linux-kernel - Re: [PATCH V18 2/6] i2c: tegra: add bus clear Master Support

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Message-ID: <20190211124431.kys66uzp5hwa5ret@ninjato>
Date:   Mon, 11 Feb 2019 13:44:32 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Sowjanya Komatineni <skomatineni@...dia.com>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com,
        mkarthik@...dia.com, smohammed@...dia.com, talho@...dia.com,
        peda@...ntia.se, digetx@...il.com, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH V18 2/6] i2c: tegra: add bus clear Master Support

Hi,

On Fri, Feb 08, 2019 at 10:59:38AM -0800, Sowjanya Komatineni wrote:
> Bus clear feature of Tegra I2C controller helps to recover from
> bus hang when I2C master loses the bus arbitration due to the
> slave device holding SDA LOW continuously for some unknown reasons.
> 
> Per I2C specification, the device that held the bus LOW should
> release it within 9 clock pulses.
> 
> During bus clear operation, Tegra I2C controller sends 9 clock
> pulses and terminates the transaction with STOP condition.
> Upon successful bus clear operation, bus goes to idle state and
> driver retries the transaction.
> 
> Acked-by: Thierry Reding <treding@...dia.com>
> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>

We have a bus recovery infrastructure in the core. Tying your code into
it should be easy. You probably just need a 'struct
i2c_bus_recovery_info', populate the 'recover_bus' callback with
'tegra_i2c_issue_bus_clear()', and attach this struct to the 'struct
adapter' if the IP core supports bus recovery, otherwise leave it empty.
Then, you can...

> +static int tegra_i2c_issue_bus_clear(struct tegra_i2c_dev *i2c_dev)
> +{
> +	int err;
> +	unsigned long time_left;
> +	u32 reg;
> +
> +	if (i2c_dev->hw->supports_bus_clear) {

... remove the if here because the core will check for a valid
i2c_bus_recovery_info...

> @@ -759,6 +818,13 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>  		return 0;
>  
>  	tegra_i2c_init(i2c_dev);
> +	/* start recovery upon arbitration loss in single master mode */
> +	if (i2c_dev->msg_err == I2C_ERR_ARBITRATION_LOST) {
> +		if (!i2c_dev->is_multimaster_mode)
> +			return tegra_i2c_issue_bus_clear(i2c_dev);

... and use simply i2c_recover_bus() here.

This will help making bus recovery use consistent across drivers.

Thanks,

   Wolfram

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