path: root/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 <linux/ktime.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 bool pcc_channel_acquired;
static ktime_t deadline;
static unsigned int pcc_mpar, pcc_mrtt;

/* pcc mapped address + header size + offset within PCC subspace */
#define GET_PCC_VADDR(offs) (pcc_comm_addr + 0x8 + (offs))

/*
 * Arbitrary Retries in case the remote processor is slow to respond
 * to PCC commands. Keeping it high enough to cover emulators where
 * the processors run painfully slow.
 */
#define NUM_RETRIES 500

static int check_pcc_chan(void)
{
	int ret = -EIO;
	struct acpi_pcct_shared_memory __iomem *generic_comm_base = pcc_comm_addr;
	ktime_t next_deadline = ktime_add(ktime_get(), deadline);

	/* Retry in case the remote processor was too slow to catch up. */
	while (!ktime_after(ktime_get(), next_deadline)) {
		/*
		 * Per spec, prior to boot the PCC space wil be initialized by
		 * platform and should have set the command completion bit when
		 * PCC can be used by OSPM
		 */
		if (readw_relaxed(&generic_comm_base->status) & PCC_CMD_COMPLETE) {
			ret = 0;
			break;
		}
		/*
		 * Reducing the bus traffic in case this loop takes longer than
		 * a few retries.
		 */
		udelay(3);
	}

	return ret;
}

static int send_pcc_cmd(u16 cmd)
{
	int ret = -EIO;
	struct acpi_pcct_shared_memory *generic_comm_base =
		(struct acpi_pcct_shared_memory *) pcc_comm_addr;
	static ktime_t last_cmd_cmpl_time, last_mpar_reset;
	static int mpar_count;
	unsigned int time_delta;

	/*
	 * For CMD_WRITE we know for a fact the caller should have checked
	 * the channel before writing to PCC space
	 */
	if (cmd == CMD_READ) {
		ret = check_pcc_chan();
		if (ret)
			return ret;
	}

	/*
	 * Handle the Minimum Request Turnaround Time(MRTT)
	 * "The minimum amount of time that OSPM must wait after the completion
	 * of a command before issuing the next command, in microseconds"
	 */
	if (pcc_mrtt) {
		time_delta = ktime_us_delta(ktime_get(), last_cmd_cmpl_time);
		if (pcc_mrtt > time_delta)
			udelay(pcc_mrtt - time_delta);
	}

	/*
	 * Handle the non-zero Maximum Periodic Access Rate(MPAR)
	 * "The maximum number of periodic requests that the subspace channel can
	 * support, reported in commands per minute. 0 indicates no limitation."
	 *
	 * This parameter should be ideally zero or large enough so that it can
	 * handle maximum number of requests that all the cores in the system can
	 * collectively generate. If it is not, we will follow the spec and just
	 * not send the request to the platform after hitting the MPAR limit in
	 * any 60s window
	 */
	if (pcc_mpar) {
		if (mpar_count == 0) {
			time_delta = ktime_ms_delta(ktime_get(), last_mpar_reset);
			if (time_delta < 60 * MSEC_PER_SEC) {
				pr_debug("PCC cmd not sent due to MPAR limit");
				return -EIO;
			}
			last_mpar_reset = ktime_get();
			mpar_count = pcc_mpar;
		}
		mpar_count--;
	}

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

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

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

	/*
	 * For READs we need to ensure the cmd completed to ensure
	 * the ensuing read()s can proceed. For WRITEs we dont care
	 * because the actual write()s are done before coming here
	 * and the next READ or WRITE will check if the channel
	 * is busy/free at the entry of this call.
	 *
	 * If Minimum Request Turnaround Time is non-zero, we need
	 * to record the completion time of both READ and WRITE
	 * command for proper handling of MRTT, so we need to check
	 * for pcc_mrtt in addition to CMD_READ
	 */
	if (cmd == CMD_READ || pcc_mrtt) {
		ret = check_pcc_chan();
		if (pcc_mrtt)
			last_cmd_cmpl_time = ktime_get();
	}

	mbox_client_txdone(pcc_channel, ret);
	return ret;
}

static void cppc_chan_tx_done(struct mbox_client *cl, void *msg, int ret)
{
	if (ret < 0)
		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;