clksrc_st_lpc.c

/*
 * Clocksource using the Low Power Timer found in the Low Power Controller (LPC)
 *
 * Copyright (C) 2015 STMicroelectronics – All Rights Reserved
 *
 * Author(s): Francesco Virlinzi <francesco.virlinzi@st.com>
 *	      Ajit Pal Singh <ajitpal.singh@st.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/clk.h>
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/of_address.h>
#include <linux/sched_clock.h>
#include <linux/slab.h>

#include <dt-bindings/mfd/st-lpc.h>

/* Low Power Timer */
#define LPC_LPT_LSB_OFF		0x400
#define LPC_LPT_MSB_OFF		0x404
#define LPC_LPT_START_OFF	0x408

static struct st_clksrc_ddata {
	struct clk		*clk;
	void __iomem		*base;
} ddata;

static void __init st_clksrc_reset(void)
{
	writel_relaxed(0, ddata.base + LPC_LPT_START_OFF);
	writel_relaxed(0, ddata.base + LPC_LPT_MSB_OFF);
	writel_relaxed(0, ddata.base + LPC_LPT_LSB_OFF);
	writel_relaxed(1, ddata.base + LPC_LPT_START_OFF);
}

static u64 notrace st_clksrc_sched_clock_read(void)
{
	return (u64)readl_relaxed(ddata.base + LPC_LPT_LSB_OFF);
}

static int __init st_clksrc_init(void)
{
	unsigned long rate;
	int ret;

	st_clksrc_reset();

	rate = clk_get_rate(ddata.clk);

	sched_clock_register(st_clksrc_sched_clock_read, 32, rate);

	ret = clocksource_mmio_init(ddata.base + LPC_LPT_LSB_OFF,
				    "clksrc-st-lpc", rate, 300, 32,
				    clocksource_mmio_readl_up);
	if (ret) {
		pr_err("clksrc-st-lpc: Failed to register clocksource\n");
		return ret;
	}

	return 0;
}

static int __init st_clksrc_setup_clk(struct device_node *np)
{
	struct clk *clk;

	clk = of_clk_get(np, 0);
	if (IS_ERR(clk)) {
		pr_err("clksrc-st-lpc: Failed to get LPC clock\n");
		return PTR_ERR(clk);
	}

	if (clk_prepare_enable(clk)) {
		pr_err("clksrc-st-lpc: Failed to enable LPC clock\n");
		return -EINVAL;
	}

	if (!clk_get_rate(clk)) {
		pr_err("clksrc-st-lpc: Failed to get LPC clock rate\n");
		clk_disable_unprepare(clk);
		return -EINVAL;
	}

	ddata.clk = clk;

	return 0;
}

static void __init st_clksrc_of_register(struct device_node *np)
{
	int ret;
	uint32_t mode;

	ret = of_property_read_u32(np, "st,lpc-mode", &mode);
	if (ret) {
		pr_err("clksrc-st-lpc: An LPC mode must be provided\n");
		return;
	}

	/* LPC can either run as a Clocksource or in RTC or WDT mode */
	if (mode != ST_LPC_MODE_CLKSRC)
		return;

	ddata.base = of_iomap(np, 0);
	if (!ddata.base) {
		pr_err("clksrc-st-lpc: Unable to map iomem\n");
		return;
	}

	if (st_clksrc_setup_clk(np)) {
		iounmap(ddata.base);
		return;
	}

	if (st_clksrc_init()) {
		clk_disable_unprepare(ddata.clk);
		clk_put(ddata.clk);
		iounmap(ddata.base);
		return;
	}

	pr_info("clksrc-st-lpc: clocksource initialised - running @ %luHz\n",
		clk_get_rate(ddata.clk));
}
CLOCKSOURCE_OF_DECLARE(ddata, "st,stih407-lpc", st_clksrc_of_register);