Re: [PATCH v4 3/3] drm/xe/i2c: Keep the i2c controller always enabled

[Raag Jadav]

On Mon, Jul 13, 2026 at 05:56:01PM +0200, Heikki Krogerus wrote:
> Some platforms make an assumption that the i2c controller's
> enabled state indicates also the power state of the
> controller. This can create a problem when the controller is
> in disabled state, because the hardware may assume
> incorrectly that it is then also in low-power state.
> 
> To fix this, the controller is kept enabled by taking over
> the IC_ENABLE register. The controller has to be disabled
> when the configuration is updated and when the target
> address or the slave address are assigned, so disabling it
> when IC_CON, IC_TAR or IC_SAR registers are programmed, and
> then re-enabling it again.

...

> +/* See "Disabling DW_apb_i2c" in the DesignWare DW_abp_i2c databook. */
> +static void xe_i2c_disable(struct xe_i2c *i2c)
> +{
> +	int timeout = 100;
> +	u32 status;
> +
> +	xe_mmio_rmw32(i2c->mmio, I2C_REG(DW_IC_ENABLE), 1, 0);

Can we use DW_IC_ENABLE_* defines?

> +	do {
> +		status = xe_mmio_read32(i2c->mmio, I2C_REG(DW_IC_ENABLE_STATUS));
> +		if (!(status & 1))

Ditto for DW_IC_STATUS_*.

> +			return;
> +		/* Can't sleep here. */
> +		udelay(25);
> +	} while (timeout--);
> +
> +	dev_warn(&i2c->adapter->dev, "timeout in disabling adapter\n");
> +}

...

> @@ -230,7 +260,28 @@ static int xe_i2c_write(void *context, unsigned int reg, unsigned int val)
>  {
>  	struct xe_i2c *i2c = context;
>  
> -	xe_mmio_write32(i2c->mmio, XE_REG(reg + I2C_MEM_SPACE_OFFSET), val);
> +	switch (reg) {
> +	case DW_IC_CON:
> +	case DW_IC_TAR:
> +	case DW_IC_SAR:
> +		/* Disable the controller. */
> +		xe_i2c_disable(i2c);
> +
> +		/* Write the register. */
> +		xe_mmio_write32(i2c->mmio, I2C_REG(reg), val);
> +
> +		/* Enable the controller. */
> +		xe_mmio_rmw32(i2c->mmio, I2C_REG(DW_IC_ENABLE), 0, 1);

Ditto.

Raag

> +		break;
> +	case DW_IC_ENABLE:
> +		i2c->ic_enable = val;
> +		/* Other fields can be updated except the enable bit. */
> +		val |= DW_IC_ENABLE_ENABLE;
> +		fallthrough;
> +	default:
> +		xe_mmio_write32(i2c->mmio, I2C_REG(reg), val);
> +		break;
> +	}
>  
>  	return 0;
>  }