drivers/clk/clk-apple-nco.c

// SPDX-License-Identifier: GPL-2.0-only OR MIT
/*
 * Driver for an SoC block (Numerically Controlled Oscillator)
 * found on t8103 (M1) and other Apple chips
 *
 * Copyright (C) The Asahi Linux Contributors
 */

#include <linux/bits.h>
#include <linux/bitfield.h>
#include <linux/clk-provider.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/math64.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/spinlock.h>

#define NCO_CHANNEL_STRIDE	0x4000
#define NCO_CHANNEL_REGSIZE	20

#define REG_CTRL	0
#define CTRL_ENABLE	BIT(31)
#define REG_DIV		4
#define DIV_FINE	GENMASK(1, 0)
#define DIV_COARSE	GENMASK(12, 2)
#define REG_INC1	8
#define REG_INC2	12
#define REG_ACCINIT	16

/*
 * Theory of operation (postulated)
 *
 * The REG_DIV register indirectly expresses a base integer divisor, roughly
 * corresponding to twice the desired ratio of input to output clock. This
 * base divisor is adjusted on a cycle-by-cycle basis based on the state of a
 * 32-bit phase accumulator to achieve a desired precise clock ratio over the
 * long term.
 *
 * Specifically an output clock cycle is produced after (REG_DIV divisor)/2
 * or (REG_DIV divisor + 1)/2 input cycles, the latter taking effect when top
 * bit of the 32-bit accumulator is set. The accumulator is incremented each
 * produced output cycle, by the value from either REG_INC1 or REG_INC2, which
 * of the two is selected depending again on the accumulator's current top bit.
 *
 * Because the NCO hardware implements counting of input clock cycles in part
 * in a Galois linear-feedback shift register, the higher bits of divisor
 * are programmed into REG_DIV by picking an appropriate LFSR state. See
 * applnco_compute_tables/applnco_div_translate for details on this.
 */

#define LFSR_POLY	0xa01
#define LFSR_INIT	0x7ff
#define LFSR_LEN	11
#define LFSR_PERIOD	((1 << LFSR_LEN) - 1)
#define LFSR_TBLSIZE	(1 << LFSR_LEN)

/* The minimal attainable coarse divisor (first value in table) */
#define COARSE_DIV_OFFSET 2

struct applnco_tables {
	u16 fwd[LFSR_TBLSIZE];
	u16 inv[LFSR_TBLSIZE];
};

struct applnco_channel {
	void __iomem *base;
	struct applnco_tables *tbl;
	struct clk_hw hw;

	spinlock_t lock;
};

#define to_applnco_channel(_hw) container_of(_hw, struct applnco_channel, hw)

static void applnco_enable_nolock(struct clk_hw *hw)
{
	struct applnco_channel *chan = to_applnco_channel(hw);
	u32 val;

	val = readl_relaxed(chan->base + REG_CTRL);
	writel_relaxed(val | CTRL_ENABLE, chan->base + REG_CTRL);
}

static void applnco_disable_nolock(struct clk_hw *hw)
{
	struct applnco_channel *chan = to_applnco_channel(hw);
	u32 val;

	val = readl_relaxed(chan->base + REG_CTRL);
	writel_relaxed(val & ~CTRL_ENABLE, chan->base + REG_CTRL);
}

static int applnco_is_enabled(struct clk_hw *hw)
{
	struct applnco_channel *chan = to_applnco_channel(hw);

	return (readl_relaxed(chan->base + REG_CTRL) & CTRL_ENABLE) != 0;
}

static void applnco_compute_tables(struct applnco_tables *tbl)
{
	int i;
	u32 state = LFSR_INIT;

	/*
	 * Go through the states of a Galois LFSR and build
	 * a coarse divisor translation table.
	 */
	for (i = LFSR_PERIOD; i > 0; i--) {
		if (state & 1)
			state = (state >> 1) ^ (LFSR_POLY >> 1);
		else
			state = (state >> 1);
		tbl->fwd[i] = state;
		tbl->inv[state] = i;
	}

	/* Zero value is special-cased */
	tbl->fwd[0] = 0;
	tbl->inv[0] = 0;
}

static bool applnco_div_out_of_range(unsigned int div)
{
	unsigned int coarse = div / 4;

	return coarse < COARSE_DIV_OFFSET ||
		coarse >= COARSE_DIV_OFFSET + LFSR_TBLSIZE;
}

static u32 applnco_div_translate(struct applnco_tables *tbl, unsigned int div)
{
	unsigned int coarse = div / 4;

	if (WARN_ON(applnco_div_out_of_range(div)))
		return 0;

	return FIELD_PREP(DIV_COARSE, tbl->fwd[coarse - COARSE_DIV_OFFSET]) |
			FIELD_PREP(DIV_FINE, div % 4);
}

static unsigned int applnco_div_translate_inv(struct applnco_tables *tbl, u32 regval)
{
	unsigned int coarse, fine;

	coarse = tbl->inv[FIELD_GET(DIV_COARSE, regval)] + COARSE_DIV_OFFSET;
	fine = FIELD_GET(DIV_FINE, regval);

	return coarse * 4 + fine;
}

static int applnco_set_rate(struct clk_hw *hw, unsigned long rate,
				unsigned long parent_rate)
{
	struct applnco_channel *chan = to_applnco_channel(hw);
	unsigned long flags;
	u32 div, inc1, inc2;
	bool was_enabled;

	div = 2 * parent_rate / rate;
	inc1 = 2 * parent_rate - div * rate;
	inc2 = inc1 - rate;

	if (applnco_div_out_of_range(div))
		return -EINVAL;

	div = applnco_div_translate(chan->tbl, div);

	spin_lock_irqsave(&chan->lock, flags);
	was_enabled = applnco_is_enabled(hw);
	applnco_disable_nolock(hw);

	writel_relaxed(div,  chan->base + REG_DIV);
	writel_relaxed(inc1, chan->base + REG_INC1);
	writel_relaxed(inc2, chan->base + REG_INC2);

	/* Presumably a neutral initial value for accumulator */
	writel_relaxed(1 << 31, chan->base + REG_ACCINIT);

	if (was_enabled)
		applnco_enable_nolock(hw);
	spin_unlock_irqrestore(&chan->lock, flags);

	return 0;
}

static unsigned long applnco_recalc_rate(struct clk_hw *hw,
				unsigned long parent_rate)
{
	struct applnco_channel *chan = to_applnco_channel(hw);
	u32 div, inc1, inc2, incbase;

	div = applnco_div_translate_inv(chan->tbl,
			readl_relaxed(chan->base + REG_DIV));

	inc1 = readl_relaxed(chan->base + REG_INC1);
	inc2 = readl_relaxed(chan->base + REG_INC2);

	/*
	 * We don't support wraparound of accumulator
	 * nor the edge case of both increments being zero
	 */
	if (inc1 >= (1 << 31) || inc2 < (1 << 31) || (inc1 == 0 && inc2 == 0))
		return 0;

	/* Scale both sides of division by incbase to maintain precision */
	incbase = inc1 - inc2;

	return div64_u64(((u64) parent_rate) * 2 * incbase,
			((u64) div) * incbase + inc1);
}

static long applnco_round_rate(struct clk_hw *hw, unsigned long rate,
				unsigned long *parent_rate)
{
	unsigned long lo = *parent_rate / (COARSE_DIV_OFFSET + LFSR_TBLSIZE) + 1;
	unsigned long hi = *parent_rate / COARSE_DIV_OFFSET;

	return clamp(rate, lo, hi);
}

static int applnco_enable(struct clk_hw *hw)
{
	struct applnco_channel *chan = to_applnco_channel(hw);
	unsigned long flags;

	spin_lock_irqsave(&chan->lock, flags);
	applnco_enable_nolock(hw);
	spin_unlock_irqrestore(&chan->lock, flags);

	return 0;
}

static void applnco_disable(struct clk_hw *hw)
{
	struct applnco_channel *chan = to_applnco_channel(hw);
	unsigned long flags;

	spin_lock_irqsave(&chan->lock, flags);
	applnco_disable_nolock(hw);
	spin_unlock_irqrestore(&chan->lock, flags);
}

static const struct clk_ops applnco_ops = {
	.set_rate = applnco_set_rate,
	.recalc_rate = applnco_recalc_rate,
	.round_rate = applnco_round_rate,
	.enable = applnco_enable,
	.disable = applnco_disable,
	.is_enabled = applnco_is_enabled,
};

static int applnco_probe(struct platform_device *pdev)
{
	struct device_node *np = pdev->dev.of_node;
	struct clk_parent_data pdata = { .index = 0 };
	struct clk_init_data init;
	struct clk_hw_onecell_data *onecell_data;
	void __iomem *base;
	struct resource *res;
	struct applnco_tables *tbl;
	unsigned int nchannels;
	int ret, i;

	base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
	if (IS_ERR(base))
		return PTR_ERR(base);

	if (resource_size(res) < NCO_CHANNEL_REGSIZE)
		return -EINVAL;
	nchannels = (resource_size(res) - NCO_CHANNEL_REGSIZE)
			/ NCO_CHANNEL_STRIDE + 1;

	onecell_data = devm_kzalloc(&pdev->dev, struct_size(onecell_data, hws,
							nchannels), GFP_KERNEL);
	if (!onecell_data)
		return -ENOMEM;
	onecell_data->num = nchannels;

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

	for (i = 0; i < nchannels; i++) {
		struct applnco_channel *chan;

		chan = devm_kzalloc(&pdev->dev, sizeof(*chan), GFP_KERNEL);
		if (!chan)
			return -ENOMEM;
		chan->base = base + NCO_CHANNEL_STRIDE * i;
		chan->tbl = tbl;
		spin_lock_init(&chan->lock);

		memset(&init, 0, sizeof(init));
		init.name = devm_kasprintf(&pdev->dev, GFP_KERNEL,
						"%s-%d", np->name, i);
		init.ops = &applnco_ops;
		init.parent_data = &pdata;
		init.num_parents = 1;
		init.flags = 0;

		chan->hw.init = &init;
		ret = devm_clk_hw_register(&pdev->dev, &chan->hw);
		if (ret)
			return ret;

		onecell_data->hws[i] = &chan->hw;
	}

	return devm_of_clk_add_hw_provider(&pdev->dev, of_clk_hw_onecell_get,
							onecell_data);
}

static const struct of_device_id applnco_ids[] = {
	{ .compatible = "apple,nco" },
	{ }
};
MODULE_DEVICE_TABLE(of, applnco_ids);

static struct platform_driver applnco_driver = {
	.driver = {
		.name = "apple-nco",
		.of_match_table = applnco_ids,
	},
	.probe = applnco_probe,
};
module_platform_driver(applnco_driver);

MODULE_AUTHOR("Martin Povišer <povik+lin@cutebit.org>");
MODULE_DESCRIPTION("Clock driver for NCO blocks on Apple SoCs");
MODULE_LICENSE("GPL");