linux-kernel - Re: [PATCH v2] i2c: designware: fix __i2c_dw_disable() in case master is holding SCL low

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Message-ID: <ZOODfgHq5BXDZnzG@smile.fi.intel.com>
Date:   Mon, 21 Aug 2023 18:32:14 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yann Sionneau <yann@...nneau.net>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yann Sionneau <ysionneau@...ray.eu>,
        Jonathan Borne <jborne@...ray.eu>
Subject: Re: [PATCH v2] i2c: designware: fix __i2c_dw_disable() in case
 master is holding SCL low

On Mon, Aug 21, 2023 at 04:01:03PM +0200, Yann Sionneau wrote:
> From: Yann Sionneau <ysionneau@...ray.eu>
> 
> The DesignWare IP can be synthesized with the IC_EMPTYFIFO_HOLD_MASTER_EN
> parameter.
> In this case, when the TX FIFO gets empty and the last command didn't have
> the STOP bit (IC_DATA_CMD[9]), the controller will hold SCL low until
> a new command is pushed into the TX FIFO or the transfer is aborted.
> 
> When the controller is holding SCL low, it cannot be disabled.
> The transfer must first be aborted.
> Also, the bus recovery won't work because SCL is held low by the master.
> 
> Check if the master is holding SCL low in __i2c_dw_disable() before trying
> to disable the controller. If SCL is held low, an abort is initiated.
> When the abort is done, then proceed with disabling the controller.
> 
> This whole situation can happen for instance during SMBus read data block
> if the slave just responds with "byte count == 0".
> This puts the driver in an unrecoverable state, because the controller is
> holding SCL low and the current __i2c_dw_disable() procedure is not
> working. In this situation only a SoC reset can fix the i2c bus.

Thank you for an update!
My comments below.

...

>  void __i2c_dw_disable(struct dw_i2c_dev *dev)
>  {
> -	int timeout = 100;

I would leave this untouched to make patch less invasive and
easier to backport.

> +	unsigned int raw_intr_stats;
> +	bool abort_done = false;
> +	int abort_timeout = 100;
> +	int dis_timeout = 100;
> +	unsigned int enable;
> +	bool abort_needed;
>  	u32 status;
>  
> +	regmap_read(dev->map, DW_IC_RAW_INTR_STAT, &raw_intr_stats);
> +	regmap_read(dev->map, DW_IC_ENABLE, &enable);
> +
> +	abort_needed = raw_intr_stats & DW_IC_INTR_MST_ON_HOLD;

> +

This blank line is not needed.

> +	if (abort_needed) {
> +		regmap_write(dev->map, DW_IC_ENABLE, enable | DW_IC_ENABLE_ABORT);

> +		do {
> +			regmap_read(dev->map, DW_IC_ENABLE, &enable);
> +			abort_done = !(enable & DW_IC_ENABLE_ABORT);
> +			usleep_range(10, 20);
> +		} while (!abort_done && abort_timeout--);

Now as you split this loop, it may be replaced by regmap_read_poll_timeout()
call.

> +		if (!abort_done)
> +			dev_err(dev->dev, "timeout while trying to abort current transfer\n");
> +	}

...

Other than above, looks good to me.

-- 
With Best Regards,
Andy Shevchenko