Message-ID: <20170614112612.GE31492@linux-mips.org>
Date:   Wed, 14 Jun 2017 13:26:12 +0200
From:   Ralf Baechle <ralf@...ux-mips.org>
To:     Matt Redfearn <matt.redfearn@...tec.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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

ping again ...

  Ralf

On Mon, Apr 03, 2017 at 11:11:04AM +0100, Matt Redfearn wrote:

> 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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