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/iopoll.h>
#include <linux/ktime.h>
#include <linux/rwsem.h>
#include <linux/wait.h>

#include <acpi/cppc_acpi.h>

struct cppc_pcc_data {
	struct mbox_chan *pcc_channel;
	void __iomem *pcc_comm_addr;
	bool pcc_channel_acquired;
	unsigned int deadline_us;
	unsigned int pcc_mpar, pcc_mrtt, pcc_nominal;

	bool pending_pcc_write_cmd;	/* Any pending/batched PCC write cmds? */
	bool platform_owns_pcc;		/* Ownership of PCC subspace */
	unsigned int pcc_write_cnt;	/* Running count of PCC write commands */

	/*
	 * Lock to provide controlled access to the PCC channel.
	 *
	 * For performance critical usecases(currently cppc_set_perf)
	 *	We need to take read_lock and check if channel belongs to OSPM
	 * before reading or writing to PCC subspace
	 *	We need to take write_lock before transferring the channel
	 * ownership to the platform via a Doorbell
	 *	This allows us to batch a number of CPPC requests if they happen
	 * to originate in about the same time
	 *
	 * For non-performance critical usecases(init)
	 *	Take write_lock for all purposes which gives exclusive access
	 */
	struct rw_semaphore pcc_lock;

	/* Wait queue for CPUs whose requests were batched */
	wait_queue_head_t pcc_write_wait_q;
	ktime_t last_cmd_cmpl_time;
	ktime_t last_mpar_reset;
	int mpar_count;
	int refcount;
};

/* Array to represent the PCC channel per subspace ID */
static struct cppc_pcc_data *pcc_data[MAX_PCC_SUBSPACES];
/* The cpu_pcc_subspace_idx contains per CPU subspace ID */
static DEFINE_PER_CPU(