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

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Date:   Mon, 11 Feb 2019 20:18:15 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>,
        "Shardar Mohammed" <smohammed@...dia.com>,
        Timo Alho <talho@...dia.com>,
        "peda@...ntia.se" <peda@...ntia.se>,
        "digetx@...il.com" <digetx@...il.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH V18 2/6] i2c: tegra: add bus clear Master Support

> > 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.
>
>
OK, Will update to use i2c_bus_recovery_info

Sowjanya