// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2019 Daniel Palmer <daniel@thingy.jp>
 */

#include <linux/clk-provider.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/of_address.h>
#include <linux/platform_device.h>

/*
 * This IP is not documented outside of the messy vendor driver.
 * Below is what we think the registers look like based on looking at
 * the vendor code and poking at the hardware:
 *
 * 0x140 -- LPF low. Seems to store one half of the clock transition
 * 0x144 /
 * 0x148 -- LPF high. Seems to store one half of the clock transition
 * 0x14c /
 * 0x150 -- vendor code says "toggle lpf enable"
 * 0x154 -- mu?
 * 0x15c -- lpf_update_count?
 * 0x160 -- vendor code says "switch to LPF". Clock source config? Register bank?
 * 0x164 -- vendor code says "from low to high" which seems to mean transition from LPF low to
 * LPF high.
 * 0x174 -- Seems to be the PLL lock status bit
 * 0x180 -- Seems to be the current frequency, this might need to be populated by software?
 * 0x184 /  The vendor driver uses these to set the initial value of LPF low
 *
 * Frequency seems to be calculated like this:
 * (parent clock (432mhz) / register_magic_value) * 16 * 524288
 * Only the lower 24 bits of the resulting value will be used. In addition, the
 * PLL doesn't seem to be able to lock on frequencies lower than 220 MHz, as
 * divisor 0xfb586f (220 MHz) works but 0xfb7fff locks up.
 *
 * Vendor values:
 * frequency - register value
 *
 * 400000000  - 0x0067AE14
 * 600000000  - 0x00451EB8,
 * 800000000  - 0x0033D70A,
 * 1000000000 - 0x002978d4,
 */

#define REG_LPF_LOW_L		0x140
#define REG_LPF_LOW_H		0x144
#define REG_LPF_HIGH_BOTTOM	0x148
#define REG_LPF_HIGH_TOP	0x14c
#define REG_LPF_TOGGLE		0x150
#define REG_LPF_MYSTERYTWO	0x154
#define REG_LPF_UPDATE_COUNT	0x15c
#define REG_LPF_MYSTERYONE	0x160
#define REG_LPF_TRANSITIONCTRL	0x164
#define REG_LPF_LOCK		0x174
#define REG_CURRENT		0x180

#define LPF_LOCK_TIMEOUT	100000000

#define MULTIPLIER_1		16
#define MULTIPLIER_2		524288
#define MULTIPLIER		(MULTIPLIER_1 * MULTIPLIER_2)

struct msc313_cpupll {
	void __iomem *base;
	struct clk_hw clk_hw;
};

#define to_cpupll(_hw) container_of(_hw, struct msc313_cpupll, clk_hw)

static u32 msc313_cpupll_reg_read32(struct msc313_cpupll *cpupll, unsigned int reg)
{
	u32 value;

	value = ioread16(cpupll->base + reg + 4) << 16;
	value |= ioread16(cpupll->base + reg);

	return value;
}

static void msc313_cpupll_reg_write32(struct msc313_cpupll *cpupll, unsigned int reg, u32 value)
{
	u16 l = value & 0xffff, h = (value >> 16) & 0xffff;

	iowrite16(l, cpupll->base + reg);
	iowrite16(h, cpupll->base + reg + 4);
}

static void msc313_cpupll_setfreq(struct msc313_cpupll *cpupll, u32 regvalue)
{
	ktime_t timeout;

	msc313_cpupll_reg_write32(cpupll, REG_LPF_HIGH_BOTTOM, regvalue);

	iowrite16(0x1, cpupll->base + REG_LPF_MYSTERYONE);
	iowrite16(0x6, cpupll->base + REG_LPF_MYSTERYTWO);
	iowrite16(0x8, cpupll->base + REG_LPF_UPDATE_COUNT);
	iowrite16(BIT(12), cpupll->base + REG_LPF_TRANSITIONCTRL);

	iowrite16(0, cpupll->base + REG_LPF_TOGGLE);
	iowrite16(1, cpupll->base + REG_LPF_TOGGLE);

	timeout = ktime_add_ns(ktime_get(), LPF_LOCK_TIMEOUT);
	while (!(ioread16(cpupll->base + REG_LPF_LOCK))) {
		if (ktime_after(ktime_get(), timeout)) {
			pr_err("timeout waiting for LPF_LOCK\n");
			return;
		}
		cpu_relax();
	}

	iowrite16(0, cpupll->base + REG_LPF_TOGGLE);

	msc313_cpupll_reg_write32(cpupll, REG_LPF_LOW_L, regvalue);
}

static unsigned long msc313_cpupll_frequencyforreg(u32 reg, unsigned long parent_rate)
{
	unsigned long long prescaled = ((unsigned long long)parent_rate) * MULTIPLIER;

	if (prescaled == 0 || reg == 0)
		return 0;
	return DIV_ROUND_DOWN_ULL(prescaled, reg);
}

static u32 msc313_cpupll_regforfrequecy(unsigned long rate, unsigned long parent_rate)
{
	unsigned long long prescaled = ((unsigned long long)parent_rate) * MULTIPLIER;

	if (prescaled == 0 || rate == 0)
		return 0;
	return DIV_ROUND_UP_ULL(prescaled, rate);
}

static unsigned long msc313_cpupll_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
{
	struct msc313_cpupll *cpupll = to_cpupll(hw);

	return msc313_cpupll_frequencyforreg(msc313_cpupll_reg_read32(cpupll, REG_LPF_LOW_L),
					     parent_rate);
}

static long msc313_cpupll_round_rate(struct clk_hw *hw, unsigned long rate,
				     unsigned long *parent_rate)
{
	u32 reg = msc313_cpupll_regforfrequecy(rate, *parent_rate);
	long rounded = msc313_cpupll_frequencyforreg(reg, *parent_rate);

	/*
	 * This is my poor attempt at making sure the resulting
	 * rate doesn't overshoot the requested rate.
	 */
	for (; rounded >= rate && reg > 0; reg--)
		rounded = msc313_cpupll_frequencyforreg(reg, *parent_rate);

	return rounded;
}

static int msc313_cpupll_set_rate(struct clk_hw *hw, unsigned long rate, unsigned long parent_rate)
{
	struct msc313_cpupll *cpupll = to_cpupll(hw);
	u32 reg = msc313_cpupll_regforfrequecy(rate, parent_rate);

	msc313_cpupll_setfreq(cpupll, reg);

	return 0;
}

static const struct clk_ops msc313_cpupll_ops = {
	.recalc_rate	= msc313_cpupll_recalc_rate,
	.round_rate	= msc313_cpupll_round_rate,
	.set_rate	= msc313_cpupll_set_rate,
};

static const struct of_device_id msc313_cpupll_of_match[] = {
	{ .compatible = "mstar,msc313-cpupll" },
	{}
};

static int msc313_cpupll_probe(struct platform_device *pdev)
{
	struct clk_init_data clk_init = {};
	struct clk_parent_data cpupll_parent = { .index	= 0 };
	struct device *dev = &pdev->dev;
	struct msc313_cpupll *cpupll;
	int ret;

	cpupll = devm_kzalloc(&pdev->dev, sizeof(*cpupll), GFP_KERNEL);
	if (!cpupll)
		return -ENOMEM;

	cpupll->base = devm_platform_ioremap_resource(pdev, 0);
	if (IS_ERR(cpupll->base))
		return PTR_ERR(cpupll->base);

	/* LPF might not contain the current frequency so fix that up */
	msc313_cpupll_reg_write32(cpupll, REG_LPF_LOW_L,
				  msc313_cpupll_reg_read32(cpupll, REG_CURRENT));

	clk_init.name = dev_name(dev);
	clk_init.ops = &msc313_cpupll_ops;
	clk_init.parent_data = &cpupll_parent;
	clk_init.num_parents = 1;
	cpupll->clk_hw.init = &clk_init;

	ret = devm_clk_hw_register(dev, &cpupll->clk_hw);
	if (ret)
		return ret;

	return devm_of_clk_add_hw_provider(&pdev->dev, of_clk_hw_simple_get, &cpupll->clk_hw);
}

static struct platform_driver msc313_cpupll_driver = {
	.driver = {
		.name = "mstar-msc313-cpupll",
		.of_match_table = msc313_cpupll_of_match,
	},
	.probe = msc313_cpupll_probe,
};
builtin_platform_driver(msc313_cpupll_driver);