Message-ID: <95ec7c9a-f954-1a66-20c3-99e1fa4b49f7@imgtec.com>
Date:   Mon, 3 Apr 2017 11:11:04 +0100
From:   Matt Redfearn <matt.redfearn@...tec.com>
To:     Ralf Baechle <ralf@...ux-mips.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     <linux-mips@...ux-mips.org>, <linux-remoteproc@...r.kernel.org>,
        <lisa.parratt@...tec.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 3/4] remoteproc/MIPS: Add a remoteproc driver for MIPS

Hi Bjorn,

Please could you provide any comments / review on this driver?

Thanks,

Matt


On 23/03/17 16:37, Matt Redfearn wrote:
> This driver allows a MIPS processor offlined from Linux to be used as a
> remote processor. The processor can then handle real-time tasks or
> perform coprocessing while remaining processors are available to Linux,
> effectively making the system hybrid of SMP Linux and AMP.
>
> A sysfs interface is provided to allow control of which system CPUs may
> be acquired by the driver when offlined from 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.
>
> Example firmware and host executables to test them are located at [1].
>
> [1] https://github.com/MIPS/mips-rproc-example
>
> Signed-off-by: Lisa Parratt <lisa.parratt@...tec.com>
> Signed-off-by: Matt Redfearn <matt.redfearn@...tec.com>
>
> ---
>
> Changes in v6:
> Change to set_current_state() as set_task_state has been removed.
>
> 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               | 599 +++++++++++++++++++++
>   4 files changed, 624 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@...tec.com>
> +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 65f86bc24c07..558b67184723 100644
> --- a/drivers/remoteproc/Kconfig
> +++ b/drivers/remoteproc/Kconfig
> @@ -71,6 +71,17 @@ 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 ffc5e430df27..9525debba686 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_RPROC_COMMON)		+= qcom_common.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..9a0e5e06c0b1
> --- /dev/null
> +++ b/drivers/remoteproc/mips_remoteproc.c
> @@ -0,0 +1,599 @@
> +/*
> + * MIPS Remote Processor driver
> + *
> + * Copyright (C) 2016 Imagination Technologies
> + * Lisa Parratt <lisa.parratt@...tec.com>
> + * Matt Redfearn <matt.redfearn@...tec.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.
> + */
> +
> +#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 <linux/sched/task.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);
> +
> +	/* We're done with the task struct that provided the stack we've used */
> +	set_current_state(TASK_DEAD);
> +
> +	/* 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));
> +
> +	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");

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