Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 698 insertions, 0 deletions

diff --git a/drivers/bus/mips_cdmm.c b/drivers/bus/mips_cdmm.c
new file mode 100644
index 0000000000..554e1992ed
--- /dev/null
+++ b/drivers/bus/mips_cdmm.c
@@ -0,0 +1,698 @@
+/*
+ * Bus driver for MIPS Common Device Memory Map (CDMM).
+ *
+ * Copyright (C) 2014-2015 Imagination Technologies Ltd.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/atomic.h>
+#include <linux/err.h>
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/io.h>
+#include <linux/of_address.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/smp.h>
+#include <asm/cdmm.h>
+#include <asm/hazards.h>
+#include <asm/mipsregs.h>
+
+/* Access control and status register fields */
+#define CDMM_ACSR_DEVTYPE_SHIFT	24
+#define CDMM_ACSR_DEVTYPE	(255ul << CDMM_ACSR_DEVTYPE_SHIFT)
+#define CDMM_ACSR_DEVSIZE_SHIFT	16
+#define CDMM_ACSR_DEVSIZE	(31ul << CDMM_ACSR_DEVSIZE_SHIFT)
+#define CDMM_ACSR_DEVREV_SHIFT	12
+#define CDMM_ACSR_DEVREV	(15ul << CDMM_ACSR_DEVREV_SHIFT)
+#define CDMM_ACSR_UW		(1ul << 3)
+#define CDMM_ACSR_UR		(1ul << 2)
+#define CDMM_ACSR_SW		(1ul << 1)
+#define CDMM_ACSR_SR		(1ul << 0)
+
+/* Each block of device registers is 64 bytes */
+#define CDMM_DRB_SIZE		64
+
+#define to_mips_cdmm_driver(d)	container_of(d, struct mips_cdmm_driver, drv)
+
+/* Default physical base address */
+static phys_addr_t mips_cdmm_default_base;
+
+/* Bus operations */
+
+static const struct mips_cdmm_device_id *
+mips_cdmm_lookup(const struct mips_cdmm_device_id *table,
+		 struct mips_cdmm_device *dev)
+{
+	int ret = 0;
+
+	for (; table->type; ++table) {
+		ret = (dev->type == table->type);
+		if (ret)
+			break;
+	}
+
+	return ret ? table : NULL;
+}
+
+static int mips_cdmm_match(struct device *dev, struct device_driver *drv)
+{
+	struct mips_cdmm_device *cdev = to_mips_cdmm_device(dev);
+	struct mips_cdmm_driver *cdrv = to_mips_cdmm_driver(drv);
+
+	return mips_cdmm_lookup(cdrv->id_table, cdev) != NULL;
+}
+
+static int mips_cdmm_uevent(const struct device *dev, struct kobj_uevent_env *env)
+{
+	const struct mips_cdmm_device *cdev = to_mips_cdmm_device(dev);
+	int retval = 0;
+
+	retval = add_uevent_var(env, "CDMM_CPU=%u", cdev->cpu);
+	if (retval)
+		return retval;
+
+	retval = add_uevent_var(env, "CDMM_TYPE=0x%02x", cdev->type);
+	if (retval)
+		return retval;
+
+	retval = add_uevent_var(env, "CDMM_REV=%u", cdev->rev);
+	if (retval)
+		return retval;
+
+	retval = add_uevent_var(env, "MODALIAS=mipscdmm:t%02X", cdev->type);
+	return retval;
+}
+
+/* Device attributes */
+
+#define CDMM_ATTR(name, fmt, arg...)					\
+static ssize_t name##_show(struct device *_dev,				\
+			   struct device_attribute *attr, char *buf)	\
+{									\
+	struct mips_cdmm_device *dev = to_mips_cdmm_device(_dev);	\
+	return sprintf(buf, fmt, arg);					\
+}									\
+static DEVICE_ATTR_RO(name);
+
+CDMM_ATTR(cpu, "%u\n", dev->cpu);
+CDMM_ATTR(type, "0x%02x\n", dev->type);
+CDMM_ATTR(revision, "%u\n", dev->rev);
+CDMM_ATTR(modalias, "mipscdmm:t%02X\n", dev->type);
+CDMM_ATTR(resource, "\t%016llx\t%016llx\t%016lx\n",
+	  (unsigned long long)dev->res.start,
+	  (unsigned long long)dev->res.end,
+	  dev->res.flags);
+
+static struct attribute *mips_cdmm_dev_attrs[] = {
+	&dev_attr_cpu.attr,
+	&dev_attr_type.attr,
+	&dev_attr_revision.attr,
+	&dev_attr_modalias.attr,
+	&dev_attr_resource.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(mips_cdmm_dev);
+
+struct bus_type mips_cdmm_bustype = {
+	.name		= "cdmm",
+	.dev_groups	= mips_cdmm_dev_groups,
+	.match		= mips_cdmm_match,
+	.uevent		= mips_cdmm_uevent,
+};
+EXPORT_SYMBOL_GPL(mips_cdmm_bustype);
+
+/*
+ * Standard driver callback helpers.
+ *
+ * All the CDMM driver callbacks need to be executed on the appropriate CPU from
+ * workqueues. For the standard driver callbacks we need a work function
+ * (mips_cdmm_{void,int}_work()) to do the actual call from the right CPU, and a
+ * wrapper function (generated with BUILD_PERCPU_HELPER) to arrange for the work
+ * function to be called on that CPU.
+ */
+
+/**
+ * struct mips_cdmm_work_dev - Data for per-device call work.
+ * @fn:		CDMM driver callback function to call for the device.
+ * @dev:	CDMM device to pass to @fn.
+ */
+struct mips_cdmm_work_dev {
+	void			*fn;
+	struct mips_cdmm_device *dev;
+};
+
+/**
+ * mips_cdmm_void_work() - Call a void returning CDMM driver callback.
+ * @data:	struct mips_cdmm_work_dev pointer.
+ *
+ * A work_on_cpu() callback function to call an arbitrary CDMM driver callback
+ * function which doesn't return a value.
+ */
+static long mips_cdmm_void_work(void *data)
+{
+	struct mips_cdmm_work_dev *work = data;
+	void (*fn)(struct mips_cdmm_device *) = work->fn;
+
+	fn(work->dev);
+	return 0;
+}
+
+/**
+ * mips_cdmm_int_work() - Call an int returning CDMM driver callback.
+ * @data:	struct mips_cdmm_work_dev pointer.
+ *
+ * A work_on_cpu() callback function to call an arbitrary CDMM driver callback
+ * function which returns an int.
+ */
+static long mips_cdmm_int_work(void *data)
+{
+	struct mips_cdmm_work_dev *work = data;
+	int (*fn)(struct mips_cdmm_device *) = work->fn;
+
+	return fn(work->dev);
+}
+
+#define _BUILD_RET_void
+#define _BUILD_RET_int	return
+
+/**
+ * BUILD_PERCPU_HELPER() - Helper to call a CDMM driver callback on right CPU.
+ * @_ret:	Return type (void or int).
+ * @_name:	Name of CDMM driver callback function.
+ *
+ * Generates a specific device callback function to call a CDMM driver callback
+ * function on the appropriate CPU for the device, and if applicable return the
+ * result.
+ */
+#define BUILD_PERCPU_HELPER(_ret, _name)				\
+static _ret mips_cdmm_##_name(struct device *dev)			\
+{									\
+	struct mips_cdmm_device *cdev = to_mips_cdmm_device(dev);	\
+	struct mips_cdmm_driver *cdrv = to_mips_cdmm_driver(dev->driver); \
+	struct mips_cdmm_work_dev work = {				\
+		.fn	= cdrv->_name,					\
+		.dev	= cdev,						\
+	};								\
+									\
+	_BUILD_RET_##_ret work_on_cpu(cdev->cpu,			\
+				      mips_cdmm_##_ret##_work, &work);	\
+}
+
+/* Driver callback functions */
+BUILD_PERCPU_HELPER(int, probe)     /* int mips_cdmm_probe(struct device) */
+BUILD_PERCPU_HELPER(int, remove)    /* int mips_cdmm_remove(struct device) */
+BUILD_PERCPU_HELPER(void, shutdown) /* void mips_cdmm_shutdown(struct device) */
+
+
+/* Driver registration */
+
+/**
+ * mips_cdmm_driver_register() - Register a CDMM driver.
+ * @drv:	CDMM driver information.
+ *
+ * Register a CDMM driver with the CDMM subsystem. The driver will be informed
+ * of matching devices which are discovered.
+ *
+ * Returns:	0 on success.
+ */
+int mips_cdmm_driver_register(struct mips_cdmm_driver *drv)
+{
+	drv->drv.bus = &mips_cdmm_bustype;
+
+	if (drv->probe)
+		drv->drv.probe = mips_cdmm_probe;
+	if (drv->remove)
+		drv->drv.remove = mips_cdmm_remove;
+	if (drv->shutdown)
+		drv->drv.shutdown = mips_cdmm_shutdown;
+
+	return driver_register(&drv->drv);
+}
+EXPORT_SYMBOL_GPL(mips_cdmm_driver_register);
+
+/**
+ * mips_cdmm_driver_unregister() - Unregister a CDMM driver.
+ * @drv:	CDMM driver information.
+ *
+ * Unregister a CDMM driver from the CDMM subsystem.
+ */
+void mips_cdmm_driver_unregister(struct mips_cdmm_driver *drv)
+{
+	driver_unregister(&drv->drv);
+}
+EXPORT_SYMBOL_GPL(mips_cdmm_driver_unregister);
+
+
+/* CDMM initialisation and bus discovery */
+
+/**
+ * struct mips_cdmm_bus - Info about CDMM bus.
+ * @phys:		Physical address at which it is mapped.
+ * @regs:		Virtual address where registers can be accessed.
+ * @drbs:		Total number of DRBs.
+ * @drbs_reserved:	Number of DRBs reserved.
+ * @discovered:		Whether the devices on the bus have been discovered yet.
+ * @offline:		Whether the CDMM bus is going offline (or very early
+ *			coming back online), in which case it should be
+ *			reconfigured each time.
+ */
+struct mips_cdmm_bus {
+	phys_addr_t	 phys;
+	void __iomem	*regs;
+	unsigned int	 drbs;
+	unsigned int	 drbs_reserved;
+	bool		 discovered;
+	bool		 offline;
+};
+
+static struct mips_cdmm_bus mips_cdmm_boot_bus;
+static DEFINE_PER_CPU(struct mips_cdmm_bus *, mips_cdmm_buses);
+static atomic_t mips_cdmm_next_id = ATOMIC_INIT(-1);
+
+/**
+ * mips_cdmm_get_bus() - Get the per-CPU CDMM bus information.
+ *
+ * Get information about the per-CPU CDMM bus, if the bus is present.
+ *
+ * The caller must prevent migration to another CPU, either by disabling
+ * pre-emption or by running from a pinned kernel thread.
+ *
+ * Returns:	Pointer to CDMM bus information for the current CPU.
+ *		May return ERR_PTR(-errno) in case of error, so check with
+ *		IS_ERR().
+ */
+static struct mips_cdmm_bus *mips_cdmm_get_bus(void)
+{
+	struct mips_cdmm_bus *bus, **bus_p;
+	unsigned long flags;
+	unsigned int cpu;
+
+	if (!cpu_has_cdmm)
+		return ERR_PTR(-ENODEV);
+
+	cpu = smp_processor_id();
+	/* Avoid early use of per-cpu primitives before initialised */
+	if (cpu == 0)
+		return &mips_cdmm_boot_bus;
+
+	/* Get bus pointer */
+	bus_p = per_cpu_ptr(&mips_cdmm_buses, cpu);
+	local_irq_save(flags);
+	bus = *bus_p;
+	/* Attempt allocation if NULL */
+	if (unlikely(!bus)) {
+		bus = kzalloc(sizeof(*bus), GFP_ATOMIC);
+		if (unlikely(!bus))
+			bus = ERR_PTR(-ENOMEM);
+		else
+			*bus_p = bus;
+	}
+	local_irq_restore(flags);
+	return bus;
+}
+
+/**
+ * mips_cdmm_cur_base() - Find current physical base address of CDMM region.
+ *
+ * Returns:	Physical base address of CDMM region according to cdmmbase CP0
+ *		register, or 0 if the CDMM region is disabled.
+ */
+static phys_addr_t mips_cdmm_cur_base(void)
+{
+	unsigned long cdmmbase = read_c0_cdmmbase();
+
+	if (!(cdmmbase & MIPS_CDMMBASE_EN))
+		return 0;
+
+	return (cdmmbase >> MIPS_CDMMBASE_ADDR_SHIFT)
+		<< MIPS_CDMMBASE_ADDR_START;
+}
+
+/**
+ * mips_cdmm_phys_base() - Choose a physical base address for CDMM region.
+ *
+ * Picking a suitable physical address at which to map the CDMM region is
+ * platform specific, so this weak function can be overridden by platform
+ * code to pick a suitable value if none is configured by the bootloader.
+ * By default this method tries to find a CDMM-specific node in the system
+ * dtb. Note that this won't work for early serial console.
+ */
+phys_addr_t __weak mips_cdmm_phys_base(void)
+{
+	struct device_node *np;
+	struct resource res;
+	int err;
+
+	np = of_find_compatible_node(NULL, NULL, "mti,mips-cdmm");
+	if (np) {
+		err = of_address_to_resource(np, 0, &res);
+		of_node_put(np);
+		if (!err)
+			return res.start;
+	}
+
+	return 0;
+}
+
+/**
+ * mips_cdmm_setup() - Ensure the CDMM bus is initialised and usable.
+ * @bus:	Pointer to bus information for current CPU.
+ *		IS_ERR(bus) is checked, so no need for caller to check.
+ *
+ * The caller must prevent migration to another CPU, either by disabling
+ * pre-emption or by running from a pinned kernel thread.
+ *
+ * Returns	0 on success, -errno on failure.
+ */
+static int mips_cdmm_setup(struct mips_cdmm_bus *bus)
+{
+	unsigned long cdmmbase, flags;
+	int ret = 0;
+
+	if (IS_ERR(bus))
+		return PTR_ERR(bus);
+
+	local_irq_save(flags);
+	/* Don't set up bus a second time unless marked offline */
+	if (bus->offline) {
+		/* If CDMM region is still set up, nothing to do */
+		if (bus->phys == mips_cdmm_cur_base())
+			goto out;
+		/*
+		 * The CDMM region isn't set up as expected, so it needs
+		 * reconfiguring, but then we can stop checking it.
+		 */
+		bus->offline = false;
+	} else if (bus->phys > 1) {
+		goto out;
+	}
+
+	/* If the CDMM region is already configured, inherit that setup */
+	if (!bus->phys)
+		bus->phys = mips_cdmm_cur_base();
+	/* Otherwise, ask platform code for suggestions */
+	if (!bus->phys)
+		bus->phys = mips_cdmm_phys_base();
+	/* Otherwise, copy what other CPUs have done */
+	if (!bus->phys)
+		bus->phys = mips_cdmm_default_base;
+	/* Otherwise, complain once */
+	if (!bus->phys) {
+		bus->phys = 1;
+		/*
+		 * If you hit this, either your bootloader needs to set up the
+		 * CDMM on the boot CPU, or else you need to implement
+		 * mips_cdmm_phys_base() for your platform (see asm/cdmm.h).
+		 */
+		pr_err("cdmm%u: Failed to choose a physical base\n",
+		       smp_processor_id());
+	}
+	/* Already complained? */
+	if (bus->phys == 1) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	/* Record our success for other CPUs to copy */
+	mips_cdmm_default_base = bus->phys;
+
+	pr_debug("cdmm%u: Enabling CDMM region at %pa\n",
+		 smp_processor_id(), &bus->phys);
+
+	/* Enable CDMM */
+	cdmmbase = read_c0_cdmmbase();
+	cdmmbase &= (1ul << MIPS_CDMMBASE_ADDR_SHIFT) - 1;
+	cdmmbase |= (bus->phys >> MIPS_CDMMBASE_ADDR_START)
+			<< MIPS_CDMMBASE_ADDR_SHIFT;
+	cdmmbase |= MIPS_CDMMBASE_EN;
+	write_c0_cdmmbase(cdmmbase);
+	tlbw_use_hazard();
+
+	bus->regs = (void __iomem *)CKSEG1ADDR(bus->phys);
+	bus->drbs = 1 + ((cdmmbase & MIPS_CDMMBASE_SIZE) >>
+			 MIPS_CDMMBASE_SIZE_SHIFT);
+	bus->drbs_reserved = !!(cdmmbase & MIPS_CDMMBASE_CI);
+
+out:
+	local_irq_restore(flags);
+	return ret;
+}
+
+/**
+ * mips_cdmm_early_probe() - Minimally probe for a specific device on CDMM.
+ * @dev_type:	CDMM type code to look for.
+ *
+ * Minimally configure the in-CPU Common Device Memory Map (CDMM) and look for a
+ * specific device. This can be used to find a device very early in boot for
+ * example to configure an early FDC console device.
+ *
+ * The caller must prevent migration to another CPU, either by disabling
+ * pre-emption or by running from a pinned kernel thread.
+ *
+ * Returns:	MMIO pointer to device memory. The caller can read the ACSR
+ *		register to find more information about the device (such as the
+ *		version number or the number of blocks).
+ *		May return IOMEM_ERR_PTR(-errno) in case of error, so check with
+ *		IS_ERR().
+ */
+void __iomem *mips_cdmm_early_probe(unsigned int dev_type)
+{
+	struct mips_cdmm_bus *bus;
+	void __iomem *cdmm;
+	u32 acsr;
+	unsigned int drb, type, size;
+	int err;
+
+	if (WARN_ON(!dev_type))
+		return IOMEM_ERR_PTR(-ENODEV);
+
+	bus = mips_cdmm_get_bus();
+	err = mips_cdmm_setup(bus);
+	if (err)
+		return IOMEM_ERR_PTR(err);
+
+	/* Skip the first block if it's reserved for more registers */
+	drb = bus->drbs_reserved;
+	cdmm = bus->regs;
+
+	/* Look for a specific device type */
+	for (; drb < bus->drbs; drb += size + 1) {
+		acsr = __raw_readl(cdmm + drb * CDMM_DRB_SIZE);
+		type = (acsr & CDMM_ACSR_DEVTYPE) >> CDMM_ACSR_DEVTYPE_SHIFT;
+		if (type == dev_type)
+			return cdmm + drb * CDMM_DRB_SIZE;
+		size = (acsr & CDMM_ACSR_DEVSIZE) >> CDMM_ACSR_DEVSIZE_SHIFT;
+	}
+
+	return IOMEM_ERR_PTR(-ENODEV);
+}
+EXPORT_SYMBOL_GPL(mips_cdmm_early_probe);
+
+/**
+ * mips_cdmm_release() - Release a removed CDMM device.
+ * @dev:	Device object
+ *
+ * Clean up the struct mips_cdmm_device for an unused CDMM device. This is
+ * called automatically by the driver core when a device is removed.
+ */
+static void mips_cdmm_release(struct device *dev)
+{
+	struct mips_cdmm_device *cdev = to_mips_cdmm_device(dev);
+
+	kfree(cdev);
+}
+
+/**
+ * mips_cdmm_bus_discover() - Discover the devices on the CDMM bus.
+ * @bus:	CDMM bus information, must already be set up.
+ */
+static void mips_cdmm_bus_discover(struct mips_cdmm_bus *bus)
+{
+	void __iomem *cdmm;
+	u32 acsr;
+	unsigned int drb, type, size, rev;
+	struct mips_cdmm_device *dev;
+	unsigned int cpu = smp_processor_id();
+	int ret = 0;
+	int id = 0;
+
+	/* Skip the first block if it's reserved for more registers */
+	drb = bus->drbs_reserved;
+	cdmm = bus->regs;
+
+	/* Discover devices */
+	bus->discovered = true;
+	pr_info("cdmm%u discovery (%u blocks)\n", cpu, bus->drbs);
+	for (; drb < bus->drbs; drb += size + 1) {
+		acsr = __raw_readl(cdmm + drb * CDMM_DRB_SIZE);
+		type = (acsr & CDMM_ACSR_DEVTYPE) >> CDMM_ACSR_DEVTYPE_SHIFT;
+		size = (acsr & CDMM_ACSR_DEVSIZE) >> CDMM_ACSR_DEVSIZE_SHIFT;
+		rev  = (acsr & CDMM_ACSR_DEVREV)  >> CDMM_ACSR_DEVREV_SHIFT;
+
+		if (!type)
+			continue;
+
+		pr_info("cdmm%u-%u: @%u (%#x..%#x), type 0x%02x, rev %u\n",
+			cpu, id, drb, drb * CDMM_DRB_SIZE,
+			(drb + size + 1) * CDMM_DRB_SIZE - 1,
+			type, rev);
+
+		dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+		if (!dev)
+			break;
+
+		dev->cpu = cpu;
+		dev->res.start = bus->phys + drb * CDMM_DRB_SIZE;
+		dev->res.end = bus->phys +
+				(drb + size + 1) * CDMM_DRB_SIZE - 1;
+		dev->res.flags = IORESOURCE_MEM;
+		dev->type = type;
+		dev->rev = rev;
+		dev->dev.parent = get_cpu_device(cpu);
+		dev->dev.bus = &mips_cdmm_bustype;
+		dev->dev.id = atomic_inc_return(&mips_cdmm_next_id);
+		dev->dev.release = mips_cdmm_release;
+
+		dev_set_name(&dev->dev, "cdmm%u-%u", cpu, id);
+		++id;
+		ret = device_register(&dev->dev);
+		if (ret)
+			put_device(&dev->dev);
+	}
+}
+
+
+/*
+ * CPU hotplug and initialisation
+ *
+ * All the CDMM driver callbacks need to be executed on the appropriate CPU from
+ * workqueues. For the CPU callbacks, they need to be called for all devices on
+ * that CPU, so the work function calls bus_for_each_dev, using a helper
+ * (generated with BUILD_PERDEV_HELPER) to call the driver callback if the
+ * device's CPU matches.
+ */
+
+/**
+ * BUILD_PERDEV_HELPER() - Helper to call a CDMM driver callback if CPU matches.
+ * @_name:	Name of CDMM driver callback function.
+ *
+ * Generates a bus_for_each_dev callback function to call a specific CDMM driver
+ * callback function for the device if the device's CPU matches that pointed to
+ * by the data argument.
+ *
+ * This is used for informing drivers for all devices on a given CPU of some
+ * event (such as the CPU going online/offline).
+ *
+ * It is expected to already be called from the appropriate CPU.
+ */
+#define BUILD_PERDEV_HELPER(_name)					\
+static int mips_cdmm_##_name##_helper(struct device *dev, void *data)	\
+{									\
+	struct mips_cdmm_device *cdev = to_mips_cdmm_device(dev);	\
+	struct mips_cdmm_driver *cdrv;					\
+	unsigned int cpu = *(unsigned int *)data;			\
+									\
+	if (cdev->cpu != cpu || !dev->driver)				\
+		return 0;						\
+									\
+	cdrv = to_mips_cdmm_driver(dev->driver);			\
+	if (!cdrv->_name)						\
+		return 0;						\
+	return cdrv->_name(cdev);					\
+}
+
+/* bus_for_each_dev callback helper functions */
+BUILD_PERDEV_HELPER(cpu_down)       /* int mips_cdmm_cpu_down_helper(...) */
+BUILD_PERDEV_HELPER(cpu_up)         /* int mips_cdmm_cpu_up_helper(...) */
+
+/**
+ * mips_cdmm_cpu_down_prep() - Callback for CPUHP DOWN_PREP:
+ *			       Tear down the CDMM bus.
+ * @cpu:	unsigned int CPU number.
+ *
+ * This function is executed on the hotplugged CPU and calls the CDMM
+ * driver cpu_down callback for all devices on that CPU.
+ */
+static int mips_cdmm_cpu_down_prep(unsigned int cpu)
+{
+	struct mips_cdmm_bus *bus;
+	long ret;
+
+	/* Inform all the devices on the bus */
+	ret = bus_for_each_dev(&mips_cdmm_bustype, NULL, &cpu,
+			       mips_cdmm_cpu_down_helper);
+
+	/*
+	 * While bus is offline, each use of it should reconfigure it just in
+	 * case it is first use when coming back online again.
+	 */
+	bus = mips_cdmm_get_bus();
+	if (!IS_ERR(bus))
+		bus->offline = true;
+
+	return ret;
+}
+
+/**
+ * mips_cdmm_cpu_online() - Callback for CPUHP ONLINE: Bring up the CDMM bus.
+ * @cpu:	unsigned int CPU number.
+ *
+ * This work_on_cpu callback function is executed on a given CPU to discover
+ * CDMM devices on that CPU, or to call the CDMM driver cpu_up callback for all
+ * devices already discovered on that CPU.
+ *
+ * It is used as work_on_cpu callback function during
+ * initialisation. When CPUs are brought online the function is
+ * invoked directly on the hotplugged CPU.
+ */
+static int mips_cdmm_cpu_online(unsigned int cpu)
+{
+	struct mips_cdmm_bus *bus;
+	long ret;
+
+	bus = mips_cdmm_get_bus();
+	ret = mips_cdmm_setup(bus);
+	if (ret)
+		return ret;
+
+	/* Bus now set up, so we can drop the offline flag if still set */
+	bus->offline = false;
+
+	if (!bus->discovered)
+		mips_cdmm_bus_discover(bus);
+	else
+		/* Inform all the devices on the bus */
+		ret = bus_for_each_dev(&mips_cdmm_bustype, NULL, &cpu,
+				       mips_cdmm_cpu_up_helper);
+
+	return ret;
+}
+
+/**
+ * mips_cdmm_init() - Initialise CDMM bus.
+ *
+ * Initialise CDMM bus, discover CDMM devices for online CPUs, and arrange for
+ * hotplug notifications so the CDMM drivers can be kept up to date.
+ */
+static int __init mips_cdmm_init(void)
+{
+	int ret;
+
+	/* Register the bus */
+	ret = bus_register(&mips_cdmm_bustype);
+	if (ret)
+		return ret;
+
+	/* We want to be notified about new CPUs */
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "bus/cdmm:online",
+				mips_cdmm_cpu_online, mips_cdmm_cpu_down_prep);
+	if (ret < 0)
+		pr_warn("cdmm: Failed to register CPU notifier\n");
+
+	return ret;
+}
+subsys_initcall(mips_cdmm_init);