linux-next/drivers/acpi/cppc_acpi.c

/*
 * CPPC (Collaborative Processor Performance Control) methods used by CPUfreq drivers.
 *
 * (C) Copyright 2014, 2015 Linaro Ltd.
 * Author: Ashwin Chaugule <ashwin.chaugule@linaro.org>
 *
 * 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; version 2
 * of the License.
 *
 * CPPC describes a few methods for controlling CPU performance using
 * information from a per CPU table called CPC. This table is described in
 * the ACPI v5.0+ specification. The table consists of a list of
 * registers which may be memory mapped or hardware registers and also may
 * include some static integer values.
 *
 * CPU performance is on an abstract continuous scale as against a discretized
 * P-state scale which is tied to CPU frequency only. In brief, the basic
 * operation involves:
 *
 * - OS makes a CPU performance request. (Can provide min and max bounds)
 *
 * - Platform (such as BMC) is free to optimize request within requested bounds
 *   depending on power/thermal budgets etc.
 *
 * - Platform conveys its decision back to OS
 *
 * The communication between OS and platform occurs through another medium
 * called (PCC) Platform Communication Channel. This is a generic mailbox like
 * mechanism which includes doorbell semantics to indicate register updates.
 * See drivers/mailbox/pcc.c for details on PCC.
 *
 * Finer details about the PCC and CPPC spec are available in the ACPI v5.1 and
 * above specifications.
 */

#define pr_fmt(fmt)	"ACPI CPPC: " fmt

#include <linux/cpufreq.h>
#include <linux/delay.h>

#include <acpi/cppc_acpi.h>
/*
 * Lock to provide mutually exclusive access to the PCC
 * channel. e.g. When the remote updates the shared region
 * with new data, the reader needs to be protected from
 * other CPUs activity on the same channel.
 */
static DEFINE_SPINLOCK(pcc_lock);

/*
 * The cpc_desc structure contains the ACPI register details
 * as described in the per CPU _CPC tables. The details
 * include the type of register (e.g. PCC, System IO, FFH etc.)
 * and destination addresses which lets us READ/WRITE CPU performance
 * information using the appropriate I/O methods.
 */
static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);

/* This layer handles all the PCC specifics for CPPC. */
static struct mbox_chan *pcc_channel;
static void __iomem *pcc_comm_addr;
static u64 comm_base_addr;
static int pcc_subspace_idx = -1;
static u16 pcc_cmd_delay;
static bool pcc_channel_acquired;

/*
 * Arbitrary Retries in case the remote processor is slow to respond
 * to PCC commands.
 */
#define NUM_RETRIES 500

static int send_pcc_cmd(u16 cmd)
{
	int retries, result = -EIO;
	struct acpi_pcct_hw_reduced *pcct_ss = pcc_channel->con_priv;
	struct acpi_pcct_shared_memory *generic_comm_base =
		(struct acpi_pcct_shared_memory *) pcc_comm_addr;
	u32 cmd_latency = pcct_ss->latency;

	/* Min time OS should wait before sending next command. */
	udelay(pcc_cmd_delay);

	/* Write to the shared comm region. */
	writew(cmd, &generic_comm_base->command);

	/* Flip CMD COMPLETE bit */
	writew(0, &generic_comm_base->status);

	/* Ring doorbell */
	result = mbox_send_message(pcc_channel, &cmd);
	if (result < 0) {
		pr_err("Err sending PCC mbox message. cmd:%d, ret:%d\n",
				cmd, result);
		return result;
	}

	/* Wait for a nominal time to let platform process command. */
	udelay(cmd_latency);

	/* Retry in case the remote processor was too slow to catch up. */
	for (retries = NUM_RETRIES; retries > 0; retries--) {
		if (readw_relaxed(&generic_comm_base->status) & PCC_CMD_COMPLETE) {
			result = 0;
			break;
		}
	}

	mbox_client_txdone(pcc_channel, result);
	return result;
}

static void cppc_chan_tx_done(struct mbox_client *cl, void *msg, int ret)
{
	if (ret)
		pr_debug("TX did not complete: CMD sent:%x, ret:%d\n",
				*(u16 *)msg, ret);
	else
		pr_debug("TX completed. CMD sent:%x, ret:%d\n",
				*(u16 *)msg, ret);
}

struct mbox_client cppc_mbox_cl = {
	.tx_done = cppc_chan_tx_done,
	.knows_txdone = true,
};

static int acpi_get_psd(struct cpc_desc *cpc_ptr, acpi_handle handle)
{
	int result = -EFAULT;
	acpi_status status = AE_OK;
	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
	struct acpi_buffer format = {sizeof("NNNNN"), "NNNNN"};
	struct acpi_buffer state = {0, NULL};
	union acpi_object  *psd = NULL;
	struct acpi_psd_package *pdomain;

	status = acpi_evaluate_object_typed(handle, "_PSD", NULL, &buffer,
			ACPI_TYPE_PACKAGE);
	if (ACPI_FAILURE(status))
		return -ENODEV;

	psd = buffer.pointer;
	if (!psd || psd->package.count != 1) {
		pr_debug("Invalid _PSD data\n");
		goto end;
	}

	pdomain = &(cpc_ptr->domain_info);

	state.length = sizeof(struct acpi_psd_package);
	state.pointer = pdomain;

	status = acpi_extract_package(&(psd->package.elements[0]),
		&format, &state);
	if (ACPI_FAILURE(status)) {
		pr_debug("Invalid _PSD data for CPU:%d\n", cpc_ptr->cpu_id);
		goto end;
	}

	if (pdomain->num_entries != ACPI_PSD_REV0_ENTRIES) {
		pr_debug("Unknown _PSD:num_entries for CPU:%d\n", cpc_ptr->cpu_id);
		goto end;
	}

	if (pdomain->revision != ACPI_PSD_REV0_REVISION) {
		pr_debug("Unknown _PSD:revision for CPU: %d\n", cpc_ptr->cpu_id);
		goto end;
	}

	if (pdomain->coord_type != DOMAIN_COORD_TYPE_SW_ALL &&
	    pdomain->coord_type != DOMAIN_COORD_TYPE_SW_ANY &&
	    pdomain->coord_type != DOMAIN_COORD_TYPE_HW_ALL) {
		pr_debug("Invalid _PSD:coord_type for CPU:%d\n", cpc_ptr->cpu_id);
		goto end;
	}

	result = 0;
end:
	kfree(buffer.pointer);
	return result;
}

/**
 * acpi_get_psd_map - Map the CPUs in a common freq domain.
 * @all_cpu_data: Ptrs to CPU specific CPPC data including PSD info.
 *
 *	Return: 0 for success or negative value for err.
 */
int acpi_get_psd_map(struct cpudata **all_cpu_data)
{
	int count_target;
	int retval = 0;
	unsigned int i, j;
	cpumask_var_t covered_cpus;
	struct cpudata *pr, *match_pr;
	struct acpi_psd_package *pdomain;
	struct acpi_psd_package *match_pdomain;
	struct cpc_desc *cpc_ptr, *match_cpc_ptr;

	if (!zalloc_cpumask_var(&covered_cpus, GFP_KERNEL))
		return -ENOMEM;

	/*
	 * Now that we have _PSD data from all CPUs, lets setup P-state
	 * domain info.
	 */
	for_each_possible_cpu(i) {
		pr = all_cpu_data[i];
		if (!pr)
			continue;

		if (cpumask_test_cpu(i, covered_cpus))
			continue;

		cpc_ptr = per_cpu(cpc_desc_ptr, i);
		if (!cpc_ptr)
			continue;

		pdomain = &(cpc_ptr->domain_info);
		cpumask_set_cpu(i, pr->shared_cpu_map);
		cpumask_set_cpu(i, covered_cpus);
		if (pdomain->num_processors <= 1)
			continue;

		/* Validate the Domain info */
		count_target = pdomain->num_processors;
		if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ALL)
			pr->shared_type = CPUFREQ_SHARED_TYPE_ALL;
		else if (pdomain->coord_type == DOMAIN_COORD_TYPE_HW_ALL)
			pr->shared_type = CPUFREQ_SHARED_TYPE_HW;
		else if (pdomain->coord_type == DOMAIN_COORD_TYPE_SW_ANY)
			pr->shared_type = CPUFREQ_SHARED_TYPE_ANY;

		for_each_possible_cpu(j) {
			if (i == j)
				continue;

			match_cpc_ptr = per_cpu(cpc_desc_ptr, j);
			if (!match_cpc_ptr)
				continue;

			match_pdomain = &(match_cpc_ptr->domain_info);
			if (match_pdomain->domain != pdomain->domain)
				continue;

			/* Here i and j are in the same domain */
			if (match_pdomain->num_processors != count_target) {
				retval = -EFAULT;
				goto err_ret;
			}

			if (pdomain->coord_type != match_pdomain->coord_type) {
				retval = -EFAULT;
				goto err_ret;
			}

			cpumask_set_cpu(j, covered_cpus);
			cpumask_set_cpu(j, pr->shared_cpu_map);
		}

		for_each_possible_cpu(j) {
			if (i == j)
				continue;

			match_pr = all_cpu_data[j];
			if (!match_pr)
				continue;

			match_cpc_ptr = per_cpu(cpc_desc_ptr, j);
			if (!match_cpc_ptr)
				continue;

			match_pdomain = &(match_cpc_ptr->domain_info);
			if (match_pdomain->domain != pdomain->domain)
				continue;

			match_pr->shared_type = pr->shared_type;
			cpumask_copy(match_pr->shared_cpu_map,
				     pr->shared_cpu_map);
		}
	}

err_ret:
	for_each_possible_cpu(i) {
		pr = all_cpu_data[i];
		if (!pr)
			continue;

		/* Assume no coordination on any error parsing domain info */
		if (retval) {
			cpumask_clear(pr->shared_cpu_map);
			cpumask_set_cpu(i, pr->shared_cpu_map);
			pr->shared_type = CPUFREQ_SHARED_TYPE_ALL;
		}
	}

	free_cpumask_var(covered_cpus);
	return retval;
}
EXPORT_SYMBOL_GPL(acpi_get_psd_map);

static int register_pcc_channel(int pcc_subspace_idx)
{
	struct acpi_pcct_hw_reduced *cppc_ss;
	unsigned int len;

	if (pcc_subspace_idx >= 0) {
		pcc_channel = pcc_mbox_request_channel(&cppc_mbox_cl,
				pcc_subspace_idx);

		if (IS_ERR(pcc_channel)) {
			pr_err("Failed to find PCC communication channel\n");
			return -ENODEV;
		}

		/*
		 * The PCC mailbox controller driver should
		 * have parsed the PCCT (global table of all
		 * PCC channels) and stored pointers to the
		 * subspace communication region in con_priv.
		 */
		cppc_ss = pcc_channel->con_priv;

		if (!cppc_ss) {
			pr_err("No PCC subspace found for CPPC\n");
			return -ENODEV;
		}

		/*
		 * This is the shared communication region
		 * for the OS and Platform to communicate over.
		 */
		comm_base_addr = cppc_ss->base_address;
		len = cppc_ss->length;
		pcc_cmd_delay = cppc_ss->min_turnaround_time;

		pcc_comm_addr = acpi_os_ioremap(comm_base_addr, len);
		if (!pcc_comm_addr) {
			pr_err("Failed to ioremap PCC comm region mem\n");
			return -ENOMEM;
		}

		/* Set flag so that we dont come here for each CPU. */
		pcc_channel_acquired = true;
	}

	return 0;
}

/*
 * An example CPC table looks like the following.
 *
 *	Name(_CPC, Package()
 *			{
 *			17,
 *			NumEntries
 *			1,
 *			// Revision
 *			ResourceTemplate(){Register(PCC, 32, 0, 0x120, 2)},
 *			// Highest Performance
 *			ResourceTemplate(){Register(PCC, 32, 0, 0x124, 2)},
 *			// Nominal Performance
 *			ResourceTemplate(){Register(PCC, 32, 0, 0x128, 2)},
 *			// Lowest Nonlinear Performance
 *			ResourceTemplate(){Register(PCC, 32, 0, 0x12C, 2)},
 *			// Lowest Performance
 *			ResourceTemplate(){Register(PCC, 32, 0, 0x130, 2)},
 *			// Guaranteed Performance Register
 *			ResourceTemplate(){Register(PCC, 32, 0, 0x110, 2)},
 *			// Desired Performance Register
 *			ResourceTemplate(){Register(SystemMemory, 0, 0, 0, 0)},
 *			..
 *			..
 *			..
 *
 *		}
 * Each Register() encodes how to access that specific register.
 * e.g. a sample PCC entry has the following encoding:
 *
 *	Register (
 *		PCC,
 *		AddressSpaceKeyword
 *		8,
 *		//RegisterBitWidth
 *		8,
 *		//RegisterBitOffset
 *		0x30,
 *		//RegisterAddress
 *		9
 *		//AccessSize (subspace ID)
 *		0
 *		)
 *	}
 */

/**
 * acpi_cppc_processor_probe - Search for per CPU _CPC objects.
 * @pr: Ptr to acpi_processor containing this CPUs logical Id.
 *
 *	Return: 0 for success or negative value for err.
 */
int acpi_cppc_processor_probe(struct acpi_processor *pr)
{
	struct acpi_buffer output = {ACPI_ALLOCATE_BUFFER, NULL};
	union acpi_object *out_obj, *cpc_obj;
	struct cpc_desc *cpc_ptr;
	struct cpc_reg *gas_t;
	acpi_handle handle = pr->handle;
	unsigned int num_ent, i, cpc_rev;
	acpi_status status;
	int ret = -EFAULT;

	/* Parse the ACPI _CPC table for this cpu. */
	status = acpi_evaluate_object_typed(handle, "_CPC", NULL, &output,
			ACPI_TYPE_PACKAGE);
	if (ACPI_FAILURE(status)) {
		ret = -ENODEV;
		goto out_buf_free;
	}

	out_obj = (union acpi_object *) output.pointer;

	cpc_ptr = kzalloc(sizeof(struct cpc_desc), GFP_KERNEL);
	if (!cpc_ptr) {
		ret = -ENOMEM;
		goto out_buf_free;
	}

	/* First entry is NumEntries. */
	cpc_obj = &out_obj->package.elements[0];
	if (cpc_obj->type == ACPI_TYPE_INTEGER)	{
		num_ent = cpc_obj->integer.value;
	} else {
		pr_debug("Unexpected entry type(%d) for NumEntries\n",
				cpc_obj->type);
		goto out_free;
	}

	/* Only support CPPCv2. Bail otherwise. */
	if (num_ent != CPPC_NUM_ENT) {
		pr_debug("Firmware exports %d entries. Expected: %d\n",
				num_ent, CPPC_NUM_ENT);
		goto out_free;
	}

	/* Second entry should be revision. */
	cpc_obj = &out_obj->package.elements[1];
	if (cpc_obj->type == ACPI_TYPE_INTEGER)	{
		cpc_rev = cpc_obj->integer.value;
	} else {
		pr_debug("Unexpected entry type(%d) for Revision\n",
				cpc_obj->type);
		goto out_free;
	}

	if (cpc_rev != CPPC_REV) {
		pr_debug("Firmware exports revision:%d. Expected:%d\n",
				cpc_rev, CPPC_REV);
		goto out_free;
	}

	/* Iterate through remaining entries in _CPC */
	for (i = 2; i < num_ent; i++) {
		cpc_obj = &out_obj->package.elements[i];

		if (cpc_obj->type == ACPI_TYPE_INTEGER)	{
			cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_INTEGER;
			cpc_ptr->cpc_regs[i-2].cpc_entry.int_value = cpc_obj->integer.value;
		} else if (cpc_obj->type == ACPI_TYPE_BUFFER) {
			gas_t = (struct cpc_reg *)
				cpc_obj->buffer.pointer;

			/*
			 * The PCC Subspace index is encoded inside
			 * the CPC table entries. The same PCC index
			 * will be used for all the PCC entries,
			 * so extract it only once.
			 */
			if (gas_t->space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
				if (pcc_subspace_idx < 0)
					pcc_subspace_idx = gas_t->access_width;
				else if (pcc_subspace_idx != gas_t->access_width) {
					pr_debug("Mismatched PCC ids.\n");
					goto out_free;
				}
			} else if (gas_t->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY) {
				/* Support only PCC and SYS MEM type regs */
				pr_debug("Unsupported register type: %d\n", gas_t->space_id);
				goto out_free;
			}

			cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_BUFFER;
			memcpy(&cpc_ptr->cpc_regs[i-2].cpc_entry.reg, gas_t, sizeof(*gas_t));
		} else {
			pr_debug("Err in entry:%d in CPC table of CPU:%d \n", i, pr->id);
			goto out_free;
		}
	}
	/* Store CPU Logical ID */
	cpc_ptr->cpu_id = pr->id;

	/* Plug it into this CPUs CPC descriptor. */
	per_cpu(cpc_desc_ptr, pr->id) = cpc_ptr;

	/* Parse PSD data for this CPU */
	ret = acpi_get_psd(cpc_ptr, handle);
	if (ret)
		goto out_free;

	/* Register PCC channel once for all CPUs. */
	if (!pcc_channel_acquired) {
		ret = register_pcc_channel(pcc_subspace_idx);
		if (ret)
			goto out_free;
	}

	/* Everything looks okay */
	pr_debug("Parsed CPC struct for CPU: %d\n", pr->id);

	kfree(output.pointer);
	return 0;

out_free:
	kfree(cpc_ptr);

out_buf_free:
	kfree(output.pointer);
	return ret;
}
EXPORT_SYMBOL_GPL(acpi_cppc_processor_probe);

/**
 * acpi_cppc_processor_exit - Cleanup CPC structs.
 * @pr: Ptr to acpi_processor containing this CPUs logical Id.
 *
 * Return: Void
 */
void acpi_cppc_processor_exit(struct acpi_processor *pr)
{
	struct cpc_desc *cpc_ptr;
	cpc_ptr = per_cpu(cpc_desc_ptr, pr->id);
	kfree(cpc_ptr);
}
EXPORT_SYMBOL_GPL(acpi_cppc_processor_exit);

static u64 get_phys_addr(struct cpc_reg *reg)
{
	/* PCC communication addr space begins at byte offset 0x8. */
	if (reg->space_id == ACPI_ADR_SPACE_PLATFORM_COMM)
		return (u64)comm_base_addr + 0x8 + reg->address;
	else
		return reg->address;
}

static void cpc_read(struct cpc_reg *reg, u64 *val)
{
	u64 addr = get_phys_addr(reg);

	acpi_os_read_memory((acpi_physical_address)addr,
			val, reg->bit_width);
}

static void cpc_write(struct cpc_reg *reg, u64 val)
{
	u64 addr = get_phys_addr(reg);

	acpi_os_write_memory((acpi_physical_address)addr,
			val, reg->bit_width);
}

/**
 * cppc_get_perf_caps - Get a CPUs performance capabilities.
 * @cpunum: CPU from which to get capabilities info.
 * @perf_caps: ptr to cppc_perf_caps. See cppc_acpi.h
 *
 * Return: 0 for success with perf_caps populated else -ERRNO.
 */
int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
{
	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
	struct cpc_register_resource *highest_reg, *lowest_reg, *ref_perf,
								 *nom_perf;
	u64 high, low, ref, nom;
	int ret = 0;

	if (!cpc_desc) {
		pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
		return -ENODEV;
	}

	highest_reg = &cpc_desc->cpc_regs[HIGHEST_PERF];
	lowest_reg = &cpc_desc->cpc_regs[LOWEST_PERF];
	ref_perf = &cpc_desc->cpc_regs[REFERENCE_PERF];
	nom_perf = &cpc_desc->cpc_regs[NOMINAL_PERF];

	spin_lock(&pcc_lock);

	/* Are any of the regs PCC ?*/
	if ((highest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
			(lowest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
			(ref_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
			(nom_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
		/* Ring doorbell once to update PCC subspace */
		if (send_pcc_cmd(CMD_READ)) {
			ret = -EIO;
			goto out_err;
		}
	}

	cpc_read(&highest_reg->cpc_entry.reg, &high);
	perf_caps->highest_perf = high;

	cpc_read(&lowest_reg->cpc_entry.reg, &low);
	perf_caps->lowest_perf = low;

	cpc_read(&ref_perf->cpc_entry.reg, &ref);
	perf_caps->reference_perf = ref;

	cpc_read(&nom_perf->cpc_entry.reg, &nom);
	perf_caps->nominal_perf = nom;

	if (!ref)
		perf_caps->reference_perf = perf_caps->nominal_perf;

	if (!high || !low || !nom)
		ret = -EFAULT;

out_err:
	spin_unlock(&pcc_lock);
	return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_perf_caps);

/**
 * cppc_get_perf_ctrs - Read a CPUs performance feedback counters.
 * @cpunum: CPU from which to read counters.
 * @perf_fb_ctrs: ptr to cppc_perf_fb_ctrs. See cppc_acpi.h
 *
 * Return: 0 for success with perf_fb_ctrs populated else -ERRNO.
 */
int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
{
	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
	struct cpc_register_resource *delivered_reg, *reference_reg;
	u64 delivered, reference;
	int ret = 0;

	if (!cpc_desc) {
		pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
		return -ENODEV;
	}

	delivered_reg = &cpc_desc->cpc_regs[DELIVERED_CTR];
	reference_reg = &cpc_desc->cpc_regs[REFERENCE_CTR];

	spin_lock(&pcc_lock);

	/* Are any of the regs PCC ?*/
	if ((delivered_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
			(reference_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
		/* Ring doorbell once to update PCC subspace */
		if (send_pcc_cmd(CMD_READ)) {
			ret = -EIO;
			goto out_err;
		}
	}

	cpc_read(&delivered_reg->cpc_entry.reg, &delivered);
	cpc_read(&reference_reg->cpc_entry.reg, &reference);

	if (!delivered || !reference) {
		ret = -EFAULT;
		goto out_err;
	}

	perf_fb_ctrs->delivered = delivered;
	perf_fb_ctrs->reference = reference;

	perf_fb_ctrs->delivered -= perf_fb_ctrs->prev_delivered;
	perf_fb_ctrs->reference -= perf_fb_ctrs->prev_reference;

	perf_fb_ctrs->prev_delivered = delivered;
	perf_fb_ctrs->prev_reference = reference;

out_err:
	spin_unlock(&pcc_lock);
	return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);

/**
 * cppc_set_perf - Set a CPUs performance controls.
 * @cpu: CPU for which to set performance controls.
 * @perf_ctrls: ptr to cppc_perf_ctrls. See cppc_acpi.h
 *
 * Return: 0 for success, -ERRNO otherwise.
 */
int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
{
	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
	struct cpc_register_resource *desired_reg;
	int ret = 0;

	if (!cpc_desc) {
		pr_debug("No CPC descriptor for CPU:%d\n", cpu);
		return -ENODEV;
	}

	desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];

	spin_lock(&pcc_lock);

	/*
	 * Skip writing MIN/MAX until Linux knows how to come up with
	 * useful values.
	 */
	cpc_write(&desired_reg->cpc_entry.reg, perf_ctrls->desired_perf);

	/* Is this a PCC reg ?*/
	if (desired_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
		/* Ring doorbell so Remote can get our perf request. */
		if (send_pcc_cmd(CMD_WRITE))
			ret = -EIO;
	}

	spin_unlock(&pcc_lock);

	return ret;
}
EXPORT_SYMBOL_GPL(cppc_set_perf);