. 0 |
+ *  ----------+---------+----------+----------
+ *  | IRQ ACK | IRQ GEN | DST CORE | DATA    |
+ *  +---------+---------+----------+---------+
+ *
+ *  Status register
+ *  +----------+-------------+----------+---------+
+ *  | 31       | 30          | 29 .. 16 | 15 .. 0 |
+ *  -----------+-------------+----------+---------+
+ *  | Reserved | IRQ Pending | SRC CORE | DATA    |
+ *  +----------+-------------+----------+---------+
+ *
+ * Architecture
+ *
+ * - The ompic generates a level interrupt to the CPU PIC when a message is
+ *   ready.  Messages are delivered via the memory bus.
+ * - The ompic does not have any interrupt input lines.
+ * - The ompic is wired to the same irq line on each core.
+ * - Devices are wired to the same irq line on each core.
+ *
+ *   +---------+                         +---------+
+ *   | CPU     |                         | CPU     |
+ *   |  Core 0 |<==\ (memory access) /==>|  Core 1 |
+ *   |  [ PIC ]|   |                 |   |  [ PIC ]|
+ *   +----^-^--+   |                 |   +----^-^--+
+ *        | |      v                 v        | |
+ *   <====|=|=================================|=|==> (memory bus)
+ *        | |      ^                  ^       | |
+ *  (ipi  | +------|---------+--------|-------|-+ (device irq)
+ *   irq  |        |         |        |       |
+ *  core0)| +------|---------|--------|-------+ (ipi irq core1)
+ *        | |      |         |        |
+ *   +----o-o-+    |    +--------+    |
+ *   | ompic  |<===/    | Device |<===/
+ *   |  IPI   |         +--------+
+ *   +--------+*
+ *
+ */
+
+#include <linux/io.h>
+#include <linux/ioport.h>
+#include <linux/interrupt.h>
+#include <linux/smp.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+
+#include <linux/irqchip.h>
+
+#define OMPIC_CPUBYTES		8
+#define OMPIC_CTRL(cpu)		(0x0 + (cpu * OMPIC_CPUBYTES))
+#define OMPIC_STAT(cpu)		(0x4 + (cpu * OMPIC_CPUBYTES))
+
+#define OMPIC_CTRL_IRQ_ACK	(1 << 31)
+#define OMPIC_CTRL_IRQ_GEN	(1 << 30)
+#define OMPIC_CTRL_DST(cpu)	(((cpu) & 0x3fff) << 16)
+
+#define OMPIC_STAT_IRQ_PENDING	(1 << 30)
+
+#define OMPIC_DATA(x)		((x) & 0xffff)
+
+DEFINE_PER_CPU(unsigned long, ops);
+
+static void __iomem *ompic_base;
+
+static inline u32 ompic_readreg(void __iomem *base, loff_t offset)
+{
+	return ioread32be(base + offset);
+}
+
+static void ompic_writereg(void __iomem *base, loff_t offset, u32 data)
+{
+	iowrite32be(data, base + offset);
+}
+
+static void ompic_raise_softirq(const struct cpumask *mask,
+				unsigned int ipi_msg)
+{
+	unsigned int dst_cpu;
+	unsigned int src_cpu = smp_processor_id();
+
+	for_each_cpu(dst_cpu, mask) {
+		set_bit(ipi_msg, &per_cpu(ops, dst_cpu));
+
+		/*
+		 * On OpenRISC the atomic set_bit() call implies a memory
+		 * barrier.  Otherwise we would need: smp_wmb(); paired
+		 * with the read in ompic_ipi_handler.
+		 */
+
+		ompic_writereg(ompic_base, OMPIC_CTRL(src_cpu),
+			       OMPIC_CTRL_IRQ_GEN |
+			       OMPIC_CTRL_DST(dst_cpu) |
+			       OMPIC_DATA(1));
+	}
+}
+
+static irqreturn_t ompic_ipi_handler(int irq, void *dev_id)
+{
+	unsigned int cpu = smp_processor_id();
+	unsigned long *pending_ops = &per_cpu(ops, cpu);
+	unsigned long ops;
+
+	ompic_writereg(ompic_base, OMPIC_CTRL(cpu), OMPIC_CTRL_IRQ_ACK);
+	while ((ops = xchg(pending_ops, 0)) != 0) {
+
+		/*
+		 * On OpenRISC the atomic xchg() call implies a memory
+		 * barrier.  Otherwise we may need an smp_rmb(); paired
+		 * with the write in ompic_raise_softirq.
+		 */
+
+		do {
+			unsigned long ipi_msg;
+
+			ipi_msg = __ffs(ops);
+			ops &= ~(1UL << ipi_msg);
+
+			handle_IPI(ipi_msg);
+		} while (ops);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int __init ompic_of_init(struct device_node *node,
+				struct device_node *parent)
+{
+	struct resource res;
+	int irq;
+	int ret;
+
+	/* Validate the DT */
+	if (ompic_base) {
+		pr_err("ompic: duplicate ompic's are not supported");
+		return -EEXIST;
+	}
+
+	if (of_address_to_resource(node, 0, &res)) {
+		pr_err("ompic: reg property requires an address and size");
+		return -EINVAL;
+	}
+
+	if (resource_size(&res) < (num_possible_cpus() * OMPIC_CPUBYTES)) {
+		pr_err("ompic: reg size, currently %d must be at least %d",
+			resource_size(&res),
+			(num_possible_cpus() * OMPIC_CPUBYTES));
+		return -EINVAL;
+	}
+
+	/* Setup the device */
+	ompic_base = ioremap(res.start, resource_size(&res));
+	if (IS_ERR(ompic_base)) {
+		pr_err("ompic: unable to map registers");
+		return PTR_ERR(ompic_base);
+	}
+
+	irq = irq_of_parse_and_map(node, 0);
+	if (irq <= 0) {
+		pr_err("ompic: unable to parse device irq");
+		ret = -EINVAL;
+		goto out_unmap;
+	}
+
+	ret = request_irq(irq, ompic_ipi_handler, IRQF_PERCPU,
+				"ompic_ipi", NULL);
+	if (ret)
+		goto out_irq_disp;
+
+	set_smp_cross_call(ompic_raise_softirq);
+
+	return 0;
+
+out_irq_disp:
+	irq_dispose_mapping(irq);
+out_unmap:
+	iounmap(ompic_base);
+	ompic_base = NULL;
+	return ret;
+}
+IRQCHIP_DECLARE(ompic, "openrisc,ompic", ompic_of_init);