[PATCH v2 0/3] Support for Apple SoCs' NCO blocks

[PATCH v2 0/3] Support for Apple SoCs' NCO blocks

[Martin Povišer]

Hi,

this is v2 of the common clock driver for NCO blocks on recent Apple SoCs.

Changes since v1:

 - drop apple,nchannels property from the binding, rely on size of the register
   range instead to gauge the number of channels
 - add a lock to guard set_rate from racing with clock disable/enable
 - add short "theory of operation" comment
 - incorporate minor changes from Rob's, Sven's and Stephen's review (thanks!)

Martin

v1: https://lore.kernel.org/linux-clk/20211214120213.15649-1-povik@protonmail.com/

Martin Povišer (3):
  dt-bindings: clock: Add Apple NCO
  clk: clk-apple-nco: Add driver for Apple NCO
  MAINTAINERS: Add clk-apple-nco under ARM/APPLE MACHINE

 .../devicetree/bindings/clock/apple,nco.yaml  |  62 ++++
 MAINTAINERS                                   |   1 +
 drivers/clk/Kconfig                           |   9 +
 drivers/clk/Makefile                          |   1 +
 drivers/clk/clk-apple-nco.c                   | 340 ++++++++++++++++++
 5 files changed, 413 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/apple,nco.yaml
 create mode 100644 drivers/clk/clk-apple-nco.c

--
2.33.0

[PATCH v2 1/3] dt-bindings: clock: Add Apple NCO

[Martin Povišer]

The NCO block found on Apple SoCs is a programmable clock generator
performing fractional division of a high frequency input clock.

Signed-off-by: Martin Povišer <povik+lin@protonmail.com>
---
 .../devicetree/bindings/clock/apple,nco.yaml  | 62 +++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/apple,nco.yaml

diff --git a/Documentation/devicetree/bindings/clock/apple,nco.yaml b/Documentation/devicetree/bindings/clock/apple,nco.yaml
new file mode 100644
index 000000000000..da56b64b8fff
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/apple,nco.yaml
@@ -0,0 +1,62 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/apple,nco.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Apple SoCs' NCO block
+
+maintainers:
+  - Martin Povišer <povik+lin@protonmail.com>
+
+description: |
+  The NCO (Numerically Controlled Oscillator) block found on Apple SoCs
+  such as the t8103 (M1) is a programmable clock generator performing
+  fractional division of a high frequency input clock.
+
+  It carries a number of independent channels and is typically used for
+  generation of audio bitclocks.
+
+properties:
+  compatible:
+    items:
+      - enum:
+        - apple,t6000-nco
+        - apple,t8103-nco
+      - const: apple,nco
+
+  clocks:
+    description:
+      Specifies the reference clock from which the output clocks
+      are derived through fractional division.
+    maxItems: 1
+
+  '#clock-cells':
+    const: 1
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - clocks
+  - '#clock-cells'
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    nco_clkref: clock-ref {
+      compatible = "fixed-clock";
+      #clock-cells = <0>;
+      clock-frequency = <900000000>;
+      clock-output-names = "nco-ref";
+    };
+
+    nco: clock-controller@23b044000 {
+      compatible = "apple,t8103-nco", "apple,nco";
+      reg = <0x3b044000 0x14000>;
+      #clock-cells = <1>;
+      clocks = <&nco_clkref>;
+    };
--
2.33.0

Re: [PATCH v2 1/3] dt-bindings: clock: Add Apple NCO

[Mark Kettenis]

> Date: Tue, 18 Jan 2022 19:21:03 +0000
> From: Martin Povišer <povik+lin@protonmail.com>
> 
> The NCO block found on Apple SoCs is a programmable clock generator
> performing fractional division of a high frequency input clock.
> 
> Signed-off-by: Martin Povišer <povik+lin@protonmail.com>

Reviewed-by: Mark Kettenis <kettenis@openbsd.org>

> ---
>  .../devicetree/bindings/clock/apple,nco.yaml  | 62 +++++++++++++++++++
>  1 file changed, 62 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/apple,nco.yaml
> 
> diff --git a/Documentation/devicetree/bindings/clock/apple,nco.yaml b/Documentation/devicetree/bindings/clock/apple,nco.yaml
> new file mode 100644
> index 000000000000..da56b64b8fff
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/apple,nco.yaml
> @@ -0,0 +1,62 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/clock/apple,nco.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Apple SoCs' NCO block
> +
> +maintainers:
> +  - Martin Povišer <povik+lin@protonmail.com>
> +
> +description: |
> +  The NCO (Numerically Controlled Oscillator) block found on Apple SoCs
> +  such as the t8103 (M1) is a programmable clock generator performing
> +  fractional division of a high frequency input clock.
> +
> +  It carries a number of independent channels and is typically used for
> +  generation of audio bitclocks.
> +
> +properties:
> +  compatible:
> +    items:
> +      - enum:
> +        - apple,t6000-nco
> +        - apple,t8103-nco
> +      - const: apple,nco
> +
> +  clocks:
> +    description:
> +      Specifies the reference clock from which the output clocks
> +      are derived through fractional division.
> +    maxItems: 1
> +
> +  '#clock-cells':
> +    const: 1
> +
> +  reg:
> +    maxItems: 1
> +
> +required:
> +  - compatible
> +  - clocks
> +  - '#clock-cells'
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    nco_clkref: clock-ref {
> +      compatible = "fixed-clock";
> +      #clock-cells = <0>;
> +      clock-frequency = <900000000>;
> +      clock-output-names = "nco-ref";
> +    };
> +
> +    nco: clock-controller@23b044000 {
> +      compatible = "apple,t8103-nco", "apple,nco";
> +      reg = <0x3b044000 0x14000>;
> +      #clock-cells = <1>;
> +      clocks = <&nco_clkref>;
> +    };
> --
> 2.33.0
> 
> 
> 

Re: [PATCH v2 1/3] dt-bindings: clock: Add Apple NCO

[Rob Herring]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1180 bytes --]

On Tue, 18 Jan 2022 19:21:03 +0000, Martin Povišer wrote:
> The NCO block found on Apple SoCs is a programmable clock generator
> performing fractional division of a high frequency input clock.
> 
> Signed-off-by: Martin Povišer <povik+lin@protonmail.com>
> ---
>  .../devicetree/bindings/clock/apple,nco.yaml  | 62 +++++++++++++++++++
>  1 file changed, 62 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/apple,nco.yaml
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:
./Documentation/devicetree/bindings/clock/apple,nco.yaml:24:9: [warning] wrong indentation: expected 10 but found 8 (indentation)

dtschema/dtc warnings/errors:

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/patch/1581480

This check can fail if there are any dependencies. The base for a patch
series is generally the most recent rc1.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit.

Re: [PATCH v2 1/3] dt-bindings: clock: Add Apple NCO

[Rob Herring]

On Tue, Jan 18, 2022 at 07:21:03PM +0000, Martin Povišer wrote:
> The NCO block found on Apple SoCs is a programmable clock generator
> performing fractional division of a high frequency input clock.
> 
> Signed-off-by: Martin Povišer <povik+lin@protonmail.com>
> ---
>  .../devicetree/bindings/clock/apple,nco.yaml  | 62 +++++++++++++++++++
>  1 file changed, 62 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/apple,nco.yaml

With the indentation fix,

Reviewed-by: Rob Herring <robh@kernel.org>

[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@protonmail.com>
---
 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@protonmail.com>");
+MODULE_DESCRIPTION("Clock driver for NCO blocks on Apple SoCs");
+MODULE_LICENSE("GPL v2");
--
2.33.0

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

[Stephen Boyd]

Quoting Martin Povišer (2022-01-18 11:21:10)
> 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>

Is this include used? If not, please drop it.

Please include kernel.h for container_of() usage.

> +#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;

Please declare the struct here.

> +
> +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];
> +};

Or put struct nco_channel here.

> +
> +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);

Define the functions here so we don't need forward declarations.

> +
> +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;

Nitpick: Newline here

> +       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)))

Maybe worth knowing which clk is out of range?

> +               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));

Is the cast necessary?

> +
> +       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);

Why is the divisor casted to 64 bits? div_u64() takes a u32 divisor so
if it's going to overflow 32 bits we're in trouble.
> +}
> +
> +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 = {

Perhaps apple_nco_ops (and apple_ prefix for the functions) so that tags
in the global namespace don't conflict.

> +       .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;

Usually it's called 'base'

> +       struct resource *regs_res;

Usually it's called '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;

Is this some sort of DIV_ROUND_UP()?

> +
> +       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;

Please add space around * above.

> +               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);

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

[Martin Povišer]

Hi Stephen,

thanks for the review.

> On 20. 1. 2022, at 6:38, Stephen Boyd <sboyd@kernel.org> wrote:
>
> Quoting Martin Povišer (2022-01-18 11:21:10)
>> 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


>> +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)))
>
> Maybe worth knowing which clk is out of range?

This can only happen when nco_div_translate is used wrong, which should never
happen with the code as-is, so I wouldn't think it is worth expanding on.

>> +
>> +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));
>
> Is the cast necessary?

Answering that prompted me to get back to reading some C specification and now
I am confident in moving away from signed types here and in nco_recalc_rate
altogether.

>>
>> +
>> +static unsigned long nco_recalc_rate(struct clk_hw *hw,
>> +                               unsigned long parent_rate)
>> +{

>> +
>> +       /* 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);
>
> Why is the divisor casted to 64 bits? div_u64() takes a u32 divisor so
> if it's going to overflow 32 bits we're in trouble.

Yeah, we need div64_u64, great you caught that.

>> +       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;
>
> Is this some sort of DIV_ROUND_UP()?

Almost. I will shop around for a macro replacement.

Martin

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

[Stephen Boyd]

Quoting Martin Povišer (2022-01-20 04:11:34)
> 
> > On 20. 1. 2022, at 6:38, Stephen Boyd <sboyd@kernel.org> wrote:
> >
> > Quoting Martin Povišer (2022-01-18 11:21:10)
> >> +
> >> +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));
> >
> > Is the cast necessary?
> 
> Answering that prompted me to get back to reading some C specification and now
> I am confident in moving away from signed types here and in nco_recalc_rate
> altogether.

Great! Operating with only unsigned types makes this easier to
understand.

> >> +       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;
> >
> > Is this some sort of DIV_ROUND_UP()?
> 
> Almost. I will shop around for a macro replacement.

Alright.

[PATCH v2 3/3] MAINTAINERS: Add clk-apple-nco under ARM/APPLE MACHINE

[Martin Povišer]

Add clk-apple-nco driver and corresponding binding schema to MAINTAINERS.

Signed-off-by: Martin Povišer <povik+lin@protonmail.com>
---
 MAINTAINERS | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 4e828542b089..9b6585717627 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1765,6 +1765,7 @@ C:        irc://irc.oftc.net/asahi-dev
 T:     git https://github.com/AsahiLinux/linux.git
 F:     Documentation/devicetree/bindings/arm/apple.yaml
 F:     Documentation/devicetree/bindings/arm/apple/*
+F:     Documentation/devicetree/bindings/clock/apple,nco.yaml
 F:     Documentation/devicetree/bindings/i2c/apple,i2c.yaml
 F:     Documentation/devicetree/bindings/interrupt-controller/apple,aic.yaml
 F:     Documentation/devicetree/bindings/mailbox/apple,mailbox.yaml
@@ -1773,6 +1774,7 @@ F:        Documentation/devicetree/bindings/pinctrl/apple,pinctrl.yaml
 F:     Documentation/devicetree/bindings/power/apple*
 F:     Documentation/devicetree/bindings/watchdog/apple,wdt.yaml
 F:     arch/arm64/boot/dts/apple/
+F:     drivers/clk/clk-apple-nco.c
 F:     drivers/i2c/busses/i2c-pasemi-core.c
 F:     drivers/i2c/busses/i2c-pasemi-platform.c
 F:     drivers/irqchip/irq-apple-aic.c
--
2.33.0