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Date:   Tue, 22 Jan 2019 23:12:06 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com,
        mkarthik@...dia.com, smohammed@...dia.com, talho@...dia.com
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH V3] i2c: tegra: Add Bus Clear Master Support

22.01.2019 23:02, Sowjanya Komatineni пишет:
> 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.
> 
> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
> ---
>  [V3]: Updated comments and commit message to be clear on the change
>  [V2]: Same as V1 rebased to 5.0-rc1
> 
>  drivers/i2c/busses/i2c-tegra.c | 70 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index e417ebf7628c..b1b920b4a203 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -54,6 +54,7 @@
>  #define I2C_FIFO_STATUS_RX_SHIFT		0
>  #define I2C_INT_MASK				0x064
>  #define I2C_INT_STATUS				0x068
> +#define I2C_INT_BUS_CLR_DONE			BIT(11)
>  #define I2C_INT_PACKET_XFER_COMPLETE		BIT(7)
>  #define I2C_INT_ALL_PACKETS_XFER_COMPLETE	BIT(6)
>  #define I2C_INT_TX_FIFO_OVERFLOW		BIT(5)
> @@ -96,6 +97,15 @@
>  #define I2C_HEADER_MASTER_ADDR_SHIFT		12
>  #define I2C_HEADER_SLAVE_ADDR_SHIFT		1
>  
> +#define I2C_BUS_CLEAR_CNFG			0x084
> +#define I2C_BC_SCLK_THRESHOLD			9
> +#define I2C_BC_SCLK_THRESHOLD_SHIFT		16
> +#define I2C_BC_STOP_COND			BIT(2)
> +#define I2C_BC_TERMINATE			BIT(1)
> +#define I2C_BC_ENABLE				BIT(0)
> +#define I2C_BUS_CLEAR_STATUS			0x088
> +#define I2C_BC_STATUS				BIT(0)
> +
>  #define I2C_CONFIG_LOAD				0x08C
>  #define I2C_MSTR_CONFIG_LOAD			BIT(0)
>  #define I2C_SLV_CONFIG_LOAD			BIT(1)
> @@ -155,6 +165,8 @@ enum msg_end_type {
>   * @has_mst_fifo: The I2C controller contains the new MST FIFO interface that
>   *		provides additional features and allows for longer messages to
>   *		be transferred in one go.
> + * @supports_bus_clear: Bus Clear support to recover from bus hang during
> + *		SDA stuck low from device for some unknown reasons.
>   */
>  struct tegra_i2c_hw_feature {
>  	bool has_continue_xfer_support;
> @@ -167,6 +179,7 @@ struct tegra_i2c_hw_feature {
>  	bool has_multi_master_mode;
>  	bool has_slcg_override_reg;
>  	bool has_mst_fifo;
> +	bool supports_bus_clear;
>  };
>  
>  /**
> @@ -639,6 +652,12 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>  			i2c_dev->msg_err |= I2C_ERR_ARBITRATION_LOST;
>  		goto err;
>  	}
> +	/*
> +	 * I2C transfer is terminated during the bus clear so skip
> +	 * processing the other interrupts.
> +	 */
> +	if (i2c_dev->hw->supports_bus_clear && (status & I2C_INT_BUS_CLR_DONE))
> +		goto err;
>  
>  	if (i2c_dev->msg_read && (status & I2C_INT_RX_FIFO_DATA_REQ)) {
>  		if (i2c_dev->msg_buf_remaining)
> @@ -668,6 +687,8 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>  	tegra_i2c_mask_irq(i2c_dev, I2C_INT_NO_ACK | I2C_INT_ARBITRATION_LOST |
>  		I2C_INT_PACKET_XFER_COMPLETE | I2C_INT_TX_FIFO_DATA_REQ |
>  		I2C_INT_RX_FIFO_DATA_REQ);
> +	if (i2c_dev->hw->supports_bus_clear)
> +		tegra_i2c_mask_irq(i2c_dev, I2C_INT_BUS_CLR_DONE);
>  	i2c_writel(i2c_dev, status, I2C_INT_STATUS);
>  	if (i2c_dev->is_dvc)
>  		dvc_writel(i2c_dev, DVC_STATUS_I2C_DONE_INTR, DVC_STATUS);
> @@ -678,6 +699,43 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>  	return IRQ_HANDLED;
>  }
>  
> +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) {
> +		reinit_completion(&i2c_dev->msg_complete);
> +		reg = (I2C_BC_SCLK_THRESHOLD << I2C_BC_SCLK_THRESHOLD_SHIFT) |
> +		      I2C_BC_STOP_COND | I2C_BC_TERMINATE;
> +		i2c_writel(i2c_dev, reg, I2C_BUS_CLEAR_CNFG);
> +		if (i2c_dev->hw->has_config_load_reg) {
> +			err = tegra_i2c_wait_for_config_load(i2c_dev);
> +			if (err)
> +				return err;
> +		}
> +		reg |= I2C_BC_ENABLE;
> +		i2c_writel(i2c_dev, reg, I2C_BUS_CLEAR_CNFG);
> +		tegra_i2c_unmask_irq(i2c_dev, I2C_INT_BUS_CLR_DONE);
> +
> +		time_left = wait_for_completion_timeout(&i2c_dev->msg_complete,
> +							TEGRA_I2C_TIMEOUT);
> +		if (time_left == 0) {
> +			dev_err(i2c_dev->dev, "timed out for bus clear\n");
> +			return -ETIMEDOUT;
> +		}
> +		reg = i2c_readl(i2c_dev, I2C_BUS_CLEAR_STATUS);
> +		if (!(reg & I2C_BC_STATUS)) {
> +			dev_err(i2c_dev->dev,
> +				"Un-recovered arbitration lost\n");
> +			return -EIO;
> +		}
> +	}
> +
> +	return -EAGAIN;
> +}
> +
>  static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
>  	struct i2c_msg *msg, enum msg_end_type end_state)
>  {
> @@ -759,6 +817,12 @@ 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);
> +		return -EAGAIN;

This changes the returned errno from -EIO to -EAGAIN for the supports_bus_clear=false case, is it okay and intentional?

[snip]

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