clk: keystone: Add new driver to handle syscon based clocks

On TI's AM654/J721e SoCs, certain clocks can be gated/ungated by setting
a single bit in SoC's System Control Module registers. Sometime more
than one clock control can be in the same register.

Add a driver to support such clocks using syscon framework. Driver
currently supports controlling EHRPWM's TimeBase clock(TBCLK) for AM654
SoC.

Signed-off-by: Vignesh Raghavendra <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

drivers/clk/keystone/Kconfig

···
 	  This is mostly only useful for debugging purposes, and will
 	  increase the boot time of the device. If you want the clocks probed
 	  from firmware, say Y. Otherwise, say N.
+
+config TI_SYSCON_CLK
+	tristate "Syscon based clock driver for K2/K3 SoCs"
+	depends on ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
+	default ARCH_KEYSTONE || ARCH_K3
+	help
+	  This adds clock driver support for syscon based gate
+	  clocks on TI's K2 and K3 SoCs.

drivers/clk/keystone/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_COMMON_CLK_KEYSTONE)	+= pll.o gate.o
 obj-$(CONFIG_TI_SCI_CLK)		+= sci-clk.o
+obj-$(CONFIG_TI_SYSCON_CLK)		+= syscon-clk.o

drivers/clk/keystone/syscon-clk.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Texas Instruments Incorporated - http://www.ti.com/
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+struct ti_syscon_gate_clk_priv {
+	struct clk_hw hw;
+	struct regmap *regmap;
+	u32 reg;
+	u32 idx;
+};
+
+struct ti_syscon_gate_clk_data {
+	char *name;
+	u32 offset;
+	u32 bit_idx;
+};
+
+static struct
+ti_syscon_gate_clk_priv *to_ti_syscon_gate_clk_priv(struct clk_hw *hw)
+{
+	return container_of(hw, struct ti_syscon_gate_clk_priv, hw);
+}
+
+static int ti_syscon_gate_clk_enable(struct clk_hw *hw)
+{
+	struct ti_syscon_gate_clk_priv *priv = to_ti_syscon_gate_clk_priv(hw);
+
+	return regmap_write_bits(priv->regmap, priv->reg, priv->idx,
+				 priv->idx);
+}
+
+static void ti_syscon_gate_clk_disable(struct clk_hw *hw)
+{
+	struct ti_syscon_gate_clk_priv *priv = to_ti_syscon_gate_clk_priv(hw);
+
+	regmap_write_bits(priv->regmap, priv->reg, priv->idx, 0);
+}
+
+static int ti_syscon_gate_clk_is_enabled(struct clk_hw *hw)
+{
+	unsigned int val;
+	struct ti_syscon_gate_clk_priv *priv = to_ti_syscon_gate_clk_priv(hw);
+
+	regmap_read(priv->regmap, priv->reg, &val);
+
+	return !!(val & priv->idx);
+}
+
+static const struct clk_ops ti_syscon_gate_clk_ops = {
+	.enable		= ti_syscon_gate_clk_enable,
+	.disable	= ti_syscon_gate_clk_disable,
+	.is_enabled	= ti_syscon_gate_clk_is_enabled,
+};
+
+static struct clk_hw
+*ti_syscon_gate_clk_register(struct device *dev, struct regmap *regmap,
+			     const struct ti_syscon_gate_clk_data *data)
+{
+	struct ti_syscon_gate_clk_priv *priv;
+	struct clk_init_data init;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return ERR_PTR(-ENOMEM);
+
+	init.name = data->name;
+	init.ops = &ti_syscon_gate_clk_ops;
+	init.parent_names = NULL;
+	init.num_parents = 0;
+	init.flags = 0;
+
+	priv->regmap = regmap;
+	priv->reg = data->offset;
+	priv->idx = BIT(data->bit_idx);
+	priv->hw.init = &init;
+
+	ret = devm_clk_hw_register(dev, &priv->hw);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return &priv->hw;
+}
+
+static int ti_syscon_gate_clk_probe(struct platform_device *pdev)
+{
+	const struct ti_syscon_gate_clk_data *data, *p;
+	struct clk_hw_onecell_data *hw_data;
+	struct device *dev = &pdev->dev;
+	struct regmap *regmap;
+	int num_clks, i;
+
+	data = device_get_match_data(dev);
+	if (!data)
+		return -EINVAL;
+
+	regmap = syscon_node_to_regmap(dev->of_node);
+	if (IS_ERR(regmap)) {
+		if (PTR_ERR(regmap) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
+		dev_err(dev, "failed to find parent regmap\n");
+		return PTR_ERR(regmap);
+	}
+
+	num_clks = 0;
+	for (p = data; p->name; p++)
+		num_clks++;
+
+	hw_data = devm_kzalloc(dev, struct_size(hw_data, hws, num_clks),
+			       GFP_KERNEL);
+	if (!hw_data)
+		return -ENOMEM;
+
+	hw_data->num = num_clks;
+
+	for (i = 0; i < num_clks; i++) {
+		hw_data->hws[i] = ti_syscon_gate_clk_register(dev, regmap,
+							      &data[i]);
+		if (IS_ERR(hw_data->hws[i]))
+			dev_warn(dev, "failed to register %s\n",
+				 data[i].name);
+	}
+
+	return devm_of_clk_add_hw_provider(dev, of_clk_hw_onecell_get,
+					   hw_data);
+}
+
+#define TI_SYSCON_CLK_GATE(_name, _offset, _bit_idx)	\
+	{						\
+		.name = _name,				\
+		.offset = (_offset),			\
+		.bit_idx = (_bit_idx),			\
+	}
+
+static const struct ti_syscon_gate_clk_data am654_clk_data[] = {
+	TI_SYSCON_CLK_GATE("ehrpwm_tbclk0", 0x0, 0),
+	TI_SYSCON_CLK_GATE("ehrpwm_tbclk1", 0x4, 0),
+	TI_SYSCON_CLK_GATE("ehrpwm_tbclk2", 0x8, 0),
+	TI_SYSCON_CLK_GATE("ehrpwm_tbclk3", 0xc, 0),
+	TI_SYSCON_CLK_GATE("ehrpwm_tbclk4", 0x10, 0),
+	TI_SYSCON_CLK_GATE("ehrpwm_tbclk5", 0x14, 0),
+	{ /* Sentinel */ },
+};
+
+static const struct of_device_id ti_syscon_gate_clk_ids[] = {
+	{
+		.compatible = "ti,am654-ehrpwm-tbclk",
+		.data = &am654_clk_data,
+	},
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ti_syscon_gate_clk_ids);
+
+static struct platform_driver ti_syscon_gate_clk_driver = {
+	.probe = ti_syscon_gate_clk_probe,
+	.driver = {
+		.name = "ti-syscon-gate-clk",
+		.of_match_table = ti_syscon_gate_clk_ids,
+	},
+};
+module_platform_driver(ti_syscon_gate_clk_driver);
+
+MODULE_AUTHOR("Vignesh Raghavendra <[e-mail]>");
+MODULE_DESCRIPTION("Syscon backed gate-clock driver");
+MODULE_LICENSE("GPL");