Re: [PATCH v3] i2c: hisi: Add I2C bus recovery support

[Jie Zhan]

On 9/9/2026 10:39 AM, Bowen Yu wrote:
> When the I2C bus is stuck due to a slave device holding SDA low
> (e.g. during an incomplete transfer), the master has no way to recover
> the bus through normal operation. Add bus recovery support using the
> subctrl register to manually toggle SCL and generate clock pulses to
> release the bus.
> 
> The recovery is performed via a second register resource (sctrl_base)
> that provides direct control over SCL/SDA lines through mux and
> output-enable bits. After recovery, the I2C controller is reset through
> the ACPI _RST method and reconfigured.
> 
> Recovery is only registered when the subctrl resource is provided in
> the firmware description, keeping backward compatibility with existing
> platforms.
> 
> Signed-off-by: Bowen Yu <yubowen8@xxxxxxxxxx>
Hi Bowen,

Some minor comments inline.

Thanks!
Jie
> ---
> v2 -> v3:
> 	-Fixed function defined but not used warnings in none ACPI Scenario
> ---
>  drivers/i2c/busses/i2c-hisi.c | 145 ++++++++++++++++++++++++++++++++++
>  1 file changed, 145 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-hisi.c b/drivers/i2c/busses/i2c-hisi.c
> index ba5c9579ae19..1c90a50a9138 100644
> --- a/drivers/i2c/busses/i2c-hisi.c
> +++ b/drivers/i2c/busses/i2c-hisi.c
> @@ -5,6 +5,7 @@
>   * Copyright (c) 2021 HiSilicon Technologies Co., Ltd.
>   */
>  
> +#include <linux/acpi.h>
>  #include <linux/bits.h>
>  #include <linux/bitfield.h>
>  #include <linux/clk.h>
> @@ -62,6 +63,8 @@
>  #define HISI_I2C_INT_CLR		0x0048
>  #define HISI_I2C_INT_MASK		0x004C
>  #define HISI_I2C_TRANS_STATE		0x0050
> +#define   HISI_I2C_TRANS_STATE_SDA_LEVEL	BIT(5)
> +#define   HISI_I2C_TRANS_STATE_SCL_LEVEL	BIT(6)
>  #define HISI_I2C_TRANS_ERR		0x0054
>  #define HISI_I2C_VERSION		0x0058
>  
> @@ -86,9 +89,26 @@
>  #define NSEC_TO_CYCLES(ns, clk_rate_khz) \
>  	DIV_ROUND_UP_ULL((clk_rate_khz) * (ns), NSEC_PER_MSEC)
>  
> +/*
> + * SUBCTRL SC_I2C_CTRL register
> + * Set HISI_I2C_CTRL_DAT_CFG_EN and HISI_I2C_CTRL_SCL_CFG_EN to control
> + * I2C pin behavior by subctrl controller; use HISI_I2C_CTRL_DAT_OE and
> + * HISI_I2C_CTRL_CLK_OE to control input or output; use HISI_I2C_CTRL_SDA_OUT
> + * and HISI_I2C_CTRL_SCL_OUT to control output value.
> + */
> +#define HISI_I2C_CTRL_DAT_CFG_EN BIT(5)
> +#define HISI_I2C_CTRL_SCL_CFG_EN BIT(4)
> +#define HISI_I2C_CTRL_DAT_OE BIT(3)
> +#define HISI_I2C_CTRL_CLK_OE BIT(2)
> +#define HISI_I2C_CTRL_SDA_OUT BIT(1)
> +#define HISI_I2C_CTRL_SCL_OUT BIT(0)
> +
> +#define HISI_I2C_RECOVERY_REG_SIZE 4
> +
>  struct hisi_i2c_controller {
>  	struct i2c_adapter adapter;
>  	void __iomem *iobase;
> +	void __iomem *sctrl_addr;
>  	struct device *dev;
>  	struct clk *clk;
>  	int irq;
> @@ -108,8 +128,14 @@ struct hisi_i2c_controller {
>  	struct i2c_timings t;
>  	u32 clk_rate_khz;
>  	u32 spk_len;
> +
> +	/* Bus recovery */
> +	struct i2c_bus_recovery_info rinfo;
> +	acpi_handle acpi_handle;
>  };
>  
> +static void hisi_i2c_configure_bus(struct hisi_i2c_controller *ctlr);
> +
>  static void hisi_i2c_enable_int(struct hisi_i2c_controller *ctlr, u32 mask)
>  {
>  	writel_relaxed(mask, ctlr->iobase + HISI_I2C_INT_MASK);
> @@ -151,6 +177,121 @@ static void hisi_i2c_handle_errors(struct hisi_i2c_controller *ctlr)
>  	}
>  }
>  
> +#ifdef CONFIG_ACPI
> +static int hisi_i2c_recovery_get_scl(struct i2c_adapter *adap)
> +{
> +	struct hisi_i2c_controller *ctlr = i2c_get_adapdata(adap);
> +	u32 reg = readl(ctlr->iobase + HISI_I2C_TRANS_STATE);
> +
> +	return !!(reg & HISI_I2C_TRANS_STATE_SCL_LEVEL);
> +}
> +
> +static int hisi_i2c_recovery_get_sda(struct i2c_adapter *adap)
> +{
> +	struct hisi_i2c_controller *ctlr = i2c_get_adapdata(adap);
> +	u32 reg = readl(ctlr->iobase + HISI_I2C_TRANS_STATE);
> +
> +	return !!(reg & HISI_I2C_TRANS_STATE_SDA_LEVEL);
> +}
> +
> +static void hisi_i2c_recovery_set_scl(struct i2c_adapter *adap, int val)
> +{
> +	struct hisi_i2c_controller *ctlr = i2c_get_adapdata(adap);
> +	u32 reg;
> +
> +	reg = readl(ctlr->sctrl_addr);
> +	if (val)
> +		reg |= HISI_I2C_CTRL_SCL_OUT;
> +	else
> +		reg &= ~HISI_I2C_CTRL_SCL_OUT;
> +	writel(reg, ctlr->sctrl_addr);
> +}
> +
> +static void hisi_i2c_prepare_recovery(struct i2c_adapter *adap)
> +{
> +	struct hisi_i2c_controller *ctlr = i2c_get_adapdata(adap);
> +	u32 reg;
> +
> +	reg = readl(ctlr->sctrl_addr);
> +	reg |= HISI_I2C_CTRL_SCL_CFG_EN | HISI_I2C_CTRL_DAT_CFG_EN |
> +		   HISI_I2C_CTRL_CLK_OE | HISI_I2C_CTRL_SCL_OUT;
> +	reg &= ~HISI_I2C_CTRL_DAT_OE;
> +	writel(reg, ctlr->sctrl_addr);
> +}
> +
> +static void hisi_i2c_unprepare_recovery(struct i2c_adapter *adap)
> +{
> +	struct hisi_i2c_controller *ctlr = i2c_get_adapdata(adap);
> +	u32 reg;
> +
> +	reg = readl(ctlr->sctrl_addr);
> +	reg &= ~(HISI_I2C_CTRL_SCL_CFG_EN | HISI_I2C_CTRL_DAT_CFG_EN);
> +	writel(reg, ctlr->sctrl_addr);
> +
> +	/*
> +	 * Invokes the specific ACPI method "_RST" to trigger a soft reset
> +	 * of the I2C controller to help the I2C controller recover from
> +	 * the abnormal state after the bus recovery process.
> +	 */
> +	if (ctlr->acpi_handle && acpi_has_method(ctlr->acpi_handle, "_RST")) {
> +		acpi_status status;
> +
> +		status = acpi_evaluate_object(ctlr->acpi_handle, "_RST", NULL, NULL);
> +		if (ACPI_FAILURE(status))
> +			dev_err(ctlr->dev, "_RST method failed: %s\n",
> +				acpi_format_exception(status));
> +	}
> +	hisi_i2c_configure_bus(ctlr);
> +}
> +
> +static int hisi_i2c_get_bus_recovery_res(struct hisi_i2c_controller *ctlr,
> +					 struct platform_device *pdev)
> +{
> +	struct resource *res0;
> +
> +	res0 = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> +
> +	if (!res0 || resource_size(res0) != HISI_I2C_RECOVERY_REG_SIZE)
> +		return -ENODEV;
> +
> +	ctlr->sctrl_addr = devm_ioremap_resource(&pdev->dev, res0);
> +	if (IS_ERR(ctlr->sctrl_addr)) {
> +		ctlr->sctrl_addr = NULL;
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +static int hisi_i2c_recovery_init(struct hisi_i2c_controller *ctlr)
> +{
> +	struct platform_device *pdev = to_platform_device(ctlr->dev);
> +	struct i2c_adapter *adapter = &ctlr->adapter;
> +	int ret;
> +
> +	if (acpi_disabled)
> +		return -ENODEV;
Is #ifdef CONFIG_ACPI still useful if 'acpi_disabled' is checked?
> +
> +	ret = hisi_i2c_get_bus_recovery_res(ctlr, pdev);
> +	if (ret)
> +		return ret;
> +
> +	ctlr->rinfo = (struct i2c_bus_recovery_info){
Neat: (struct i2c_bus_recovery_info) {
Good to add a space.
> +		.get_scl = hisi_i2c_recovery_get_scl,
> +		.get_sda = hisi_i2c_recovery_get_sda,
> +		.set_scl = hisi_i2c_recovery_set_scl,
> +		.prepare_recovery = hisi_i2c_prepare_recovery,
> +		.unprepare_recovery = hisi_i2c_unprepare_recovery,
> +		.recover_bus = i2c_generic_scl_recovery,
> +	};
> +	adapter->bus_recovery_info = &ctlr->rinfo;
> +	ctlr->acpi_handle = ACPI_HANDLE(ctlr->dev);
Neat: a blank line before return 0.
> +	return 0;
> +}
> +#else
> +static int hisi_i2c_recovery_init(struct hisi_i2c_controller *ctlr) { return -ENODEV; }
> +#endif /* CONFIG_ACPI */
> +
>  static int hisi_i2c_start_xfer(struct hisi_i2c_controller *ctlr)
>  {
>  	struct i2c_msg *msg = ctlr->msgs;
> @@ -504,6 +645,10 @@ static int hisi_i2c_probe(struct platform_device *pdev)
>  	adapter->dev.parent = dev;
>  	i2c_set_adapdata(adapter, ctlr);
>  
> +	ret = hisi_i2c_recovery_init(ctlr);
> +	if (ret)
> +		dev_info(ctlr->dev, "I2C bus recovery not available\n");
> +
Move this before setting 'adapter' and i2c_set_adapdata()?

Recovery init should be done before the final preparation of 'adapter'.
>  	ret = devm_i2c_add_adapter(dev, adapter);
>  	if (ret)
>  		return ret;