Re: [PATCH] i2c: ls2x: Fix frequency division register access

On Tue, Feb 18, 2025 at 07:11:33PM +0800, Binbin Zhou wrote:

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.

...

/* Calculate and set i2c frequency. */

• writew(LS2X_I2C_PCLK_FREQ / (5 * t->bus_freq_hz) - 1,

•       priv->base + I2C_LS2X_PRER);
  

• 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);

Now this needs a comment to prevent from appearing a patch that basically changes that back to 16-bit write.