[PATCH v9 2/2] i2c: ls2x: Add clocks property parsing and adjust bus speed

[Hongliang Wang <wanghongliang@loongson.cn>]

The original driver uses a fixed PCLK frequency(LS2X_I2C_PCLK_FREQ) and
fixed div(5) for I2C bus speed calculation. As PCLK frequency and div
vary on different SoCs and ACPI platforms, this leads to inaccurate I2C
bus speed calculation and poor adaptability across platforms.

Improve the accuracy of I2C bus speed calculation across different
platforms by parsing the real I2C bus reference clock (PCLK) and div.
Support both DTS and ACPI.

For DTS:
- Retrieve I2C bus reference clock via the common clock framework
- Fetch div from match data for LS2K/LS7A series
- Fallback to default values if clock lookup fails or the obtained
  pclk or div is zero

For ACPI:
- Parse "clocks" property to get I2C bus reference clock
- Parse "clock-div" property to get div
- Fallback to the default values if property parsing fails or the
  obtained pclk or div is zero

Calculate the I2C clock prescaler based on reference clock, div and
target bus frequency with the formula:

prescale = (pclk * 10) / (div * bus_freq_hz) - 1

Dynamically acquiring PCLK and div per platform ensures accurate I2C bus
speed calculation and reliable operation across different platforms.

Tested-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Cc: stable@vger.kernel.org
Signed-off-by: Hongliang Wang <wanghongliang@loongson.cn>
---
 drivers/i2c/busses/i2c-ls2x.c | 43 ++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-ls2x.c b/drivers/i2c/busses/i2c-ls2x.c
index b475dd27b7af..65451fc9145b 100644
--- a/drivers/i2c/busses/i2c-ls2x.c
+++ b/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 +64,19 @@
 /* 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;
+	unsigned int		pclk;
 };
 
 /*
@@ -107,12 +116,13 @@ static void ls2x_i2c_adjust_bus_speed(struct ls2x_i2c_priv *priv)
 	else
 		t->bus_freq_hz = LS2X_I2C_FREQ_STD;
 
+	val = ((u64)priv->pclk * 10) / ((u64)priv->div * 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);
 }
@@ -287,6 +297,7 @@ static const struct i2c_algorithm ls2x_i2c_algo = {
 static int ls2x_i2c_probe(struct platform_device *pdev)
 {
 	int ret, irq;
+	struct clk *clk;
 	struct i2c_adapter *adap;
 	struct ls2x_i2c_priv *priv;
 	struct device *dev = &pdev->dev;
@@ -304,6 +315,32 @@ static int ls2x_i2c_probe(struct platform_device *pdev)
 	if (irq < 0)
 		return irq;
 
+	if (dev_of_node(dev)) {
+		clk = devm_clk_get_optional_enabled(dev, NULL);
+		if (IS_ERR(clk))
+			return PTR_ERR(clk);
+		if (clk) {
+			priv->pclk = clk_get_rate(clk);
+			if (!priv->pclk)
+				priv->pclk = LS2X_I2C_PCLK_FREQ;
+		} else {
+			priv->pclk = LS2X_I2C_PCLK_FREQ;
+		}
+
+		priv->div = (unsigned long)device_get_match_data(dev);
+		if (!priv->div)
+			priv->div = LS2X_I2C_2K_CLOCK_DIV;
+	} else {
+		/* clocks and clock-div properties are used only in ACPI path. */
+		ret = device_property_read_u32(dev, "clocks", &priv->pclk);
+		if (ret || !priv->pclk)
+			priv->pclk = LS2X_I2C_PCLK_FREQ;
+
+		ret = device_property_read_u32(dev, "clock-div", &priv->div);
+		if (ret || !priv->div)
+			priv->div = LS2X_I2C_7A_CLOCK_DIV;
+	}
+
 	/* Add the i2c adapter */
 	adap = &priv->adapter;
 	adap->retries = 5;
@@ -349,8 +386,8 @@ 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);
-- 
2.47.2