Re: [PATCH v9] i2c: designware: fix controller is holding SCL low while ENABLE bit is disabled

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Sep 11, 2024 at 04:39:45PM +0800, Kimriver Liu wrote:
> It was observed that issuing ABORT bit (IC_ENABLE[1]) will not
> work when IC_ENABLE is already disabled.
> 
> Check if ENABLE bit (IC_ENABLE[0]) is disabled when the controller
> is holding SCL low. If ENABLE bit is disabled, the software need
> to enable it before trying to issue ABORT bit. otherwise,
> the controller ignores any write to ABORT bit.
> 
> These kernel logs show up whenever an I2C transaction is
> attempted after this failure.
> i2c_designware e95e0000.i2c: timeout waiting for bus ready
> i2c_designware e95e0000.i2c: timeout in disabling adapter
> 
> The patch can be fix the controller cannot be disabled while
> SCL is held low in ENABLE bit is already disabled.

...

> +/*
> + * This functions waits controller idling before disabling I2C
> + * When the controller is not in the IDLE state,
> + * MST_ACTIVITY bit (IC_STATUS[5]) is set.
> + * Values:
> + * 0x1 (ACTIVE): Controller not idle
> + * 0x0 (IDLE): Controller is idle
> + * The function is called after returning the end of the current transfer
> + * Returns:

> + * Return 0 as controller IDLE
> + * Return a negative errno as controller ACTIVE

But why non-boolean again?

> + */
> +static int i2c_dw_is_controller_active(struct dw_i2c_dev *dev)
> +{
> +	u32 status;
> +
> +	regmap_read(dev->map, DW_IC_STATUS, &status);
> +	if (!(status & DW_IC_STATUS_MASTER_ACTIVITY))
> +		return 0;
> +
> +	return regmap_read_poll_timeout(dev->map, DW_IC_STATUS, status,
> +			!(status & DW_IC_STATUS_MASTER_ACTIVITY),
> +			1100, 20000);
> +}

...

> +	/*
> +	 * This happens rarely (~1:500) and is hard to reproduce. Debug trace
> +	 * showed that IC_STATUS had value of 0x23 when STOP_DET occurred,
> +	 * if disable IC_ENABLE.ENABLE immediately that can result in
> +	 * IC_RAW_INTR_STAT.MASTER_ON_HOLD holding SCL low. Check if
> +	 * controller is still ACTIVE before disabling I2C.
> +	 */

> +	if (i2c_dw_is_controller_active(dev))
> +		dev_err(dev->dev, "controller active\n");

No, this is rarely we skip the error code returned. Either you find the
meaningful use of the returned error code, or change to boolean.

Personally I think the latter is what we need for now.

>  	/*
>  	 * We must disable the adapter before returning and signaling the end
>  	 * of the current transfer. Otherwise the hardware might continue

-- 
With Best Regards,
Andy Shevchenko