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

[Andy Shevchenko <andy@kernel.org>]

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.

-- 
With Best Regards,
Andy Shevchenko