clk: renesas: cpg-mssr: Add module reset support for RZ/T2H

Add support for module reset handling on the RZ/T2H SoC. Unlike earlier
CPG/MSSR variants, RZ/T2H uses a unified set of Module Reset Control
Registers (MRCR) where both reset and deassert actions are done via
read-modify-write (RMW) to the same register.

Introduce a new MRCR offset table (mrcr_for_rzt2h) for RZ/T2H and assign
it to reset_regs. For this SoC, the number of resets is based on the
number of MRCR registers rather than the number of module clocks. Also
add cpg_mrcr_reset_ops to implement reset, assert, and deassert using RMW
while holding the spinlock. This follows the RZ/T2H requirements, where
processing after releasing a module reset must be secured by performing
seven dummy reads of the same register, and where a module that is reset
and released again must ensure the target bit in the Module Reset Control
Register is set to 1.

Update the reset controller registration to select cpg_mrcr_reset_ops for
RZ/T2H, while keeping the existing cpg_mssr_reset_ops for other SoCs.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://patch.msgid.link/20250929112324.3622148-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Author: prabhakarlad

drivers/clk/renesas/renesas-cpg-mssr.c

@@ -40,6 +40,8 @@
 #define WARN_DEBUG(x)	do { } while (0)
 #endif
 
+#define RZT2H_RESET_REG_READ_COUNT	7
+
 /*
  * Module Standby and Software Reset register offets.
  *
@@ -137,6 +139,22 @@ static const u16 srcr_for_gen4[] = {
 	0x2C60, 0x2C64, 0x2C68, 0x2C6C, 0x2C70, 0x2C74,
 };
 
+static const u16 mrcr_for_rzt2h[] = {
+	0x240,	/* MRCTLA */
+	0x244,	/* Reserved */
+	0x248,	/* Reserved */
+	0x24C,	/* Reserved */
+	0x250,	/* MRCTLE */
+	0x254,	/* Reserved */
+	0x258,	/* Reserved */
+	0x25C,	/* Reserved */
+	0x260,	/* MRCTLI */
+	0x264,	/* Reserved */
+	0x268,	/* Reserved */
+	0x26C,	/* Reserved */
+	0x270,	/* MRCTLM */
+};
+
 /*
  * Software Reset Clearing Register offsets
  */
@@ -739,13 +757,86 @@ static int cpg_mssr_status(struct reset_controller_dev *rcdev,
 	return !!(readl(priv->pub.base0 + priv->reset_regs[reg]) & bitmask);
 }
 
+static int cpg_mrcr_set_reset_state(struct reset_controller_dev *rcdev,
+				    unsigned long id, bool set)
+{
+	struct cpg_mssr_priv *priv = rcdev_to_priv(rcdev);
+	unsigned int reg = id / 32;
+	unsigned int bit = id % 32;
+	u32 bitmask = BIT(bit);
+	void __iomem *reg_addr;
+	unsigned long flags;
+	unsigned int i;
+	u32 val;
+
+	dev_dbg(priv->dev, "%s %u%02u\n", set ? "assert" : "deassert", reg, bit);
+
+	spin_lock_irqsave(&priv->pub.rmw_lock, flags);
+
+	reg_addr = priv->pub.base0 + priv->reset_regs[reg];
+	/* Read current value and modify */
+	val = readl(reg_addr);
+	if (set)
+		val |= bitmask;
+	else
+		val &= ~bitmask;
+	writel(val, reg_addr);
+
+	/*
+	 * For secure processing after release from a module reset, one must
+	 * perform multiple dummy reads of the same register.
+	 */
+	for (i = 0; !set && i < RZT2H_RESET_REG_READ_COUNT; i++)
+		readl(reg_addr);
+
+	/* Verify the operation */
+	val = readl(reg_addr);
+	if (set == !(bitmask & val)) {
+		dev_err(priv->dev, "Reset register %u%02u operation failed\n", reg, bit);
+		spin_unlock_irqrestore(&priv->pub.rmw_lock, flags);
+		return -EIO;
+	}
+
+	spin_unlock_irqrestore(&priv->pub.rmw_lock, flags);
+
+	return 0;
+}
+
+static int cpg_mrcr_reset(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	int ret;
+
+	ret = cpg_mrcr_set_reset_state(rcdev, id, true);
+	if (ret)
+		return ret;
+
+	return cpg_mrcr_set_reset_state(rcdev, id, false);
+}
+
+static int cpg_mrcr_assert(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	return cpg_mrcr_set_reset_state(rcdev, id, true);
+}
+
+static int cpg_mrcr_deassert(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	return cpg_mrcr_set_reset_state(rcdev, id, false);
+}
+
 static const struct reset_control_ops cpg_mssr_reset_ops = {
 	.reset = cpg_mssr_reset,
 	.assert = cpg_mssr_assert,
 	.deassert = cpg_mssr_deassert,
 	.status = cpg_mssr_status,
 };
 
+static const struct reset_control_ops cpg_mrcr_reset_ops = {
+	.reset = cpg_mrcr_reset,
+	.assert = cpg_mrcr_assert,
+	.deassert = cpg_mrcr_deassert,
+	.status = cpg_mssr_status,
+};
+
 static int cpg_mssr_reset_xlate(struct reset_controller_dev *rcdev,
 				const struct of_phandle_args *reset_spec)
 {
@@ -763,11 +854,23 @@ static int cpg_mssr_reset_xlate(struct reset_controller_dev *rcdev,
 
 static int cpg_mssr_reset_controller_register(struct cpg_mssr_priv *priv)
 {
-	priv->rcdev.ops = &cpg_mssr_reset_ops;
+	/*
+	 * RZ/T2H (and family) has the Module Reset Control Registers
+	 * which allows control resets of certain modules.
+	 * The number of resets is not equal to the number of module clocks.
+	 */
+	if (priv->reg_layout == CLK_REG_LAYOUT_RZ_T2H) {
+		priv->rcdev.ops = &cpg_mrcr_reset_ops;
+		priv->rcdev.nr_resets = ARRAY_SIZE(mrcr_for_rzt2h) * 32;
+	} else {
+		priv->rcdev.ops = &cpg_mssr_reset_ops;
+		priv->rcdev.nr_resets = priv->num_mod_clks;
+	}
+
 	priv->rcdev.of_node = priv->dev->of_node;
 	priv->rcdev.of_reset_n_cells = 1;
 	priv->rcdev.of_xlate = cpg_mssr_reset_xlate;
-	priv->rcdev.nr_resets = priv->num_mod_clks;
+
 	return devm_reset_controller_register(priv->dev, &priv->rcdev);
 }
 
@@ -1172,6 +1275,7 @@ static int __init cpg_mssr_common_init(struct device *dev,
 		priv->control_regs = stbcr;
 	} else if (priv->reg_layout == CLK_REG_LAYOUT_RZ_T2H) {
 		priv->control_regs = mstpcr_for_rzt2h;
+		priv->reset_regs = mrcr_for_rzt2h;
 	} else if (priv->reg_layout == CLK_REG_LAYOUT_RCAR_GEN4) {
 		priv->status_regs = mstpsr_for_gen4;
 		priv->control_regs = mstpcr_for_gen4;
@@ -1268,8 +1372,7 @@ static int __init cpg_mssr_probe(struct platform_device *pdev)
 		goto reserve_exit;
 
 	/* Reset Controller not supported for Standby Control SoCs */
-	if (priv->reg_layout == CLK_REG_LAYOUT_RZ_A ||
-	    priv->reg_layout == CLK_REG_LAYOUT_RZ_T2H)
+	if (priv->reg_layout == CLK_REG_LAYOUT_RZ_A)
 		goto reserve_exit;
 
 	error = cpg_mssr_reset_controller_register(priv);