clk: bcm: Add driver for BCM53573 ILP clock

This clock is present on BCM53573 devices (including BCM47189) that use
Cortex-A7. ILP is a part of PMU (Power Management Unit) multi-function
device so we use syscon (and regmap) for it.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Rob Herring <robh@kernel.org>
[sboyd@codeaurora.org: Remove 0 from clk_init_data to silence sparse]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

Documentation/devicetree/bindings/clock/brcm,bcm53573-ilp.txt

+Broadcom BCM53573 ILP clock
+===========================
+
+This binding uses the common clock binding:
+    Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+This binding is used for ILP clock (sometimes referred as "slow clock")
+on Broadcom BCM53573 devices using Cortex-A7 CPU.
+
+ILP's rate has to be calculated on runtime and it depends on ALP clock
+which has to be referenced.
+
+This clock is part of PMU (Power Management Unit), a Broadcom's device
+handing power-related aspects. Its node must be sub-node of the PMU
+device.
+
+Required properties:
+- compatible: "brcm,bcm53573-ilp"
+- clocks: has to reference an ALP clock
+- #clock-cells: should be <0>
+- clock-output-names: from common clock bindings, should contain clock
+		      name
+
+Example:
+
+pmu@18012000 {
+	compatible = "simple-mfd", "syscon";
+	reg = <0x18012000 0x00001000>;
+
+	ilp {
+		compatible = "brcm,bcm53573-ilp";
+		clocks = <&alp>;
+		#clock-cells = <0>;
+		clock-output-names = "ilp";
+	};
+};

drivers/clk/bcm/Makefile

@@ -6,6 +6,7 @@ obj-$(CONFIG_CLK_BCM_KONA)	+= clk-bcm21664.o
 obj-$(CONFIG_COMMON_CLK_IPROC)	+= clk-iproc-armpll.o clk-iproc-pll.o clk-iproc-asiu.o
 obj-$(CONFIG_ARCH_BCM2835)	+= clk-bcm2835.o
 obj-$(CONFIG_ARCH_BCM2835)	+= clk-bcm2835-aux.o
+obj-$(CONFIG_ARCH_BCM_53573)	+= clk-bcm53573-ilp.o
 obj-$(CONFIG_CLK_BCM_CYGNUS)	+= clk-cygnus.o
 obj-$(CONFIG_CLK_BCM_NSP)	+= clk-nsp.o
 obj-$(CONFIG_CLK_BCM_NS2)	+= clk-ns2.o

drivers/clk/bcm/clk-bcm53573-ilp.c

+/*
+ * Copyright (C) 2016 Rafał Miłecki <rafal@milecki.pl>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/mfd/syscon.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+#define PMU_XTAL_FREQ_RATIO			0x66c
+#define  XTAL_ALP_PER_4ILP			0x00001fff
+#define  XTAL_CTL_EN				0x80000000
+#define PMU_SLOW_CLK_PERIOD			0x6dc
+
+struct bcm53573_ilp {
+	struct clk_hw hw;
+	struct regmap *regmap;
+};
+
+static int bcm53573_ilp_enable(struct clk_hw *hw)
+{
+	struct bcm53573_ilp *ilp = container_of(hw, struct bcm53573_ilp, hw);
+
+	regmap_write(ilp->regmap, PMU_SLOW_CLK_PERIOD, 0x10199);
+	regmap_write(ilp->regmap, 0x674, 0x10000);
+
+	return 0;
+}
+
+static void bcm53573_ilp_disable(struct clk_hw *hw)
+{
+	struct bcm53573_ilp *ilp = container_of(hw, struct bcm53573_ilp, hw);
+
+	regmap_write(ilp->regmap, PMU_SLOW_CLK_PERIOD, 0);
+	regmap_write(ilp->regmap, 0x674, 0);
+}
+
+static unsigned long bcm53573_ilp_recalc_rate(struct clk_hw *hw,
+					      unsigned long parent_rate)
+{
+	struct bcm53573_ilp *ilp = container_of(hw, struct bcm53573_ilp, hw);
+	struct regmap *regmap = ilp->regmap;
+	u32 last_val, cur_val;
+	int sum = 0, num = 0, loop_num = 0;
+	int avg;
+
+	/* Enable measurement */
+	regmap_write(regmap, PMU_XTAL_FREQ_RATIO, XTAL_CTL_EN);
+
+	/* Read initial value */
+	regmap_read(regmap, PMU_XTAL_FREQ_RATIO, &last_val);
+	last_val &= XTAL_ALP_PER_4ILP;
+
+	/*
+	 * At minimum we should loop for a bit to let hardware do the
+	 * measurement. This isn't very accurate however, so for a better
+	 * precision lets try getting 20 different values for and use average.
+	 */
+	while (num < 20) {
+		regmap_read(regmap, PMU_XTAL_FREQ_RATIO, &cur_val);
+		cur_val &= XTAL_ALP_PER_4ILP;
+
+		if (cur_val != last_val) {
+			/* Got different value, use it */
+			sum += cur_val;
+			num++;
+			loop_num = 0;
+			last_val = cur_val;
+		} else if (++loop_num > 5000) {
+			/* Same value over and over, give up */
+			sum += cur_val;
+			num++;
+			break;
+		}
+
+		cpu_relax();
+	}
+
+	/* Disable measurement to save power */
+	regmap_write(regmap, PMU_XTAL_FREQ_RATIO, 0x0);
+
+	avg = sum / num;
+
+	return parent_rate * 4 / avg;
+}
+
+static const struct clk_ops bcm53573_ilp_clk_ops = {
+	.enable = bcm53573_ilp_enable,
+	.disable = bcm53573_ilp_disable,
+	.recalc_rate = bcm53573_ilp_recalc_rate,
+};
+
+static void bcm53573_ilp_init(struct device_node *np)
+{
+	struct bcm53573_ilp *ilp;
+	struct clk_init_data init = { };
+	const char *parent_name;
+	int err;
+
+	ilp = kzalloc(sizeof(*ilp), GFP_KERNEL);
+	if (!ilp)
+		return;
+
+	parent_name = of_clk_get_parent_name(np, 0);
+	if (!parent_name) {
+		err = -ENOENT;
+		goto err_free_ilp;
+	}
+
+	ilp->regmap = syscon_node_to_regmap(of_get_parent(np));
+	if (IS_ERR(ilp->regmap)) {
+		err = PTR_ERR(ilp->regmap);
+		goto err_free_ilp;
+	}
+
+	init.name = np->name;
+	init.ops = &bcm53573_ilp_clk_ops;
+	init.parent_names = &parent_name;
+	init.num_parents = 1;
+
+	ilp->hw.init = &init;
+	err = clk_hw_register(NULL, &ilp->hw);
+	if (err)
+		goto err_free_ilp;
+
+	err = of_clk_add_hw_provider(np, of_clk_hw_simple_get, &ilp->hw);
+	if (err)
+		goto err_clk_hw_unregister;
+
+	return;
+
+err_clk_hw_unregister:
+	clk_hw_unregister(&ilp->hw);
+err_free_ilp:
+	kfree(ilp);
+	pr_err("Failed to init ILP clock: %d\n", err);
+}
+
+/* We need it very early for arch code, before device model gets ready */
+CLK_OF_DECLARE(bcm53573_ilp_clk, "brcm,bcm53573-ilp", bcm53573_ilp_init);