FROMLIST: i2c: ls2x: Add clocks property parsing and adjust bus speed

The i2c-ls2x driver supports dts and acpi parameter passing.

In dts, uses clock framework, by parsing clocks property to
get i2c bus reference clock, and define the div of reference
clock by device data.

In acpi, by passing clocks property to describe i2c bus reference
clock and clock-div property to describe the div of reference clock.

Based on i2c bus reference clock(clock_a), i2c bus speed(clock_s)
and div, calculate the prcescale of i2c divider register. The
calculation formula is

prcescale = (clock_a*10)/(div*clock_s)-1

Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Cc: stable@vger.kernel.org
Signed-off-by: Hongliang Wang <wanghongliang@loongson.cn>

Link: https://lore.kernel.org/loongarch/20260608024533.32419-1-wanghongliang@loongson.cn/
Signed-off-by: Mingcong Bai <jeffbai@aosc.io>

Author: wang-whl

drivers/i2c/busses/i2c-ls2x.c

@@ -12,6 +12,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/bits.h>
+#include <linux/clk.h>
 #include <linux/completion.h>
 #include <linux/device.h>
 #include <linux/iopoll.h>
@@ -63,11 +64,18 @@
 /* The default bus frequency, which is an empirical value */
 #define LS2X_I2C_FREQ_STD	(33 * HZ_PER_KHZ)
 
+/* The div of i2c reference clock on LS2K0500/2K1000/2K2000 */
+#define LS2X_I2C_2K_CLOCK_DIV	40
+
+/* The div of i2c reference clock on LS7A1000/7A2000 */
+#define LS2X_I2C_7A_CLOCK_DIV	50
+
 struct ls2x_i2c_priv {
 	struct i2c_adapter	adapter;
 	void __iomem		*base;
 	struct i2c_timings	i2c_t;
 	struct completion	cmd_complete;
+	unsigned int		div;
 };
 
 /*
@@ -96,6 +104,8 @@ static irqreturn_t ls2x_i2c_isr(int this_irq, void *dev_id)
 static void ls2x_i2c_adjust_bus_speed(struct ls2x_i2c_priv *priv)
 {
 	u16 val;
+	u32 pclk, div;
+	struct clk *clk;
 	struct i2c_timings *t = &priv->i2c_t;
 	struct device *dev = priv->adapter.dev.parent;
 	u32 acpi_speed = i2c_acpi_find_bus_speed(dev);
@@ -107,12 +117,30 @@ static void ls2x_i2c_adjust_bus_speed(struct ls2x_i2c_priv *priv)
 	else
 		t->bus_freq_hz = LS2X_I2C_FREQ_STD;
 
+	if (dev_of_node(dev)) {
+		clk = devm_clk_get_optional_enabled(dev, NULL);
+		if (!IS_ERR_OR_NULL(clk))
+			pclk = clk_get_rate(clk);
+		else
+			pclk = LS2X_I2C_PCLK_FREQ;
+
+		div = priv->div;
+
+		val = (pclk * 10) / (div * t->bus_freq_hz) - 1;
+	} else {
+		/* clocks and clock-div are only ACPI properties. */
+		if (!device_property_read_u32(dev, "clocks", &pclk) &&
+		    !device_property_read_u32(dev, "clock-div", &div))
+			val = (pclk * 10) / (div * t->bus_freq_hz) - 1;
+		else
+			val = LS2X_I2C_PCLK_FREQ / (5 * t->bus_freq_hz) - 1;
+	}
+
 	/*
 	 * According to the chip manual, we can only access the registers as bytes,
 	 * otherwise the high bits will be truncated.
 	 * So set the I2C frequency with a sequential writeb() instead of writew().
 	 */
-	val = LS2X_I2C_PCLK_FREQ / (5 * t->bus_freq_hz) - 1;
 	writeb(FIELD_GET(GENMASK(7, 0), val), priv->base + I2C_LS2X_PRER_LO);
 	writeb(FIELD_GET(GENMASK(15, 8), val), priv->base + I2C_LS2X_PRER_HI);
 }
@@ -295,6 +323,8 @@ static int ls2x_i2c_probe(struct platform_device *pdev)
 	if (!priv)
 		return -ENOMEM;
 
+	priv->div = (unsigned long)device_get_match_data(dev);
+
 	/* Map hardware registers */
 	priv->base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(priv->base))
@@ -349,8 +379,8 @@ static DEFINE_RUNTIME_DEV_PM_OPS(ls2x_i2c_pm_ops,
 				 ls2x_i2c_suspend, ls2x_i2c_resume, NULL);
 
 static const struct of_device_id ls2x_i2c_id_table[] = {
-	{ .compatible = "loongson,ls2k-i2c" },
-	{ .compatible = "loongson,ls7a-i2c" },
+	{ .compatible = "loongson,ls2k-i2c", .data = (void *)LS2X_I2C_2K_CLOCK_DIV, },
+	{ .compatible = "loongson,ls7a-i2c", .data = (void *)LS2X_I2C_7A_CLOCK_DIV, },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, ls2x_i2c_id_table);