clk: ti: add gate clock driver

The patch adds support for TI gate clock binding. The code is based on
the drivers/clk/ti/gate.c driver of the Linux kernel version 5.9-rc7.
For DT binding details see:
- Documentation/devicetree/bindings/clock/ti/gate.txt

Signed-off-by: Dario Binacchi <dariobin@libero.it>

drivers/clk/ti/Kconfig

@@ -16,6 +16,12 @@ config CLK_TI_DIVIDER
 	help
 	  This enables the divider clock driver support on TI's SoCs.
 
+config CLK_TI_GATE
+	bool "TI gate clock driver"
+	depends on CLK && OF_CONTROL
+	help
+	  This enables the gate clock driver support on TI's SoCs.
+
 config CLK_TI_MUX
 	bool "TI mux clock driver"
 	depends on CLK && OF_CONTROL && CLK_CCF

drivers/clk/ti/Makefile

@@ -7,4 +7,5 @@ obj-$(CONFIG_ARCH_OMAP2PLUS) += clk.o
 
 obj-$(CONFIG_CLK_TI_AM3_DPLL) += clk-am3-dpll.o clk-am3-dpll-x2.o
 obj-$(CONFIG_CLK_TI_DIVIDER) += clk-divider.o
+obj-$(CONFIG_CLK_TI_GATE) += clk-gate.o
 obj-$(CONFIG_CLK_TI_MUX) += clk-mux.o

drivers/clk/ti/clk-gate.c

@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * TI gate clock support
+ *
+ * Copyright (C) 2020 Dario Binacchi <dariobin@libero.it>
+ *
+ * Loosely based on Linux kernel drivers/clk/ti/gate.c
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <dm/device_compat.h>
+#include <clk-uclass.h>
+#include <asm/io.h>
+#include <linux/clk-provider.h>
+
+struct clk_ti_gate_priv {
+	fdt_addr_t reg;
+	u8 enable_bit;
+	u32 flags;
+	bool invert_enable;
+};
+
+static int clk_ti_gate_disable(struct clk *clk)
+{
+	struct clk_ti_gate_priv *priv = dev_get_priv(clk->dev);
+	u32 v;
+
+	v = readl(priv->reg);
+	if (priv->invert_enable)
+		v |= (1 << priv->enable_bit);
+	else
+		v &= ~(1 << priv->enable_bit);
+
+	writel(v, priv->reg);
+	/* No OCP barrier needed here since it is a disable operation */
+	return 0;
+}
+
+static int clk_ti_gate_enable(struct clk *clk)
+{
+	struct clk_ti_gate_priv *priv = dev_get_priv(clk->dev);
+	u32 v;
+
+	v = readl(priv->reg);
+	if (priv->invert_enable)
+		v &= ~(1 << priv->enable_bit);
+	else
+		v |= (1 << priv->enable_bit);
+
+	writel(v, priv->reg);
+	/* OCP barrier */
+	v = readl(priv->reg);
+	return 0;
+}
+
+static int clk_ti_gate_of_to_plat(struct udevice *dev)
+{
+	struct clk_ti_gate_priv *priv = dev_get_priv(dev);
+
+	priv->reg = dev_read_addr(dev);
+	if (priv->reg == FDT_ADDR_T_NONE) {
+		dev_err(dev, "failed to get control register\n");
+		return -EINVAL;
+	}
+
+	dev_dbg(dev, "reg=0x%08lx\n", priv->reg);
+	priv->enable_bit = dev_read_u32_default(dev, "ti,bit-shift", 0);
+	if (dev_read_bool(dev, "ti,set-rate-parent"))
+		priv->flags |= CLK_SET_RATE_PARENT;
+
+	priv->invert_enable = dev_read_bool(dev, "ti,set-bit-to-disable");
+	return 0;
+}
+
+static struct clk_ops clk_ti_gate_ops = {
+	.enable = clk_ti_gate_enable,
+	.disable = clk_ti_gate_disable,
+};
+
+static const struct udevice_id clk_ti_gate_of_match[] = {
+	{ .compatible = "ti,gate-clock" },
+	{ },
+};
+
+U_BOOT_DRIVER(clk_ti_gate) = {
+	.name = "ti_gate_clock",
+	.id = UCLASS_CLK,
+	.of_match = clk_ti_gate_of_match,
+	.ofdata_to_platdata = clk_ti_gate_of_to_plat,
+	.priv_auto = sizeof(struct clk_ti_gate_priv),
+	.ops = &clk_ti_gate_ops,
+};