[PATCH v9 05/21] clk: Add K210 pll support

[Sean Anderson <seanga2@gmail.com>]

This pll code is primarily based on the code from the kendryte standalone
sdk in lib/drivers/sysctl.c. k210_pll_calc_config is roughly analogous to
the algorithm used to set the pll frequency, but it has been completely
rewritten to be fixed-point based.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
CC: Lukasz Majewski <lukma@denx.de>
---

Changes in v8:
- Rename k210_pll_params to k210_pll_config to avoid a name conflict with the
  rest of the clock code
Changes in v6:
- Reformat code to reduce checkpatch errors

Changes in v5:
- Add function to register from a struct

Changes in v4:
- Rename the reference clock to "divider clock", and input clock to "reference
  clock" to match the upstream documentation.
- Add a test for calc_params. This currently resides in test/dm, but perhaps it
  should be moved to its own directory.
- Update MAINTAINERS
- Update copyright
- Lint

Changes in v3:
- Add an option to not include support for setting the pll rate. This saves
  around 1K in the final executable.
- Remove udelays to suppress warnings
- Bypass PLL after enabling, instead of before
- Check if the PLL is enabled already before doing a reset
- Fix bug with locked mask

Changes in v2:
- Rename driver to "k210_clk_pll"
- Add additional in-line documentation on algorithm and PLLs
- Restrict the range of internal VCO and reference frequencies
- Don't load driver before relocation
- Remove spurious references to mach-k210

 drivers/clk/Kconfig           |   1 +
 drivers/clk/Makefile          |   1 +
 drivers/clk/kendryte/Kconfig  |  12 +
 drivers/clk/kendryte/Makefile |   1 +
 drivers/clk/kendryte/pll.c    | 601 ++++++++++++++++++++++++++++++++++
 include/kendryte/pll.h        |  57 ++++
 include/test/export.h         |  16 +
 test/dm/Makefile              |   1 +
 test/dm/k210_pll.c            |  96 ++++++
 9 files changed, 786 insertions(+)
 create mode 100644 drivers/clk/kendryte/Kconfig
 create mode 100644 drivers/clk/kendryte/Makefile
 create mode 100644 drivers/clk/kendryte/pll.c
 create mode 100644 include/kendryte/pll.h
 create mode 100644 include/test/export.h
 create mode 100644 test/dm/k210_pll.c

diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 1992d4a4b4..fb8335267b 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -155,6 +155,7 @@ source "drivers/clk/analogbits/Kconfig"
 source "drivers/clk/at91/Kconfig"
 source "drivers/clk/exynos/Kconfig"
 source "drivers/clk/imx/Kconfig"
+source "drivers/clk/kendryte/Kconfig"
 source "drivers/clk/meson/Kconfig"
 source "drivers/clk/mvebu/Kconfig"
 source "drivers/clk/owl/Kconfig"
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index e01783391d..d911954581 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -27,6 +27,7 @@ obj-$(CONFIG_CLK_BOSTON) += clk_boston.o
 obj-$(CONFIG_CLK_EXYNOS) += exynos/
 obj-$(CONFIG_$(SPL_TPL_)CLK_INTEL) += intel/
 obj-$(CONFIG_CLK_HSDK) += clk-hsdk-cgu.o
+obj-$(CONFIG_CLK_K210) += kendryte/
 obj-$(CONFIG_CLK_MPC83XX) += mpc83xx_clk.o
 obj-$(CONFIG_CLK_OWL) += owl/
 obj-$(CONFIG_CLK_RENESAS) += renesas/
diff --git a/drivers/clk/kendryte/Kconfig b/drivers/clk/kendryte/Kconfig
new file mode 100644
index 0000000000..7b69c8afaf
--- /dev/null
+++ b/drivers/clk/kendryte/Kconfig
@@ -0,0 +1,12 @@
+config CLK_K210
+	bool "Clock support for Kendryte K210"
+	depends on CLK && CLK_CCF
+	help
+	  This enables support clock driver for Kendryte K210 platforms.
+
+config CLK_K210_SET_RATE
+	bool "Enable setting the Kendryte K210 PLL rate"
+	depends on CLK_K210
+	help
+	  Add functionality to calculate new rates for K210 PLLs. Enabling this
+	  feature adds around 1K to U-Boot's final size.
diff --git a/drivers/clk/kendryte/Makefile b/drivers/clk/kendryte/Makefile
new file mode 100644
index 0000000000..c56d93ea1c
--- /dev/null
+++ b/drivers/clk/kendryte/Makefile
@@ -0,0 +1 @@
+obj-y += pll.o
diff --git a/drivers/clk/kendryte/pll.c b/drivers/clk/kendryte/pll.c
new file mode 100644
index 0000000000..2c5d5b8857
--- /dev/null
+++ b/drivers/clk/kendryte/pll.c
@@ -0,0 +1,601 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019-20 Sean Anderson <seanga2@gmail.com>
+ */
+#include <kendryte/pll.h>
+
+#define LOG_CATEGORY UCLASS_CLK
+#include <asm/io.h>
+/* For DIV_ROUND_DOWN_ULL, defined in linux/kernel.h */
+#include <div64.h>
+#include <dt-bindings/clock/k210-sysctl.h>
+#include <linux/bitfield.h>
+#include <linux/clk-provider.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <log.h>
+#include <serial.h>
+
+#define CLK_K210_PLL "k210_clk_pll"
+
+#ifdef CONFIG_CLK_K210_SET_RATE
+static int k210_pll_enable(struct clk *clk);
+static int k210_pll_disable(struct clk *clk);
+
+/*
+ * The PLL included with the Kendryte K210 appears to be a True Circuits, Inc.
+ * General-Purpose PLL. The logical layout of the PLL with internal feedback is
+ * approximately the following:
+ *
+ *  +---------------+
+ *  |reference clock|
+ *  +---------------+
+ *          |
+ *          v
+ *        +--+
+ *        |/r|
+ *        +--+
+ *          |
+ *          v
+ *   +-------------+
+ *   |divided clock|
+ *   +-------------+
+ *          |
+ *          v
+ *  +--------------+
+ *  |phase detector|<---+
+ *  +--------------+    |
+ *          |           |
+ *          v   +--------------+
+ *        +---+ |feedback clock|
+ *        |VCO| +--------------+
+ *        +---+         ^
+ *          |    +--+   |
+ *          +--->|/f|---+
+ *          |    +--+
+ *          v
+ *        +---+
+ *        |/od|
+ *        +---+
+ *          |
+ *          v
+ *       +------+
+ *       |output|
+ *       +------+
+ *
+ * The k210 PLLs have three factors: r, f, and od. Because of the feedback mode,
+ * the effect of the division by f is to multiply the input frequency. The
+ * equation for the output rate is
+ *   rate = (rate_in * f) / (r * od).
+ * Moving knowns to one side of the equation, we get
+ *   rate / rate_in = f / (r * od)
+ * Rearranging slightly,
+ *   abs_error = abs((rate / rate_in) - (f / (r * od))).
+ * To get relative, error, we divide by the expected ratio
+ *   error = abs((rate / rate_in) - (f / (r * od))) / (rate / rate_in).
+ * Simplifying,
+ *   error = abs(1 - f / (r * od)) / (rate / rate_in)
+ *   error = abs(1 - (f * rate_in) / (r * od * rate))
+ * Using the constants ratio = rate / rate_in and inv_ratio = rate_in / rate,
+ *   error = abs((f * inv_ratio) / (r * od) - 1)
+ * This is the error used in evaluating parameters.
+ *
+ * r and od are four bits each, while f is six bits. Because r and od are
+ * multiplied together, instead of the full 256 values possible if both bits
+ * were used fully, there are only 97 distinct products. Combined with f, there
+ * are 6208 theoretical settings for the PLL. However, most of these settings
+ * can be ruled out immediately because they do not have the correct ratio.
+ *
+ * In addition to the constraint of approximating the desired ratio, parameters
+ * must also keep internal pll frequencies within acceptable ranges. The divided
+ * clock's minimum and maximum frequencies have a ratio of around 128.  This
+ * leaves fairly substantial room to work with, especially since the only
+ * affected parameter is r. The VCO's minimum and maximum frequency have a ratio
+ * of 5, which is considerably more restrictive.
+ *
+ * The r and od factors are stored in a table. This is to make it easy to find
+ * the next-largest product. Some products have multiple factorizations, but
+ * only when one factor has at least a 2.5x ratio to the factors of the other
+ * factorization. This is because any smaller ratio would not make a difference
+ * when ensuring the VCO's frequency is within spec.
+ *
+ * Throughout the calculation function, fixed point arithmetic is used. Because
+ * the range of rate and rate_in may be up to 1.75 GHz, or around 2^30, 64-bit
+ * 32.32 fixed-point numbers are used to represent ratios. In general, to
+ * implement division, the numerator is first multiplied by 2^32. This gives a
+ * result where the whole number part is in the upper 32 bits, and the fraction
+ * is in the lower 32 bits.
+ *
+ * In general, rounding is done to the closest integer. This helps find the best
+ * approximation for the ratio. Rounding in one direction (e.g down) could cause
+ * the function to miss a better ratio with one of the parameters increased by
+ * one.
+ */
+
+/*
+ * The factors table was generated with the following python code:
+ *
+ * def p(x, y):
+ *    return (1.0*x/y > 2.5) or (1.0*y/x > 2.5)
+ *
+ * factors = {}
+ * for i in range(1, 17):
+ *    for j in range(1, 17):
+ *       fs = factors.get(i*j) or []
+ *       if fs == [] or all([
+ *             (p(i, x) and p(i, y)) or (p(j, x) and p(j, y))
+ *             for (x, y) in fs]):
+ *          fs.append((i, j))
+ *          factors[i*j] = fs
+ *
+ * for k, l in sorted(factors.items()):
+ *    for v in l:
+ *       print("PACK(%s, %s)," % v)
+ */
+#define PACK(r, od) (((((r) - 1) & 0xF) << 4) | (((od) - 1) & 0xF))
+#define UNPACK_R(val) ((((val) >> 4) & 0xF) + 1)
+#define UNPACK_OD(val) (((val) & 0xF) + 1)
+static const u8 factors[] = {
+	PACK(1, 1),
+	PACK(1, 2),
+	PACK(1, 3),
+	PACK(1, 4),
+	PACK(1, 5),
+	PACK(1, 6),
+	PACK(1, 7),
+	PACK(1, 8),
+	PACK(1, 9),
+	PACK(3, 3),
+	PACK(1, 10),
+	PACK(1, 11),
+	PACK(1, 12),
+	PACK(3, 4),
+	PACK(1, 13),
+	PACK(1, 14),
+	PACK(1, 15),
+	PACK(3, 5),
+	PACK(1, 16),
+	PACK(4, 4),
+	PACK(2, 9),
+	PACK(2, 10),
+	PACK(3, 7),
+	PACK(2, 11),
+	PACK(2, 12),
+	PACK(5, 5),
+	PACK(2, 13),
+	PACK(3, 9),
+	PACK(2, 14),
+	PACK(2, 15),
+	PACK(2, 16),
+	PACK(3, 11),
+	PACK(5, 7),
+	PACK(3, 12),
+	PACK(3, 13),
+	PACK(4, 10),
+	PACK(3, 14),
+	PACK(4, 11),
+	PACK(3, 15),
+	PACK(3, 16),
+	PACK(7, 7),
+	PACK(5, 10),
+	PACK(4, 13),
+	PACK(6, 9),
+	PACK(5, 11),
+	PACK(4, 14),
+	PACK(4, 15),
+	PACK(7, 9),
+	PACK(4, 16),
+	PACK(5, 13),
+	PACK(6, 11),
+	PACK(5, 14),
+	PACK(6, 12),
+	PACK(5, 15),
+	PACK(7, 11),
+	PACK(6, 13),
+	PACK(5, 16),
+	PACK(9, 9),
+	PACK(6, 14),
+	PACK(8, 11),
+	PACK(6, 15),
+	PACK(7, 13),
+	PACK(6, 16),
+	PACK(7, 14),
+	PACK(9, 11),
+	PACK(10, 10),
+	PACK(8, 13),
+	PACK(7, 15),
+	PACK(9, 12),
+	PACK(10, 11),
+	PACK(7, 16),
+	PACK(9, 13),
+	PACK(8, 15),
+	PACK(11, 11),
+	PACK(9, 14),
+	PACK(8, 16),
+	PACK(10, 13),
+	PACK(11, 12),
+	PACK(9, 15),
+	PACK(10, 14),
+	PACK(11, 13),
+	PACK(9, 16),
+	PACK(10, 15),
+	PACK(11, 14),
+	PACK(12, 13),
+	PACK(10, 16),
+	PACK(11, 15),
+	PACK(12, 14),
+	PACK(13, 13),
+	PACK(11, 16),
+	PACK(12, 15),
+	PACK(13, 14),
+	PACK(12, 16),
+	PACK(13, 15),
+	PACK(14, 14),
+	PACK(13, 16),
+	PACK(14, 15),
+	PACK(14, 16),
+	PACK(15, 15),
+	PACK(15, 16),
+	PACK(16, 16),
+};
+
+TEST_STATIC int k210_pll_calc_config(u32 rate, u32 rate_in,
+				     struct k210_pll_config *best)
+{
+	int i;
+	s64 error, best_error;
+	u64 ratio, inv_ratio; /* fixed point 32.32 ratio of the rates */
+	u64 max_r;
+	u64 r, f, od;
+
+	/*
+	 * Can't go over 1.75 GHz or under 21.25 MHz due to limitations on the
+	 * VCO frequency. These are not the same limits as below because od can
+	 * reduce the output frequency by 16.
+	 */
+	if (rate > 1750000000 || rate < 21250000)
+		return -EINVAL;
+
+	/* Similar restrictions on the input rate */
+	if (rate_in > 1750000000 || rate_in < 13300000)
+		return -EINVAL;
+
+	ratio = DIV_ROUND_CLOSEST_ULL((u64)rate << 32, rate_in);
+	inv_ratio = DIV_ROUND_CLOSEST_ULL((u64)rate_in << 32, rate);
+	/* Can't increase by more than 64 or reduce by more than 256 */
+	if (rate > rate_in && ratio > (64ULL << 32))
+		return -EINVAL;
+	else if (rate <= rate_in && inv_ratio > (256ULL << 32))
+		return -EINVAL;
+
+	/*
+	 * The divided clock (rate_in / r) must stay between 1.75 GHz and 13.3
+	 * MHz. There is no minimum, since the only way to get a higher input
+	 * clock than 26 MHz is to use a clock generated by a PLL. Because PLLs
+	 * cannot output frequencies greater than 1.75 GHz, the minimum would
+	 * never be greater than one.
+	 */
+	max_r = DIV_ROUND_DOWN_ULL(rate_in, 13300000);
+
+	/* Variables get immediately incremented, so start at -1th iteration */
+	i = -1;
+	f = 0;
+	r = 0;
+	od = 0;
+	best_error = S64_MAX;
+	error = best_error;
+	/* do-while here so we always try@least one ratio */
+	do {
+		/*
+		 * Whether we swapped r and od while enforcing frequency limits
+		 */
+		bool swapped = false;
+		u64 last_od = od;
+		u64 last_r = r;
+
+		/*
+		 * Try the next largest value for f (or r and od) and
+		 * recalculate the other parameters based on that
+		 */
+		if (rate > rate_in) {
+			/*
+			 * Skip factors of the same product if we already tried
+			 * out that product
+			 */
+			do {
+				i++;
+				r = UNPACK_R(factors[i]);
+				od = UNPACK_OD(factors[i]);
+			} while (i + 1 < ARRAY_SIZE(factors) &&
+				 r * od == last_r * last_od);
+
+			/* Round close */
+			f = (r * od * ratio + BIT(31)) >> 32;
+			if (f > 64)
+				f = 64;
+		} else {
+			u64 tmp = ++f * inv_ratio;
+			bool round_up = !!(tmp & BIT(31));
+			u32 goal = (tmp >> 32) + round_up;
+			u32 err, last_err;
+
+			/* Get the next r/od pair in factors */
+			while (r * od < goal && i + 1 < ARRAY_SIZE(factors)) {
+				i++;
+				r = UNPACK_R(factors[i]);
+				od = UNPACK_OD(factors[i]);
+			}
+
+			/*
+			 * This is a case of double rounding. If we rounded up
+			 * above, we need to round down (in cases of ties) here.
+			 * This prevents off-by-one errors resulting from
+			 * choosing X+2 over X when X.Y rounds up to X+1 and
+			 * there is no r * od = X+1. For the converse, when X.Y
+			 * is rounded down to X, we should choose X+1 over X-1.
+			 */
+			err = abs(r * od - goal);
+			last_err = abs(last_r * last_od - goal);
+			if (last_err < err || (round_up && last_err == err)) {
+				i--;
+				r = last_r;
+				od = last_od;
+			}
+		}
+
+		/*
+		 * Enforce limits on internal clock frequencies. If we
+		 * aren't in spec, try swapping r and od. If everything is
+		 * in-spec, calculate the relative error.
+		 */
+		while (true) {
+			/*
+			 * Whether the intermediate frequencies are out-of-spec
+			 */
+			bool out_of_spec = false;
+
+			if (r > max_r) {
+				out_of_spec = true;
+			} else {
+				/*
+				 * There is no way to only divide once; we need
+				 * to examine the frequency with and without the
+				 * effect of od.
+				 */
+				u64 vco = DIV_ROUND_CLOSEST_ULL(rate_in * f, r);
+
+				if (vco > 1750000000 || vco < 340000000)
+					out_of_spec = true;
+			}
+
+			if (out_of_spec) {
+				if (!swapped) {
+					u64 tmp = r;
+
+					r = od;
+					od = tmp;
+					swapped = true;
+					continue;
+				} else {
+					/*
+					 * Try looking ahead to see if there are
+					 * additional factors for the same
+					 * product.
+					 */
+					if (i + 1 < ARRAY_SIZE(factors)) {
+						u64 new_r, new_od;
+
+						i++;
+						new_r = UNPACK_R(factors[i]);
+						new_od = UNPACK_OD(factors[i]);
+						if (r * od == new_r * new_od) {
+							r = new_r;
+							od = new_od;
+							swapped = false;
+							continue;
+						}
+						i--;
+					}
+					break;
+				}
+			}
+
+			error = DIV_ROUND_CLOSEST_ULL(f * inv_ratio, r * od);
+			/* The lower 16 bits are spurious */
+			error = abs((error - BIT(32))) >> 16;
+
+			if (error < best_error) {
+				best->r = r;
+				best->f = f;
+				best->od = od;
+				best_error = error;
+			}
+			break;
+		}
+	} while (f < 64 && i + 1 < ARRAY_SIZE(factors) && error != 0);
+
+	if (best_error == S64_MAX)
+		return -EINVAL;
+
+	log_debug("best error %lld\n", best_error);
+	return 0;
+}
+
+static ulong k210_pll_set_rate(struct clk *clk, ulong rate)
+{
+	int err;
+	long long rate_in = clk_get_parent_rate(clk);
+	struct k210_pll_config config = {};
+	struct k210_pll *pll = to_k210_pll(clk);
+	u32 reg;
+
+	if (rate_in < 0)
+		return rate_in;
+
+	log_debug("Calculating parameters with rate=%lu and rate_in=%lld\n",
+		  rate, rate_in);
+	err = k210_pll_calc_config(rate, rate_in, &config);
+	if (err)
+		return err;
+	log_debug("Got r=%u f=%u od=%u\n", config.r, config.f, config.od);
+
+	/*
+	 * Don't use clk_disable as it might not actually disable the pll due to
+	 * refcounting
+	 */
+	k210_pll_disable(clk);
+
+	reg = readl(pll->reg);
+	reg &= ~K210_PLL_CLKR
+	    &  ~K210_PLL_CLKF
+	    &  ~K210_PLL_CLKOD
+	    &  ~K210_PLL_BWADJ;
+	reg |= FIELD_PREP(K210_PLL_CLKR, config.r - 1)
+	    |  FIELD_PREP(K210_PLL_CLKF, config.f - 1)
+	    |  FIELD_PREP(K210_PLL_CLKOD, config.od - 1)
+	    |  FIELD_PREP(K210_PLL_BWADJ, config.f - 1);
+	writel(reg, pll->reg);
+
+	err = k210_pll_enable(clk);
+	if (err)
+		return err;
+
+	serial_setbrg();
+	return clk_get_rate(clk);
+}
+#endif /* CONFIG_CLK_K210_SET_RATE */
+
+static ulong k210_pll_get_rate(struct clk *clk)
+{
+	long long rate_in = clk_get_parent_rate(clk);
+	struct k210_pll *pll = to_k210_pll(clk);
+	u64 r, f, od;
+	u32 reg = readl(pll->reg);
+
+	if (rate_in < 0 || (reg & K210_PLL_BYPASS))
+		return rate_in;
+
+	if (!(reg & K210_PLL_PWRD))
+		return 0;
+
+	r = FIELD_GET(K210_PLL_CLKR, reg) + 1;
+	f = FIELD_GET(K210_PLL_CLKF, reg) + 1;
+	od = FIELD_GET(K210_PLL_CLKOD, reg) + 1;
+
+	return DIV_ROUND_DOWN_ULL(((u64)rate_in) * f, r * od);
+}
+
+/*
+ * Wait for the PLL to be locked. If the PLL is not locked, try clearing the
+ * slip before retrying
+ */
+static void k210_pll_waitfor_lock(struct k210_pll *pll)
+{
+	u32 mask = GENMASK(pll->width - 1, 0) << pll->shift;
+
+	while (true) {
+		u32 reg = readl(pll->lock);
+
+		if ((reg & mask) == mask)
+			break;
+
+		reg |= BIT(pll->shift + K210_PLL_CLEAR_SLIP);
+		writel(reg, pll->lock);
+	}
+}
+
+/* Adapted from sysctl_pll_enable */
+static int k210_pll_enable(struct clk *clk)
+{
+	struct k210_pll *pll = to_k210_pll(clk);
+	u32 reg = readl(pll->reg);
+
+	if ((reg | K210_PLL_PWRD) && !(reg | K210_PLL_RESET))
+		return 0;
+
+	reg |= K210_PLL_PWRD;
+	writel(reg, pll->reg);
+
+	/* Ensure reset is low before asserting it */
+	reg &= ~K210_PLL_RESET;
+	writel(reg, pll->reg);
+	reg |= K210_PLL_RESET;
+	writel(reg, pll->reg);
+	nop();
+	nop();
+	reg &= ~K210_PLL_RESET;
+	writel(reg, pll->reg);
+
+	k210_pll_waitfor_lock(pll);
+
+	reg &= ~K210_PLL_BYPASS;
+	writel(reg, pll->reg);
+
+	return 0;
+}
+
+static int k210_pll_disable(struct clk *clk)
+{
+	struct k210_pll *pll = to_k210_pll(clk);
+	u32 reg = readl(pll->reg);
+
+	/*
+	 * Bypassing before powering off is important so child clocks don't stop
+	 * working. This is especially important for pll0, the indirect parent
+	 * of the cpu clock.
+	 */
+	reg |= K210_PLL_BYPASS;
+	writel(reg, pll->reg);
+
+	reg &= ~K210_PLL_PWRD;
+	writel(reg, pll->reg);
+	return 0;
+}
+
+const struct clk_ops k210_pll_ops = {
+	.get_rate = k210_pll_get_rate,
+#ifdef CONFIG_CLK_K210_SET_RATE
+	.set_rate = k210_pll_set_rate,
+#endif
+	.enable = k210_pll_enable,
+	.disable = k210_pll_disable,
+};
+
+struct clk *k210_register_pll_struct(const char *name, const char *parent_name,
+				     struct k210_pll *pll)
+{
+	int ret;
+	struct clk *clk = &pll->clk;
+
+	ret = clk_register(clk, CLK_K210_PLL, name, parent_name);
+	if (ret)
+		return ERR_PTR(ret);
+	return clk;
+}
+
+struct clk *k210_register_pll(const char *name, const char *parent_name,
+			      void __iomem *reg, void __iomem *lock, u8 shift,
+			      u8 width)
+{
+	struct clk *clk;
+	struct k210_pll *pll;
+
+	pll = kzalloc(sizeof(*pll), GFP_KERNEL);
+	if (!pll)
+		return ERR_PTR(-ENOMEM);
+	pll->reg = reg;
+	pll->lock = lock;
+	pll->shift = shift;
+	pll->width = width;
+
+	clk = k210_register_pll_struct(name, parent_name, pll);
+	if (IS_ERR(clk))
+		kfree(pll);
+	return clk;
+}
+
+U_BOOT_DRIVER(k210_pll) = {
+	.name	= CLK_K210_PLL,
+	.id	= UCLASS_CLK,
+	.ops	= &k210_pll_ops,
+};
diff --git a/include/kendryte/pll.h b/include/kendryte/pll.h
new file mode 100644
index 0000000000..c8e3200799
--- /dev/null
+++ b/include/kendryte/pll.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2019-20 Sean Anderson <seanga2@gmail.com>
+ */
+#ifndef K210_PLL_H
+#define K210_PLL_H
+
+#include <clk.h>
+#include <test/export.h>
+
+#define K210_PLL_CLKR GENMASK(3, 0)
+#define K210_PLL_CLKF GENMASK(9, 4)
+#define K210_PLL_CLKOD GENMASK(13, 10) /* Output Divider */
+#define K210_PLL_BWADJ GENMASK(19, 14) /* BandWidth Adjust */
+#define K210_PLL_RESET BIT(20)
+#define K210_PLL_PWRD BIT(21) /* PoWeReD */
+#define K210_PLL_INTFB BIT(22) /* Internal FeedBack */
+#define K210_PLL_BYPASS BIT(23)
+#define K210_PLL_TEST BIT(24)
+#define K210_PLL_EN BIT(25)
+#define K210_PLL_TEST_EN BIT(26)
+
+#define K210_PLL_LOCK 0
+#define K210_PLL_CLEAR_SLIP 2
+#define K210_PLL_TEST_OUT 3
+
+struct k210_pll {
+	struct clk clk;
+	void __iomem *reg; /* Base PLL register */
+	void __iomem *lock; /* Common PLL lock register */
+	u8 shift; /* Offset of bits in lock register */
+	u8 width; /* Width of lock bits to test against */
+};
+
+#define to_k210_pll(_clk) container_of(_clk, struct k210_pll, clk)
+
+struct k210_pll_config {
+	u8 r;
+	u8 f;
+	u8 od;
+};
+
+#ifdef CONFIG_UNIT_TEST
+TEST_STATIC int k210_pll_calc_config(u32 rate, u32 rate_in,
+				     struct k210_pll_config *best);
+#define nop()
+#endif
+
+extern const struct clk_ops k210_pll_ops;
+
+struct clk *k210_register_pll_struct(const char *name, const char *parent_name,
+				     struct k210_pll *pll);
+struct clk *k210_register_pll(const char *name, const char *parent_name,
+			      void __iomem *reg, void __iomem *lock, u8 shift,
+			      u8 width);
+
+#endif /* K210_PLL_H */
diff --git a/include/test/export.h b/include/test/export.h
new file mode 100644
index 0000000000..afc755a8ff
--- /dev/null
+++ b/include/test/export.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2020 Sean Anderson <seanga2@gmail.com>
+ */
+
+#ifndef TEST_EXPORT_H
+#define TEST_EXPORT_H
+
+/* Declare something static, unless we are doing unit tests */
+#ifdef CONFIG_UNIT_TEST
+#define TEST_STATIC
+#else
+#define TEST_STATIC static
+#endif
+
+#endif /* TEST_EXPORT_H */
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 6c18fd04ce..5094a7866a 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -73,4 +73,5 @@ obj-$(CONFIG_DMA) += dma.o
 obj-$(CONFIG_DM_MDIO) += mdio.o
 obj-$(CONFIG_DM_MDIO_MUX) += mdio_mux.o
 obj-$(CONFIG_DM_RNG) += rng.o
+obj-$(CONFIG_CLK_K210_SET_RATE) += k210_pll.o
 endif
diff --git a/test/dm/k210_pll.c b/test/dm/k210_pll.c
new file mode 100644
index 0000000000..54764f269c
--- /dev/null
+++ b/test/dm/k210_pll.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Sean Anderson <seanga2@gmail.com>
+ */
+
+#include <common.h>
+/* For DIV_ROUND_DOWN_ULL, defined in linux/kernel.h */
+#include <div64.h>
+#include <dm/test.h>
+#include <kendryte/pll.h>
+#include <test/ut.h>
+
+static int dm_test_k210_pll_calc_config(u32 rate, u32 rate_in,
+					struct k210_pll_config *best)
+{
+	u64 f, r, od, max_r, inv_ratio;
+	s64 error, best_error;
+
+	best_error = S64_MAX;
+	error = best_error;
+	max_r = min(16ULL, DIV_ROUND_DOWN_ULL(rate_in, 13300000));
+	inv_ratio = DIV_ROUND_CLOSEST_ULL((u64)rate_in << 32, rate);
+
+	/* Brute force it */
+	for (r = 1; r <= max_r; r++) {
+		for (f = 1; f <= 64; f++) {
+			for (od = 1; od <= 16; od++) {
+				u64 vco = DIV_ROUND_CLOSEST_ULL(rate_in * f, r);
+
+				if (vco > 1750000000 || vco < 340000000)
+					continue;
+
+				error = DIV_ROUND_CLOSEST_ULL(f * inv_ratio,
+							      r * od);
+				/* The lower 16 bits are spurious */
+				error = abs((error - BIT(32))) >> 16;
+				if (error < best_error) {
+					best->r = r;
+					best->f = f;
+					best->od = od;
+					best_error = error;
+				}
+			}
+		}
+	}
+
+	if (best_error == S64_MAX)
+		return -EINVAL;
+	return 0;
+}
+
+static int dm_test_k210_pll_compare(struct k210_pll_config *ours,
+				    struct k210_pll_config *theirs)
+{
+	return (u32)ours->f * theirs->r * theirs->od !=
+	       (u32)theirs->f * ours->r * ours->od;
+}
+
+static int dm_test_k210_pll(struct unit_test_state *uts)
+{
+	struct k210_pll_config ours, theirs;
+
+	/* General range checks */
+	ut_asserteq(-EINVAL, k210_pll_calc_config(0, 26000000, &theirs));
+	ut_asserteq(-EINVAL, k210_pll_calc_config(390000000, 0, &theirs));
+	ut_asserteq(-EINVAL, k210_pll_calc_config(2000000000, 26000000,
+						  &theirs));
+	ut_asserteq(-EINVAL, k210_pll_calc_config(390000000, 2000000000,
+						  &theirs));
+	ut_asserteq(-EINVAL, k210_pll_calc_config(1500000000, 20000000,
+						  &theirs));
+
+	/* Verify we get the same output with brute-force */
+	ut_assertok(dm_test_k210_pll_calc_config(390000000, 26000000, &ours));
+	ut_assertok(k210_pll_calc_config(390000000, 26000000, &theirs));
+	ut_assertok(dm_test_k210_pll_compare(&ours, &theirs));
+
+	ut_assertok(dm_test_k210_pll_calc_config(26000000, 390000000, &ours));
+	ut_assertok(k210_pll_calc_config(26000000, 390000000, &theirs));
+	ut_assertok(dm_test_k210_pll_compare(&ours, &theirs));
+
+	ut_assertok(dm_test_k210_pll_calc_config(400000000, 26000000, &ours));
+	ut_assertok(k210_pll_calc_config(400000000, 26000000, &theirs));
+	ut_assertok(dm_test_k210_pll_compare(&ours, &theirs));
+
+	ut_assertok(dm_test_k210_pll_calc_config(27000000, 26000000, &ours));
+	ut_assertok(k210_pll_calc_config(27000000, 26000000, &theirs));
+	ut_assertok(dm_test_k210_pll_compare(&ours, &theirs));
+
+	ut_assertok(dm_test_k210_pll_calc_config(26000000, 27000000, &ours));
+	ut_assertok(k210_pll_calc_config(26000000, 27000000, &theirs));
+	ut_assertok(dm_test_k210_pll_compare(&ours, &theirs));
+
+	return 0;
+}
+DM_TEST(dm_test_k210_pll, 0);
-- 
2.26.2