According to the chip manual, the I2C register access type of Loongson-2K2000/LS7A is "B", so we can only access registers in byte form (readb()/writeb()).

Although Loongson-2K0500/Loongson-2K1000 do not have similar constraints, register accesses in byte form also behave correctly.

Also, in hardware, the frequency division registers are defined as two separate registers (high 8-bit and low 8-bit), so we just access them directly as bytes.

Cc: stable@vger.kernel.org Fixes: 015e61f0bffd ("i2c: ls2x: Add driver for Loongson-2K/LS7A I2C controller") Co-developed-by: Hongliang Wang wanghongliang@loongson.cn Signed-off-by: Hongliang Wang wanghongliang@loongson.cn Signed-off-by: Binbin Zhou zhoubinbin@loongson.cn Reviewed-by: Andy Shevchenko andy@kernel.org --- V3: - Add Reviewed-by tag from Andy, thanks; - In comment and commit message, readb->read()/writeb->writeb().

Link to V2: https://lore.kernel.org/all/20250219020809.3568972-1-zhoubinbin@loongson.cn/

V2: - Add a comment to prevent from changing that back to 16-bit write.

Link to V1: https://lore.kernel.org/all/20250218111133.3058590-1-zhoubinbin@loongson.cn/

drivers/i2c/busses/i2c-ls2x.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-ls2x.c b/drivers/i2c/busses/i2c-ls2x.c index 8821cac3897b..b475dd27b7af 100644 --- a/drivers/i2c/busses/i2c-ls2x.c +++ b/drivers/i2c/busses/i2c-ls2x.c @@ -10,6 +10,7 @@ * Rewritten for mainline by Binbin Zhou zhoubinbin@loongson.cn */

+#include <linux/bitfield.h> #include <linux/bits.h> #include <linux/completion.h> #include <linux/device.h> @@ -26,7 +27,8 @@ #include <linux/units.h>

/* I2C Registers */ -#define I2C_LS2X_PRER 0x0 /* Freq Division Register(16 bits) */ +#define I2C_LS2X_PRER_LO 0x0 /* Freq Division Low Byte Register */ +#define I2C_LS2X_PRER_HI 0x1 /* Freq Division High Byte Register */ #define I2C_LS2X_CTR 0x2 /* Control Register */ #define I2C_LS2X_TXR 0x3 /* Transport Data Register */ #define I2C_LS2X_RXR 0x3 /* Receive Data Register */ @@ -93,6 +95,7 @@ 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; struct i2c_timings *t = &priv->i2c_t; struct device *dev = priv->adapter.dev.parent; u32 acpi_speed = i2c_acpi_find_bus_speed(dev); @@ -104,9 +107,14 @@ static void ls2x_i2c_adjust_bus_speed(struct ls2x_i2c_priv *priv) else t->bus_freq_hz = LS2X_I2C_FREQ_STD;

- /* Calculate and set i2c frequency. */ - writew(LS2X_I2C_PCLK_FREQ / (5 * t->bus_freq_hz) - 1, - priv->base + I2C_LS2X_PRER); + /* + * 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); }

static void ls2x_i2c_init(struct ls2x_i2c_priv *priv)

base-commit: 7e45b505e699f4c80aa8bf79b4ea2a5f5a66bb51