clk: renesas: vbattb: Add VBATTB clock driver

The VBATTB IP of the Renesas RZ/G3S SoC controls the clock that is used
by the RTC. The input to the VBATTB could be a 32KHz crystal
or an external clock device.

The HW block diagram for the clock generator is as follows:

           +----------+ XC   `\
RTXIN  --->|          |----->| \       +----+  VBATTCLK
           | 32K clock|      |  |----->|gate|----------->
           | osc      | XBYP |  |      +----+
RTXOUT --->|          |----->| /
           +----------+      ,

After discussions w/ Stephen Boyd the clock tree associated with this
hardware block was exported in Linux as:

vbattb-xtal
   xbyp
   xc
      mux
         vbattbclk

where:
- input-xtal is the input clock (connected to RTXIN, RTXOUT pins)
- xc, xbyp are mux inputs
- mux is the internal mux
- vbattclk is the gate clock that feeds in the end the RTC

to allow selecting the input of the MUX though assigned-clock DT
properties, using the already existing clock drivers and avoid adding
other DT properties. If the crystal is connected on RTXIN,
RTXOUT pins the XC will be selected as mux input. If an external clock
device is connected on RTXIN, RTXOUT pins the XBYP will be selected as
mux input.

The load capacitance of the internal crystal can be configured
with renesas,vbattb-load-nanofarads DT property.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Link: https://lore.kernel.org/20241101095720.2247815-4-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

drivers/clk/renesas/Kconfig

@@ -237,6 +237,11 @@ config CLK_RZV2H
 	bool "RZ/V2H(P) family clock support" if COMPILE_TEST
 	select RESET_CONTROLLER
 
+config CLK_RENESAS_VBATTB
+	tristate "Renesas VBATTB clock controller"
+	depends on ARCH_RZG2L || COMPILE_TEST
+	select RESET_CONTROLLER
+
 # Generic
 config CLK_RENESAS_CPG_MSSR
 	bool "CPG/MSSR clock support" if COMPILE_TEST

drivers/clk/renesas/Makefile

@@ -53,3 +53,4 @@ obj-$(CONFIG_CLK_RZV2H)			+= rzv2h-cpg.o
 obj-$(CONFIG_CLK_RENESAS_CPG_MSSR)	+= renesas-cpg-mssr.o
 obj-$(CONFIG_CLK_RENESAS_CPG_MSTP)	+= clk-mstp.o
 obj-$(CONFIG_CLK_RENESAS_DIV6)		+= clk-div6.o
+obj-$(CONFIG_CLK_RENESAS_VBATTB)	+= clk-vbattb.o

drivers/clk/renesas/clk-vbattb.c

@@ -0,0 +1,205 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * VBATTB clock driver
+ *
+ * Copyright (C) 2024 Renesas Electronics Corp.
+ */
+
+#include <linux/cleanup.h>
+#include <linux/clk-provider.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/mod_devicetable.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pm_runtime.h>
+#include <linux/reset.h>
+
+#include <dt-bindings/clock/renesas,r9a08g045-vbattb.h>
+
+#define VBATTB_BKSCCR			0x1c
+#define VBATTB_BKSCCR_SOSEL		6
+#define VBATTB_SOSCCR2			0x24
+#define VBATTB_SOSCCR2_SOSTP2		0
+#define VBATTB_XOSCCR			0x30
+#define VBATTB_XOSCCR_OUTEN		16
+#define VBATTB_XOSCCR_XSEL		GENMASK(1, 0)
+#define VBATTB_XOSCCR_XSEL_4_PF		0x0
+#define VBATTB_XOSCCR_XSEL_7_PF		0x1
+#define VBATTB_XOSCCR_XSEL_9_PF		0x2
+#define VBATTB_XOSCCR_XSEL_12_5_PF	0x3
+
+/**
+ * struct vbattb_clk - VBATTB clock data structure
+ * @base: base address
+ * @lock: lock
+ */
+struct vbattb_clk {
+	void __iomem *base;
+	spinlock_t lock;
+};
+
+static int vbattb_clk_validate_load_capacitance(u32 *reg_lc, u32 of_lc)
+{
+	switch (of_lc) {
+	case 4000:
+		*reg_lc = VBATTB_XOSCCR_XSEL_4_PF;
+		break;
+	case 7000:
+		*reg_lc = VBATTB_XOSCCR_XSEL_7_PF;
+		break;
+	case 9000:
+		*reg_lc = VBATTB_XOSCCR_XSEL_9_PF;
+		break;
+	case 12500:
+		*reg_lc = VBATTB_XOSCCR_XSEL_12_5_PF;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void vbattb_clk_action(void *data)
+{
+	struct device *dev = data;
+	struct reset_control *rstc = dev_get_drvdata(dev);
+	int ret;
+
+	ret = reset_control_assert(rstc);
+	if (ret)
+		dev_err(dev, "Failed to de-assert reset!");
+
+	ret = pm_runtime_put_sync(dev);
+	if (ret < 0)
+		dev_err(dev, "Failed to runtime suspend!");
+
+	of_clk_del_provider(dev->of_node);
+}
+
+static int vbattb_clk_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct clk_parent_data parent_data = {};
+	struct clk_hw_onecell_data *clk_data;
+	const struct clk_hw *parent_hws[2];
+	struct device *dev = &pdev->dev;
+	struct reset_control *rstc;
+	struct vbattb_clk *vbclk;
+	u32 of_lc, reg_lc;
+	struct clk_hw *hw;
+	/* 4 clocks are exported: VBATTB_XC, VBATTB_XBYP, VBATTB_MUX, VBATTB_VBATTCLK. */
+	u8 num_clks = 4;
+	int ret;
+
+	/* Default to 4pF as this is not needed if external clock device is connected. */
+	of_lc = 4000;
+	of_property_read_u32(np, "quartz-load-femtofarads", &of_lc);
+
+	ret = vbattb_clk_validate_load_capacitance(&reg_lc, of_lc);
+	if (ret)
+		return ret;
+
+	vbclk = devm_kzalloc(dev, sizeof(*vbclk), GFP_KERNEL);
+	if (!vbclk)
+		return -ENOMEM;
+
+	clk_data = devm_kzalloc(dev, struct_size(clk_data, hws, num_clks), GFP_KERNEL);
+	if (!clk_data)
+		return -ENOMEM;
+	clk_data->num = num_clks;
+
+	vbclk->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(vbclk->base))
+		return PTR_ERR(vbclk->base);
+
+	ret = devm_pm_runtime_enable(dev);
+	if (ret)
+		return ret;
+
+	rstc = devm_reset_control_get_shared(dev, NULL);
+	if (IS_ERR(rstc))
+		return PTR_ERR(rstc);
+
+	ret = pm_runtime_resume_and_get(dev);
+	if (ret)
+		return ret;
+
+	ret = reset_control_deassert(rstc);
+	if (ret) {
+		pm_runtime_put_sync(dev);
+		return ret;
+	}
+
+	dev_set_drvdata(dev, rstc);
+	ret = devm_add_action_or_reset(dev, vbattb_clk_action, dev);
+	if (ret)
+		return ret;
+
+	spin_lock_init(&vbclk->lock);
+
+	parent_data.fw_name = "rtx";
+	hw = devm_clk_hw_register_gate_parent_data(dev, "xc", &parent_data, 0,
+						   vbclk->base + VBATTB_SOSCCR2,
+						   VBATTB_SOSCCR2_SOSTP2,
+						   CLK_GATE_SET_TO_DISABLE, &vbclk->lock);
+	if (IS_ERR(hw))
+		return PTR_ERR(hw);
+	clk_data->hws[VBATTB_XC] = hw;
+
+	hw = devm_clk_hw_register_fixed_factor_fwname(dev, np, "xbyp", "rtx", 0, 1, 1);
+	if (IS_ERR(hw))
+		return PTR_ERR(hw);
+	clk_data->hws[VBATTB_XBYP] = hw;
+
+	parent_hws[0] = clk_data->hws[VBATTB_XC];
+	parent_hws[1] = clk_data->hws[VBATTB_XBYP];
+	hw = devm_clk_hw_register_mux_parent_hws(dev, "mux", parent_hws, 2, 0,
+						 vbclk->base + VBATTB_BKSCCR,
+						 VBATTB_BKSCCR_SOSEL,
+						 1, 0, &vbclk->lock);
+	if (IS_ERR(hw))
+		return PTR_ERR(hw);
+	clk_data->hws[VBATTB_MUX] = hw;
+
+	/* Set load capacitance before registering the VBATTCLK clock. */
+	scoped_guard(spinlock, &vbclk->lock) {
+		u32 val = readl_relaxed(vbclk->base + VBATTB_XOSCCR);
+
+		val &= ~VBATTB_XOSCCR_XSEL;
+		val |= reg_lc;
+		writel_relaxed(val, vbclk->base + VBATTB_XOSCCR);
+	}
+
+	/* This feeds the RTC counter clock and it needs to stay on. */
+	hw = devm_clk_hw_register_gate_parent_hw(dev, "vbattclk", hw, CLK_IS_CRITICAL,
+						 vbclk->base + VBATTB_XOSCCR,
+						 VBATTB_XOSCCR_OUTEN, 0,
+						 &vbclk->lock);
+
+	if (IS_ERR(hw))
+		return PTR_ERR(hw);
+	clk_data->hws[VBATTB_VBATTCLK] = hw;
+
+	return of_clk_add_hw_provider(np, of_clk_hw_onecell_get, clk_data);
+}
+
+static const struct of_device_id vbattb_clk_match[] = {
+	{ .compatible = "renesas,r9a08g045-vbattb" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, vbattb_clk_match);
+
+static struct platform_driver vbattb_clk_driver = {
+	.driver		= {
+		.name	= "renesas-vbattb-clk",
+		.of_match_table = vbattb_clk_match,
+	},
+	.probe = vbattb_clk_probe,
+};
+module_platform_driver(vbattb_clk_driver);
+
+MODULE_DESCRIPTION("Renesas VBATTB Clock Driver");
+MODULE_AUTHOR("Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>");
+MODULE_LICENSE("GPL");