[PATCH v5 3/4] remoteproc/MIPS: Add a remoteproc driver for MIPS

[Matt Redfearn]

This driver allows a MIPS processor offlined from Linux to be used as a
remote processor. Firmware may be loaded via the sysfs interface and
changed at runtime, allowing the processor to handle real-time tasks or
perform coprocessing while remaining processors are available to Linux.

Coprocessor firmware must abide by the remoteproc standard, i.e.
implement the resource table containing memory layouts and virtio device
descriptions, and additionally abide by the MIPS UHI coprocessor boot
protocol in the startup code.

Signed-off-by: Lisa Parratt <lisa.parratt@xxxxxxxxxx>
Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxxxx>

---

Changes in v5:
Depend on !64bit since this driver only works with 32bit kernels
Set mproc->tsk state to TASK_DEAD before freeing it to avoid warning
Flush icache of each carveout so that icache sees latest data written

Changes in v4:
Have a single mips-rproc device to be parent to each CPU's rproc device.
Support per-device coherence introduced in v4.9
Add a sysfs interface to control the mask of cpus available to rproc

Changes in v3:
Update MIPS remoteproc driver to use CPU hotplug state machine
Remove sysfs interface from MIPS rproc driver, now provided by the core.
Drop patches that Ralf has already merged to mips-next

Changes in v2: None

 Documentation/ABI/testing/sysfs-devices-mips-rproc |  13 +
 drivers/remoteproc/Kconfig                         |  11 +
 drivers/remoteproc/Makefile                        |   1 +
 drivers/remoteproc/mips_remoteproc.c               | 596 +++++++++++++++++++++
 4 files changed, 621 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-devices-mips-rproc
 create mode 100644 drivers/remoteproc/mips_remoteproc.c

diff --git a/Documentation/ABI/testing/sysfs-devices-mips-rproc b/Documentation/ABI/testing/sysfs-devices-mips-rproc
new file mode 100644
index 000000000000..b06f6671807a
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-mips-rproc
@@ -0,0 +1,13 @@
+What:		/sys/devices/mips-rproc/cpus
+Date:		October 2016
+Contact:	Matt Redfearn <matt.redfearn@xxxxxxxxxx>
+Description:
+		CPU topology file describing which CPUs may be used by the
+		MIPS remote processor driver when offline from Linux.
+
+		This can be read to observe the current setting, or written to
+		change the allowed CPUs.
+
+		The format is compatible with cpulist_parse()
+		[see <linux/cpumask.h>], for example to enable the MIPS remote
+		processor driver on CPUs 1,2 & 3, write "1-3" into this file.
diff --git a/drivers/remoteproc/Kconfig b/drivers/remoteproc/Kconfig
index 8f9cf0bc571c..3be2202f639d 100644
--- a/drivers/remoteproc/Kconfig
+++ b/drivers/remoteproc/Kconfig
@@ -68,6 +68,17 @@ config DA8XX_REMOTEPROC
 	  It's safe to say n here if you're not interested in multimedia
 	  offloading.
 
+config MIPS_REMOTEPROC
+	tristate "MIPS remoteproc support"
+	depends on MIPS_CPS && HAS_DMA && !64BIT
+	depends on REMOTEPROC
+	select CMA
+	select MIPS_CPU_STEAL
+	help
+	  Say y here to support using offline cores/VPEs as remote processors
+	  via the remote processor framework.
+	  If unsure say N.
+
 config QCOM_ADSP_PIL
 	tristate "Qualcomm ADSP Peripheral Image Loader"
 	depends on OF && ARCH_QCOM
diff --git a/drivers/remoteproc/Makefile b/drivers/remoteproc/Makefile
index 0938ea3c41ba..580ee8907da9 100644
--- a/drivers/remoteproc/Makefile
+++ b/drivers/remoteproc/Makefile
@@ -11,6 +11,7 @@ remoteproc-y				+= remoteproc_elf_loader.o
 obj-$(CONFIG_OMAP_REMOTEPROC)		+= omap_remoteproc.o
 obj-$(CONFIG_WKUP_M3_RPROC)		+= wkup_m3_rproc.o
 obj-$(CONFIG_DA8XX_REMOTEPROC)		+= da8xx_remoteproc.o
+obj-$(CONFIG_MIPS_REMOTEPROC)		+= mips_remoteproc.o
 obj-$(CONFIG_QCOM_ADSP_PIL)		+= qcom_adsp_pil.o
 obj-$(CONFIG_QCOM_MDT_LOADER)		+= qcom_mdt_loader.o
 obj-$(CONFIG_QCOM_Q6V5_PIL)		+= qcom_q6v5_pil.o
diff --git a/drivers/remoteproc/mips_remoteproc.c b/drivers/remoteproc/mips_remoteproc.c
new file mode 100644
index 000000000000..9a2a7bbddc0a
--- /dev/null
+++ b/drivers/remoteproc/mips_remoteproc.c
@@ -0,0 +1,596 @@
+/*
+ * MIPS Remote Processor driver
+ *
+ * Copyright (C) 2016 Imagination Technologies
+ * Lisa Parratt <lisa.parratt@xxxxxxxxxx>
+ * Matt Redfearn <matt.redfearn@xxxxxxxxxx>
+ *
+ * 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.
+ */
+
+#include <linux/cpu.h>
+#include <linux/dma-mapping.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/irq.h>
+#include <linux/module.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/remoteproc.h>
+
+#include <asm/cacheflush.h>
+#include <asm/smp-cps.h>
+#include <asm/tlbflush.h>
+#include <asm/tlbmisc.h>
+
+#include "remoteproc_internal.h"
+
+struct mips_rproc {
+	char			name[16];
+	struct rproc		*rproc;
+	struct task_struct	*tsk;
+	unsigned int		cpu;
+	int			ipi_linux;
+	int			ipi_remote;
+};
+
+/* Parent device for MIPS remoteproc */
+static struct device mips_rproc_dev;
+
+/* Array of allocated MIPS remote processor instances */
+static struct mips_rproc *mips_rprocs[NR_CPUS];
+
+/* Bitmap used to identify which CPUs are available to rproc */
+static cpumask_var_t mips_rproc_cpumask;
+
+/* Dynamic CPU hotplug state associated with this driver */
+static int cpuhp_state;
+
+/* Add wired entry to map a device address to physical memory */
+static void mips_map_page(unsigned long da, unsigned long pa, int c,
+			  unsigned long pagesize)
+{
+	unsigned long pa2 = pa + (pagesize / 2);
+	unsigned long entryhi, entrylo0, entrylo1;
+	unsigned long pagemask = pagesize - 0x2000;
+
+	pa = (pa >> 6) & (ULONG_MAX << MIPS_ENTRYLO_PFN_SHIFT);
+	pa2 = (pa2 >> 6) & (ULONG_MAX << MIPS_ENTRYLO_PFN_SHIFT);
+	entryhi = da & 0xfffffe000;
+	entrylo0 = (c << ENTRYLO_C_SHIFT) | ENTRYLO_D | ENTRYLO_V | pa;
+	entrylo1 = (c << ENTRYLO_C_SHIFT) | ENTRYLO_D | ENTRYLO_V | pa2;
+
+	pr_debug("Create wired entry %d, CCA %d\n", read_c0_wired(), c);
+	pr_debug(" EntryHi: 0x%016lx\n", entryhi);
+	pr_debug(" EntryLo0: 0x%016lx\n", entrylo0);
+	pr_debug(" EntryLo1: 0x%016lx\n", entrylo1);
+	pr_debug(" Pagemask: 0x%016lx\n", pagemask);
+	pr_debug("\n");
+
+	add_wired_entry(entrylo0, entrylo1, entryhi, pagemask);
+}
+
+/* Compute the largest page mask a physical address can be mapped with */
+static unsigned long mips_rproc_largest_pm(unsigned long pa,
+					   unsigned long maxmask)
+{
+	unsigned long mask;
+	/* Find address bits limiting alignment */
+	unsigned long shift = ffs(pa);
+
+	/* Obey MIPS restrictions on page sizes */
+	if (pa) {
+		if (shift & 1)
+			shift -= 2;
+		else
+			shift--;
+	}
+	mask = ULONG_MAX << shift;
+	return maxmask & ~mask;
+}
+
+/* Compute the page mask one step larger than a given page mask */
+static unsigned long mips_rproc_next_pm(unsigned long pm, unsigned long maxmask)
+{
+#define PM_SHIFT 13
+	return ((pm << 2) | (0x3 << PM_SHIFT)) & maxmask;
+}
+
+/*
+ * Add mappings to the TLB such that memory allocated by the kernel for a
+ * firmware component appears at the right virtual address
+ */
+static inline void mips_rproc_map(unsigned long da, unsigned long pa, int c,
+				  unsigned long size, unsigned long maxmask)
+{
+	/* minimum mappable size is 2 * 4k pages */
+	const unsigned long min_map_sz = 0x2000;
+	unsigned long bigmask, nextmask;
+	unsigned long distance, target;
+	unsigned long page2_size; /* Size of the 2 buddy pages */
+
+	do {
+		/* Compute the current largest page mask */
+		bigmask = mips_rproc_largest_pm(pa, maxmask);
+		/* Compute the next largest pagesize */
+		nextmask = mips_rproc_next_pm(bigmask, maxmask);
+		/*
+		 * Compute the distance from our current physical address to
+		 * the next page boundary.
+		 */
+		distance = (nextmask + min_map_sz) - (pa & nextmask);
+		/*
+		 * Decide between searching to get to the next highest page
+		 * boundary or finishing.
+		 */
+		target = distance < size ? distance : size;
+		while (target) {
+			/* Find the largest supported page size that will fit */
+			for (page2_size = maxmask + min_map_sz;
+			    (page2_size > min_map_sz) && (page2_size > target);
+			     page2_size /= 4) {
+			}
+			/* Emit it */
+			mips_map_page(da, pa, c, page2_size);
+			/* Move to next step */
+			size -= page2_size;
+			da += page2_size;
+			pa += page2_size;
+			target -= page2_size;
+		}
+	} while (size);
+}
+
+static int mips_rproc_carveouts(struct rproc *rproc, int max_pagemask)
+{
+	struct rproc_mem_entry *carveout;
+
+	list_for_each_entry(carveout, &rproc->carveouts, node) {
+		int c = CONF_CM_CACHABLE_COW;
+
+		dev_dbg(&rproc->dev,
+			"carveout mapping da 0x%x -> %pad length 0x%x, CCA %d",
+			carveout->da, &carveout->dma, carveout->len, c);
+
+		mips_rproc_map(carveout->da, carveout->dma, c,
+				carveout->len, max_pagemask);
+		flush_icache_range((unsigned long)carveout->va,
+				   (unsigned long)carveout->va + carveout->len);
+	}
+	return 0;
+}
+
+static int mips_rproc_vdevs(struct rproc *rproc, int max_pagemask)
+{
+	struct rproc_vdev *rvdev;
+
+	list_for_each_entry(rvdev, &rproc->rvdevs, node) {
+		int i, size;
+
+		for (i = 0; i < ARRAY_SIZE(rvdev->vring); i++) {
+			struct rproc_vring *vring = &rvdev->vring[i];
+			unsigned long pa = vring->dma;
+			int c;
+
+			if (plat_device_is_coherent(&mips_rproc_dev)) {
+				/*
+				 * The DMA API will allocate cacheable buffers
+				 * for shared resources, so the firmware should
+				 * also access those buffers cached
+				 */
+				c = (_page_cachable_default >> _CACHE_SHIFT);
+			} else {
+				/*
+				 * Otherwise, shared buffers should be accessed
+				 * uncached
+				 */
+				c = CONF_CM_UNCACHED;
+			}
+
+			/* actual size of vring (in bytes) */
+			size = PAGE_ALIGN(vring_size(vring->len, vring->align));
+
+			dev_dbg(&rproc->dev,
+				"vring mapping da %pad -> %pad length 0x%x, CCA %d",
+				&vring->dma, &vring->dma, size, c);
+
+			mips_rproc_map(pa, pa, c, size, max_pagemask);
+		}
+	}
+	return 0;
+}
+
+static void mips_rproc_cpu_entry(void)
+{
+	struct mips_rproc *mproc = mips_rprocs[smp_processor_id()];
+	struct rproc *rproc = mproc->rproc;
+	int ipi_to_remote = ipi_get_hwirq(mproc->ipi_remote, mproc->cpu);
+	int ipi_from_remote = ipi_get_hwirq(mproc->ipi_linux, 0);
+	unsigned long old_pagemask, max_pagemask;
+	void (*fw_entry)(int, int ipi_to_remote, int ipi_from_remote, int);
+
+	dev_info(&rproc->dev, "%s booting firmware %s\n",
+		 rproc->name, rproc->firmware);
+
+	/* Get the maximum pagemask supported on this CPU */
+	old_pagemask = read_c0_pagemask();
+	write_c0_pagemask(~0);
+	back_to_back_c0_hazard();
+	max_pagemask = read_c0_pagemask();
+	write_c0_pagemask(old_pagemask);
+	back_to_back_c0_hazard();
+
+	/* Start with no wired entries */
+	write_c0_wired(0);
+
+	/* Flush all previous TLB entries */
+	local_flush_tlb_all();
+
+	/* Set ASID 0 */
+	write_c0_entryhi(0);
+
+	/* Map firmware resources into virtual memory */
+	mips_rproc_carveouts(rproc, max_pagemask);
+	mips_rproc_vdevs(rproc, max_pagemask);
+
+	dev_dbg(&rproc->dev, "IPI to remote: %d\n", ipi_to_remote);
+	dev_dbg(&rproc->dev, "IPI from remote: %d\n", ipi_from_remote);
+
+	/* Hand off the CPU to the firmware */
+	dev_dbg(&rproc->dev, "Jumping to firmware at 0x%x\n", rproc->bootaddr);
+
+	/* Jump into the firmware, obeying the firmware protocol. */
+	fw_entry = (void *)rproc->bootaddr;
+	fw_entry(-3, ipi_to_remote, ipi_from_remote, 0);
+}
+
+static irqreturn_t mips_rproc_ipi_handler(int irq, void *dev_id)
+{
+	/* Synthetic interrupts shouldn't need acking */
+	return IRQ_WAKE_THREAD;
+}
+
+static irqreturn_t mips_rproc_vq_int(int irq, void *p)
+{
+	struct rproc *rproc = (struct rproc *)p;
+	void *entry;
+	int id;
+
+	/* We don't have a mailbox, so iterate over all vqs and kick them. */
+	idr_for_each_entry(&rproc->notifyids, entry, id)
+		rproc_vq_interrupt(rproc, id);
+
+	return IRQ_HANDLED;
+}
+
+/* Helper function to find the IPI domain */
+static struct irq_domain *ipi_domain(void)
+{
+	struct device_node *node = of_irq_find_parent(of_root);
+	struct irq_domain *ipidomain;
+
+	ipidomain = irq_find_matching_host(node, DOMAIN_BUS_IPI);
+	/*
+	 * Some platforms have half DT setup. So if we found irq node but
+	 * didn't find an ipidomain, try to search for one that is not in the
+	 * DT.
+	 */
+	if (node && !ipidomain)
+		ipidomain = irq_find_matching_host(NULL, DOMAIN_BUS_IPI);
+
+	return ipidomain;
+}
+
+int mips_rproc_op_start(struct rproc *rproc)
+{
+	struct mips_rproc *mproc = rproc->priv;
+	int err;
+	int cpu = mproc->cpu;
+
+	/* Create task for the CPU to use before handing off to firmware */
+	mproc->tsk = fork_idle(cpu);
+	if (IS_ERR(mproc->tsk)) {
+		dev_err(&rproc->dev, "fork_idle() failed for CPU%d\n", cpu);
+		return -ENOMEM;
+	}
+
+	/* We won't be needing the Linux IPIs anymore */
+	if (mips_smp_ipi_free(get_cpu_mask(cpu))) {
+		dev_err(&rproc->dev, "Failed to reserve incoming kick\n");
+		goto exit_free_tsk;
+	}
+
+	/*
+	 * Direct IPIs from the remote processor to CPU0 since that can't be
+	 * offlined while the remote CPU is running.
+	 */
+	mproc->ipi_linux = irq_reserve_ipi(ipi_domain(), get_cpu_mask(0));
+	if (!mproc->ipi_linux) {
+		dev_err(&rproc->dev, "Failed to reserve incoming kick\n");
+		goto exit_restore_ipi;
+	}
+
+	mproc->ipi_remote = irq_reserve_ipi(ipi_domain(), get_cpu_mask(cpu));
+	if (!mproc->ipi_remote) {
+		dev_err(&rproc->dev, "Failed to reserve outgoing kick\n");
+		goto exit_destroy_ipi_linux;
+	}
+
+	/* register incoming ipi */
+	err = request_threaded_irq(mproc->ipi_linux, mips_rproc_ipi_handler,
+				   mips_rproc_vq_int, 0,
+				   "mips-rproc IPI in", rproc);
+	if (err) {
+		dev_err(&rproc->dev, "Failed to register incoming kick: %d\n",
+			err);
+		goto exit_destroy_ipi_remote;
+	}
+
+	if (mips_cps_steal_cpu_and_execute(cpu, &mips_rproc_cpu_entry,
+						mproc->tsk)) {
+		dev_err(&rproc->dev, "Failed to steal CPU%d for remote\n", cpu);
+		goto exit_free_irq;
+	}
+
+	return 0;
+
+exit_free_irq:
+	free_irq(mproc->ipi_linux, rproc);
+exit_destroy_ipi_remote:
+	irq_destroy_ipi(mproc->ipi_remote, get_cpu_mask(cpu));
+exit_destroy_ipi_linux:
+	irq_destroy_ipi(mproc->ipi_linux, get_cpu_mask(0));
+exit_restore_ipi:
+	/* Set up the Linux IPIs again */
+	mips_smp_ipi_allocate(get_cpu_mask(cpu));
+exit_free_tsk:
+	free_task(mproc->tsk);
+
+	return -EINVAL;
+}
+
+int mips_rproc_op_stop(struct rproc *rproc)
+{
+	struct mips_rproc *mproc = rproc->priv;
+
+	free_irq(mproc->ipi_linux, rproc);
+
+	irq_destroy_ipi(mproc->ipi_linux, get_cpu_mask(0));
+	irq_destroy_ipi(mproc->ipi_remote, get_cpu_mask(mproc->cpu));
+
+	/* Set up the Linux IPIs again */
+	mips_smp_ipi_allocate(get_cpu_mask(mproc->cpu));
+
+	set_task_state(mproc->tsk, TASK_DEAD);
+	free_task(mproc->tsk);
+
+	return mips_cps_halt_and_return_cpu(mproc->cpu);
+}
+
+void mips_rproc_op_kick(struct rproc *rproc, int vqid)
+{
+	struct mips_rproc *mproc = rproc->priv;
+
+	if (rproc->state == RPROC_RUNNING)
+		ipi_send_single(mproc->ipi_remote, mproc->cpu);
+}
+
+static const struct rproc_ops mips_rproc_proc_ops = {
+	.start	= mips_rproc_op_start,
+	.stop	= mips_rproc_op_stop,
+	.kick	= mips_rproc_op_kick,
+};
+
+/* Create an rproc instance in response to CPU down */
+static int mips_rproc_device_register(unsigned int cpu)
+{
+	char *template = "mips-cpu%u";
+	struct rproc *rproc;
+	struct mips_rproc *mproc;
+	int err;
+
+	if (!cpumask_test_cpu(cpu, mips_rproc_cpumask))
+		/* The CPU is not in the mask, so don't register rproc on it */
+		return 0;
+
+	pr_debug("Allocating MIPS rproc for cpu%d\n", cpu);
+
+	if (mips_rprocs[cpu]) {
+		dev_err(&mips_rproc_dev, "CPU%d in use\n", cpu);
+		return 0;
+	}
+
+	mproc = kzalloc(sizeof(struct mips_rproc), GFP_KERNEL);
+	if (!mproc) {
+		err = -ENOMEM;
+		goto exit;
+	}
+
+	snprintf(mproc->name, sizeof(mproc->name), template, cpu);
+	mproc->cpu = cpu;
+
+	rproc = rproc_alloc(&mips_rproc_dev, mproc->name,
+			    &mips_rproc_proc_ops, NULL,
+			    sizeof(struct mips_rproc *));
+	if (!rproc) {
+		dev_err(&mips_rproc_dev, "Error allocating rproc\n");
+		err = -ENOMEM;
+		goto exit_free_mproc;
+	}
+
+	mproc->rproc = rproc;
+	rproc->priv = (void *)mproc;
+
+	err = rproc_add(rproc);
+	if (err) {
+		dev_err(&mips_rproc_dev, "Failed to add rproc: %d\n", err);
+		goto exit_free_rproc;
+	}
+
+	mips_rprocs[cpu] = mproc;
+	return 0;
+
+exit_free_rproc:
+	rproc_free(rproc);
+exit_free_mproc:
+	kfree(mproc);
+exit:
+	return err;
+}
+
+/* Destroy rproc instance in response to CPU up */
+static int mips_rproc_device_unregister(unsigned int cpu)
+{
+	struct mips_rproc *mproc = mips_rprocs[cpu];
+
+	if (!mproc)
+		/* No rproc instance has been created for this CPU */
+		return 0;
+
+	pr_debug("Deallocating MIPS rproc for cpu%d\n", cpu);
+
+	rproc_del(mproc->rproc);
+	rproc_put(mproc->rproc);
+	kfree(mproc);
+
+	mips_rprocs[cpu] = NULL;
+	return 0;
+}
+
+/* Show MIPS CPUs available to rproc */
+static ssize_t cpus_show(struct device *dev, struct device_attribute *attr,
+			  char *buf)
+{
+	return cpumap_print_to_pagebuf(true, buf, mips_rproc_cpumask);
+}
+
+/* Allow MIPS CPUs to be made available to rproc */
+static ssize_t cpus_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	static cpumask_var_t new_mask;
+	int err, cpu;
+
+	err = cpulist_parse(buf, new_mask);
+	if (err)
+		return err;
+
+	/* Prevent CPU hotplug on/offlining CPUs while we do this */
+	get_online_cpus();
+
+	for_each_possible_cpu(cpu) {
+		if (cpumask_test_cpu(cpu, mips_rproc_cpumask) &&
+		    !cpumask_test_cpu(cpu, new_mask)) {
+			/* CPU no longer allowed. Release any instance on it */
+			cpumask_clear_cpu(cpu, mips_rproc_cpumask);
+			mips_rproc_device_unregister(cpu);
+
+		} else if (!cpumask_test_cpu(cpu, mips_rproc_cpumask) &&
+			   cpumask_test_cpu(cpu, new_mask)) {
+			/* If the CPU isn't online, start an instance */
+			cpumask_set_cpu(cpu, mips_rproc_cpumask);
+			if (!cpu_online(cpu))
+				mips_rproc_device_register(cpu);
+		}
+	}
+	put_online_cpus();
+	return count;
+}
+static DEVICE_ATTR_RW(cpus);
+
+static struct attribute *mips_rproc_attrs[] = {
+	&dev_attr_cpus.attr,
+	NULL
+};
+
+static const struct attribute_group mips_rproc_devgroup = {
+	.attrs = mips_rproc_attrs
+};
+
+static const struct attribute_group *mips_rproc_devgroups[] = {
+	&mips_rproc_devgroup,
+	NULL
+};
+static struct device_type mips_rproc_type = {
+	.groups = mips_rproc_devgroups,
+};
+
+static struct platform_driver mips_rproc_driver = {
+	.driver = {
+		.name = "mips-rproc",
+	},
+};
+
+static int __init mips_rproc_init(void)
+{
+	int err;
+
+	if ((!cpu_has_mipsmt) && (!cpu_has_vp)) {
+		pr_debug("MIPS rproc not supported on this cpu\n");
+		return -EIO;
+	}
+
+	mips_rproc_dev.driver = &mips_rproc_driver.driver;
+	mips_rproc_dev.type = &mips_rproc_type;
+	dev_set_name(&mips_rproc_dev, "mips-rproc");
+
+	/* Set device to have coherent DMA ops */
+	arch_setup_dma_ops(&mips_rproc_dev, 0, 0, NULL, 1);
+
+	err = device_register(&mips_rproc_dev);
+	if (err) {
+		dev_err(&mips_rproc_dev, "Error adding MIPS rproc: %d\n", err);
+		return err;
+	}
+
+	/*
+	 * Register with the cpu hotplug state machine.
+	 * This driver requires opposite sense to "normal" drivers, since the
+	 * driver is activated for offline CPUs via the teardown callback and
+	 * deactivated via the online callback.
+	 */
+	err = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "MIPS:REMOTEPROC",
+				mips_rproc_device_unregister,
+				mips_rproc_device_register);
+	if (err < 0) {
+		device_unregister(&mips_rproc_dev);
+		return err;
+	}
+
+	cpuhp_state = err;
+
+	return 0;
+}
+
+static void __exit mips_rproc_exit(void)
+{
+	int cpu;
+
+	if (cpuhp_state) {
+		/*
+		 * Unregister with the cpu hotplug state machine, but don't call
+		 * the teardown callback, since that would try to start the
+		 * remote processor device.
+		 */
+		__cpuhp_remove_state(cpuhp_state, false);
+		cpuhp_state = 0;
+	}
+
+	get_online_cpus();
+	/* Unregister devices created for any offline CPUs */
+	for_each_possible_cpu(cpu)
+		mips_rproc_device_unregister(cpu);
+	put_online_cpus();
+}
+
+late_initcall(mips_rproc_init);
+module_exit(mips_rproc_exit);
+
+module_platform_driver(mips_rproc_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("MIPS Remote Processor control driver");
-- 
2.7.4