[PATCH v2 2/3] clk: clk-apple-nco: Add driver for Apple NCO

[Martin Povišer]

Add a common clock driver for NCO blocks found on Apple SoCs where they
are typically the generators of audio clocks.

Signed-off-by: Martin Povišer <povik+lin@xxxxxxxxxxxxxx>
---
 drivers/clk/Kconfig         |   9 +
 drivers/clk/Makefile        |   1 +
 drivers/clk/clk-apple-nco.c | 340 ++++++++++++++++++++++++++++++++++++
 3 files changed, 350 insertions(+)
 create mode 100644 drivers/clk/clk-apple-nco.c

diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index ad4256d54361..af4d037e18e3 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -59,6 +59,15 @@ config LMK04832
 	  Say yes here to build support for Texas Instruments' LMK04832 Ultra
 	  Low-Noise JESD204B Compliant Clock Jitter Cleaner With Dual Loop PLLs

+config COMMON_CLK_APPLE_NCO
+	bool "Clock driver for Apple SoC NCOs"
+	depends on ARCH_APPLE || COMPILE_TEST
+	default ARCH_APPLE
+	help
+	  This driver supports NCO (Numerically Controlled Oscillator) blocks
+	  found on Apple SoCs such as t8103 (M1). The blocks are typically
+	  generators of audio clocks.
+
 config COMMON_CLK_MAX77686
 	tristate "Clock driver for Maxim 77620/77686/77802 MFD"
 	depends on MFD_MAX77686 || MFD_MAX77620 || COMPILE_TEST
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 16e588630472..e95e702bdaeb 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -17,6 +17,7 @@ endif

 # hardware specific clock types
 # please keep this section sorted lexicographically by file path name
+obj-$(CONFIG_COMMON_CLK_APPLE_NCO)  	+= clk-apple-nco.o
 obj-$(CONFIG_MACH_ASM9260)		+= clk-asm9260.o
 obj-$(CONFIG_COMMON_CLK_AXI_CLKGEN)	+= clk-axi-clkgen.o
 obj-$(CONFIG_ARCH_AXXIA)		+= clk-axm5516.o
diff --git a/drivers/clk/clk-apple-nco.c b/drivers/clk/clk-apple-nco.c
new file mode 100644
index 000000000000..593f5b5ce5b7
--- /dev/null
+++ b/drivers/clk/clk-apple-nco.c
@@ -0,0 +1,340 @@
+// 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/clk-provider.h>
+#include <linux/io.h>
+#include <linux/math64.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_clk.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
+ * nco_compute_tables/nco_div_translate for details on this.
+ */
+
+struct nco_tables;
+
+struct nco_channel {
+	void __iomem *base;
+	struct nco_tables *tbl;
+	struct clk_hw hw;
+
+	spinlock_t lock;
+};
+
+#define to_nco_channel(_hw) container_of(_hw, struct nco_channel, hw)
+
+#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 nco_tables {
+	u16 fwd[LFSR_TBLSIZE];
+	u16 inv[LFSR_TBLSIZE];
+};
+
+static void nco_enable_nolock(struct clk_hw *hw);
+static void nco_disable_nolock(struct clk_hw *hw);
+static int nco_is_enabled(struct clk_hw *hw);
+
+static void nco_compute_tables(struct nco_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 nco_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 nco_div_translate(struct nco_tables *tbl, unsigned int div)
+{
+	unsigned int coarse = div / 4;
+
+	if (WARN_ON(nco_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 nco_div_translate_inv(struct nco_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 nco_set_rate(struct clk_hw *hw, unsigned long rate,
+				unsigned long parent_rate)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+	unsigned long flags;
+	u32 div;
+	s32 inc1, inc2;
+	bool was_enabled;
+
+	div = 2 * parent_rate / rate;
+	inc1 = 2 * parent_rate - div * rate;
+	inc2 = -((s32) (rate - inc1));
+
+	if (nco_div_out_of_range(div))
+		return -EINVAL;
+
+	div = nco_div_translate(chan->tbl, div);
+
+	spin_lock_irqsave(&chan->lock, flags);
+	was_enabled = nco_is_enabled(hw);
+	nco_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)
+		nco_enable_nolock(hw);
+	spin_unlock_irqrestore(&chan->lock, flags);
+
+	return 0;
+}
+
+static unsigned long nco_recalc_rate(struct clk_hw *hw,
+				unsigned long parent_rate)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+	u32 div;
+	s32 inc1, inc2, incbase;
+
+	div = nco_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 < 0 || inc2 > 0 || (inc1 == 0 && inc2 == 0))
+		return 0;
+
+	/* Scale both sides of division by incbase to maintain precision */
+	incbase = inc1 - inc2;
+
+	return div_u64(((u64) parent_rate) * 2 * incbase,
+			((u64) div) * incbase + inc1);
+}
+
+static long nco_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 void nco_enable_nolock(struct clk_hw *hw)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+	u32 val;
+
+	val = readl_relaxed(chan->base + REG_CTRL);
+	writel_relaxed(val | CTRL_ENABLE, chan->base + REG_CTRL);
+}
+
+static void nco_disable_nolock(struct clk_hw *hw)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+	u32 val;
+
+	val = readl_relaxed(chan->base + REG_CTRL);
+	writel_relaxed(val & ~CTRL_ENABLE, chan->base + REG_CTRL);
+}
+
+static int nco_is_enabled(struct clk_hw *hw)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+
+	return (readl_relaxed(chan->base + REG_CTRL) & CTRL_ENABLE) != 0;
+}
+
+static int nco_enable(struct clk_hw *hw)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+	unsigned long flags;
+
+	spin_lock_irqsave(&chan->lock, flags);
+	nco_enable_nolock(hw);
+	spin_unlock_irqrestore(&chan->lock, flags);
+
+	return 0;
+}
+
+static void nco_disable(struct clk_hw *hw)
+{
+	struct nco_channel *chan = to_nco_channel(hw);
+	unsigned long flags;
+
+	spin_lock_irqsave(&chan->lock, flags);
+	nco_disable_nolock(hw);
+	spin_unlock_irqrestore(&chan->lock, flags);
+}
+
+static const struct clk_ops nco_ops = {
+	.set_rate = nco_set_rate,
+	.recalc_rate = nco_recalc_rate,
+	.round_rate = nco_round_rate,
+	.enable = nco_enable,
+	.disable = nco_disable,
+	.is_enabled = nco_is_enabled,
+};
+
+static int apple_nco_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 *regs;
+	struct resource *regs_res;
+	struct nco_tables *tbl;
+	unsigned int nchannels;
+	int ret, i;
+
+	regs = devm_platform_get_and_ioremap_resource(pdev, 0, &regs_res);
+	if (IS_ERR(regs))
+		return PTR_ERR(regs);
+
+	if (resource_size(regs_res) < NCO_CHANNEL_REGSIZE)
+		return -EINVAL;
+	nchannels = (resource_size(regs_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;
+	nco_compute_tables(tbl);
+
+	for (i = 0; i < nchannels; i++) {
+		struct nco_channel *chan;
+
+		chan = devm_kzalloc(&pdev->dev, sizeof(*chan), GFP_KERNEL);
+		if (!chan)
+			return -ENOMEM;
+		chan->base = regs + 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 = &nco_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 apple_nco_ids[] = {
+	{ .compatible = "apple,nco" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, apple_nco_ids)
+
+static struct platform_driver apple_nco_driver = {
+	.driver = {
+		.name = "apple-nco",
+		.of_match_table = apple_nco_ids,
+	},
+	.probe = apple_nco_probe,
+};
+module_platform_driver(apple_nco_driver);
+
+MODULE_AUTHOR("Martin Povišer <povik+lin@xxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("Clock driver for NCO blocks on Apple SoCs");
+MODULE_LICENSE("GPL v2");
--
2.33.0