[v3,2/2] i2c: spacemit: add support for SpacemiT K1 SoC

From: Troy Mitchell <troymitchell988@gmail.com>

This patch introduces basic I2C support for the SpacemiT K1 SoC,
utilizing interrupts for transfers.

The driver has been tested using i2c-tools on a Bananapi-F3 board,
and basic I2C read/write operations have been confirmed to work.

Signed-off-by: Troy Mitchell <TroyMitchell988@gmail.com>
---
 drivers/i2c/busses/Kconfig  |  19 ++
 drivers/i2c/busses/Makefile |   1 +
 drivers/i2c/busses/i2c-k1.c | 656 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 676 insertions(+)

On 11:07 Tue 12 Nov     , Troy Mitchell wrote:
> From: Troy Mitchell <troymitchell988@gmail.com>
> 
> This patch introduces basic I2C support for the SpacemiT K1 SoC,
> utilizing interrupts for transfers.
> 
> The driver has been tested using i2c-tools on a Bananapi-F3 board,
> and basic I2C read/write operations have been confirmed to work.
> 
> Signed-off-by: Troy Mitchell <TroyMitchell988@gmail.com>
> ---
>  drivers/i2c/busses/Kconfig  |  19 ++
>  drivers/i2c/busses/Makefile |   1 +
>  drivers/i2c/busses/i2c-k1.c | 656 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 676 insertions(+)
> 
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index 6b3ba7e5723a..91630f55667f 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -779,6 +779,25 @@ config I2C_JZ4780
>  
>  	 If you don't know what to do here, say N.
>  
> +config I2C_K1
> +	tristate "Spacemit K1 I2C adapter"
> +	depends on ARCH_SPACEMIT || COMPILE_TEST
> +	depends on OF
> +	help
> +	  This option enables support for the I2C interface on the Spacemit K1
> +	  platform.
> +
> +	  If you enable this configuration, the kernel will include support for
> +	  the I2C adapter specific to the Spacemit K1 platform. This driver ca
> +	  be used to manage I2C bus transactions, which are necessary for
> +	  interfacing with I2C peripherals such as sensors, EEPROMs, and other
> +	  devices.
> +
> +	  This driver can also be compiled as a module. If you choose to build
> +	  it as a module, the resulting kernel module will be named `i2c-k1`.
> +	  Loading this module will enable the I2C functionality for the K1
> +	  platform dynamically, without requiring a rebuild of the kernel.
> +
>  config I2C_KEBA
>  	tristate "KEBA I2C controller support"
>  	depends on HAS_IOMEM
> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
> index ecc07c50f2a0..9744b0e58598 100644
> --- a/drivers/i2c/busses/Makefile
> +++ b/drivers/i2c/busses/Makefile
> @@ -76,6 +76,7 @@ obj-$(CONFIG_I2C_IMX)		+= i2c-imx.o
>  obj-$(CONFIG_I2C_IMX_LPI2C)	+= i2c-imx-lpi2c.o
>  obj-$(CONFIG_I2C_IOP3XX)	+= i2c-iop3xx.o
>  obj-$(CONFIG_I2C_JZ4780)	+= i2c-jz4780.o
> +obj-$(CONFIG_I2C_K1)		+= i2c-k1.o
>  obj-$(CONFIG_I2C_KEBA)		+= i2c-keba.o
>  obj-$(CONFIG_I2C_KEMPLD)	+= i2c-kempld.o
>  obj-$(CONFIG_I2C_LPC2K)		+= i2c-lpc2k.o
> diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
> new file mode 100644
> index 000000000000..12bb71625e0a
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-k1.c
> @@ -0,0 +1,656 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2024 Troy Mitchell <troymitchell988@gmail.com>
> + */
> +
> + #include <linux/clk.h>
> + #include <linux/i2c.h>
> + #include <linux/iopoll.h>
> + #include <linux/module.h>
> + #include <linux/of_address.h>
> + #include <linux/platform_device.h>
> +
> +/* spacemit i2c registers */
> +#define ICR          0x0		/* Control Register */
> +#define ISR          0x4		/* Status Register */
> +#define ISAR         0x8		/* Slave Address Register */
> +#define IDBR         0xc		/* Data Buffer Register */
> +#define ILCR         0x10		/* Load Count Register */
> +#define IWCR         0x14		/* Wait Count Register */
> +#define IRST_CYC     0x18		/* Bus reset cycle counter */
> +#define IBMR         0x1c		/* Bus monitor register */
> +#define IWFIFO       0x20		/* Write FIFO Register */
> +#define IWFIFO_WPTR  0x24		/* Write FIFO Write Pointer Register */
> +#define IWFIFO_RPTR  0x28		/* Write FIFO Read Pointer Register */
> +#define IRFIFO       0x2c		/* Read FIFO Register */
> +#define IRFIFO_WPTR  0x30		/* Read FIFO Write Pointer Register */
> +#define IRFIFO_RPTR  0x34		/* Read FIFO Read Pointer Register */
> +
> +/* register ICR fields */
> +#define CR_START        BIT(0)		/* start bit */
> +#define CR_STOP         BIT(1)		/* stop bit */
> +#define CR_ACKNAK       BIT(2)		/* send ACK(0) or NAK(1) */
> +#define CR_TB           BIT(3)		/* transfer byte bit */
> +#define CR_TXBEGIN      BIT(4)		/* transaction begin */
> +#define CR_FIFOEN       BIT(5)		/* enable FIFO mode */
> +#define CR_GPIOEN       BIT(6)		/* enable GPIO mode for SCL in HS */
> +#define CR_DMAEN        BIT(7)		/* enable DMA for TX and RX FIFOs */
> +#define CR_MODE_FAST    BIT(8)		/* bus mode (master operation) */
> +#define CR_MODE_HIGH    BIT(9)		/* bus mode (master operation) */
> +#define CR_UR           BIT(10)		/* unit reset */
> +#define CR_RSTREQ       BIT(11)		/* i2c bus reset request */
> +#define CR_MA           BIT(12)		/* master abort */
> +#define CR_SCLE         BIT(13)		/* master clock enable */
> +#define CR_IUE          BIT(14)		/* unit enable */
> +#define CR_HS_STRETCH   BIT(16)		/* I2C hs stretch */
> +#define CR_ALDIE        BIT(18)		/* enable arbitration interrupt */
> +#define CR_DTEIE        BIT(19)		/* enable tx interrupts */
> +#define CR_DRFIE        BIT(20)		/* enable rx interrupts */
> +#define CR_GCD          BIT(21)		/* general call disable */
> +#define CR_BEIE         BIT(22)		/* enable bus error ints */
> +#define CR_SADIE        BIT(23)		/* slave address detected int enable */
> +#define CR_SSDIE        BIT(24)		/* slave STOP detected int enable */
> +#define CR_MSDIE        BIT(25)		/* master STOP detected int enable */
> +#define CR_MSDE         BIT(26)		/* master STOP detected enable */
> +#define CR_TXDONEIE     BIT(27)		/* transaction done int enable */
> +#define CR_TXEIE        BIT(28)		/* transmit FIFO empty int enable */
> +#define CR_RXHFIE       BIT(29)		/* receive FIFO half-full int enable */
> +#define CR_RXFIE        BIT(30)		/* receive FIFO full int enable */
> +#define CR_RXOVIE       BIT(31)		/* receive FIFO overrun int enable */
> +
> +/* register ISR fields */
> +#define SR_RWM          BIT(13)		/* read/write mode */
> +#define SR_ACKNAK       BIT(14)		/* ACK/NACK status */
> +#define SR_UB           BIT(15)		/* unit busy */
> +#define SR_IBB          BIT(16)		/* i2c bus busy */
> +#define SR_EBB          BIT(17)		/* early bus busy */
> +#define SR_ALD          BIT(18)		/* arbitration loss detected */
> +#define SR_ITE          BIT(19)		/* tx buffer empty */
> +#define SR_IRF          BIT(20)		/* rx buffer full */
> +#define SR_GCAD         BIT(21)		/* general call address detected */
> +#define SR_BED          BIT(22)		/* bus error no ACK/NAK */
> +#define SR_SAD          BIT(23)		/* slave address detected */
> +#define SR_SSD          BIT(24)		/* slave stop detected */
> +#define SR_MSD          BIT(26)		/* master stop detected */
> +#define SR_TXDONE       BIT(27)		/* transaction done */
> +#define SR_TXE          BIT(28)		/* tx FIFO empty */
> +#define SR_RXHF         BIT(29)		/* rx FIFO half-full */
> +#define SR_RXF          BIT(30)		/* rx FIFO full */
> +#define SR_RXOV         BIT(31)		/* RX FIFO overrun */
> +
> +/* register ILCR fields */
> +#define LCR_SLV         0x000001FF	/* SLV: bit[8:0] */
> +#define LCR_FLV         0x0003FE00	/* FLV: bit[17:9] */
> +#define LCR_HLVH        0x07FC0000	/* HLVH: bit[26:18] */
> +#define LCR_HLVL        0xF8000000	/* HLVL: bit[31:27] */
> +
> +/* register IWCR fields */
> +#define WCR_COUNT       0x0000001F	/* COUNT: bit[4:0] */
> +#define WCR_COUNT1      0x000003E0	/* HS_COUNT1: bit[9:5] */
> +#define WCR_COUNT2      0x00007C00	/* HS_COUNT2: bit[14:10] */
> +
> +/* register IBMR fields */
> +#define BMR_SDA         BIT(0)		/* SDA line level */
> +#define BMR_SCL         BIT(1)		/* SCL line level */
> +
> +/* register IWFIFO fields */
> +#define WFIFO_DATA_MSK      0x000000FF  /* data: bit[7:0] */
> +#define WFIFO_CTRL_MSK      0x000003E0  /* control: bit[11:8] */
> +#define WFIFO_CTRL_START    BIT(8)      /* start bit */
> +#define WFIFO_CTRL_STOP     BIT(9)      /* stop bit */
> +#define WFIFO_CTRL_ACKNAK   BIT(10)     /* send ACK(0) or NAK(1) */
> +#define WFIFO_CTRL_TB       BIT(11)     /* transfer byte bit */
> +
> +/* status register init value */
> +#define I2C_INT_STATUS_MASK    0xfffc0000  /* SR bits[31:18] */
> +#define I2C_INT_CTRL_MASK      (CR_ALDIE | CR_DTEIE | CR_DRFIE | \
> +				CR_BEIE | CR_TXDONEIE | CR_TXEIE | \
> +				CR_RXHFIE | CR_RXFIE | CR_RXOVIE | \
> +				CR_MSDIE)
> +
> +/* i2c bus recover timeout: us */
> +#define I2C_BUS_RECOVER_TIMEOUT		(100000)
> +
> +#define I2C_FAST_MODE_FREQ		(400000)
> +
> +enum spacemit_i2c_state {
> +	STATE_IDLE,
> +	STATE_START,
> +	STATE_READ,
> +	STATE_WRITE,
> +};
> +
> +enum spacemit_i2c_dir {
> +	DIR_WRITE,
> +	DIR_READ
> +};
> +
> +/* i2c-spacemit driver's main struct */
> +struct spacemit_i2c_dev {
> +	struct device *dev;
> +	struct i2c_adapter adapt;
> +
> +	/* hardware resources */
> +	void __iomem *base;
> +	int irq;
> +
> +	struct i2c_msg *msgs;
> +	int msg_num;
> +	struct i2c_msg *cur_msg;
> +
> +	/* index of the current message being processed */
> +	int msg_idx;
> +	u8 *msg_buf;
> +	/* the number of unprocessed bytes remaining in each message  */
> +	size_t unprocessed;
> +
> +	enum spacemit_i2c_state state;
> +	enum spacemit_i2c_dir dir;
> +	struct completion complete;
> +	u32 status;
> +	u32 err;
> +};
> +
> +static void spacemit_i2c_enable(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 val;
> +
> +	val = readl(i2c->base + ICR);
> +	writel(val | CR_IUE, i2c->base + ICR);
> +}
> +
> +static void spacemit_i2c_disable(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 val;
> +
> +	val = readl(i2c->base + ICR);
> +	val &= ~CR_IUE;
> +	writel(val, i2c->base + ICR);
> +}
> +
> +static void spacemit_i2c_reset(struct spacemit_i2c_dev *i2c)
> +{
> +	writel(CR_UR, i2c->base + ICR);
> +	udelay(5);
> +	writel(0, i2c->base + ICR);
> +}
> +
> +static int spacemit_i2c_handle_err(struct spacemit_i2c_dev *i2c);
> +
> +static void spacemit_i2c_bus_reset(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 status;
> +
> +	/* if bus is locked, reset unit. 0: locked */
> +	status = readl(i2c->base + IBMR);
> +	if ((status & BMR_SDA) && (status & BMR_SCL))
> +		return;
> +
> +	spacemit_i2c_reset(i2c);
> +	usleep_range(10, 20);
> +
> +	/* check scl status again */
> +	status = readl(i2c->base + IBMR);
> +	if (!(status & BMR_SCL))
> +		dev_warn_ratelimited(i2c->dev, "unit reset failed\n");
> +}
> +
> +static int spacemit_i2c_recover_bus_busy(struct spacemit_i2c_dev *i2c)
> +{
> +	int ret = 0;
> +	u32 val;
> +
> +	val = readl(i2c->base + ISR);
> +	if (likely(!(val & (SR_UB | SR_IBB))))
> +		return 0;
> +
> +	ret = readl_poll_timeout(i2c->base + ISR, val, !(val & (SR_UB | SR_IBB)),
> +				 1500, I2C_BUS_RECOVER_TIMEOUT);
> +	if (unlikely(ret)) {
> +		spacemit_i2c_reset(i2c);
> +		ret = -EAGAIN;
> +	}
> +
> +	return ret;
> +}
> +
> +static void spacemit_i2c_check_bus_release(struct spacemit_i2c_dev *i2c)
> +{
> +	/* in case bus is not released after transfer completes */
> +	if (unlikely(readl(i2c->base + ISR) & SR_EBB)) {
> +		spacemit_i2c_bus_reset(i2c);
> +		usleep_range(90, 150);
> +	}
> +}
> +
> +static void spacemit_i2c_init(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 val = 0;
> +
> +	/*
> +	 * Unmask interrupt bits for all xfer mode:
> +	 * bus error, arbitration loss detected.
> +	 * For transaction complete signal, we use master stop
> +	 * interrupt, so we don't need to unmask CR_TXDONEIE.
> +	 */
> +	val |= CR_BEIE | CR_ALDIE;
> +
> +	/*
> +	 * Unmask interrupt bits for interrupt xfer mode:
> +	 * DBR rx full.
> +	 * For tx empty interrupt CR_DTEIE, we only
> +	 * need to enable when trigger byte transfer to start
> +	 * data sending.
> +	 */
> +	val |= CR_DRFIE;
> +
> +	/* set speed bits: default fast mode */
> +	val |= CR_MODE_FAST;
> +
> +	/* disable response to general call */
> +	val |= CR_GCD;
> +
> +	/* enable SCL clock output */
> +	val |= CR_SCLE;
> +
> +	/* enable master stop detected */
> +	val |= CR_MSDE | CR_MSDIE;
> +
> +	writel(val, i2c->base + ICR);
> +}
> +
> +static inline void
> +spacemit_i2c_clear_int_status(struct spacemit_i2c_dev *i2c, u32 mask)
> +{
> +	writel(mask & I2C_INT_STATUS_MASK, i2c->base + ISR);
> +}
> +
> +static void spacemit_i2c_start(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 slave_addr_rw, val;
> +
> +	i2c->dir = i2c->cur_msg->flags & I2C_M_RD;
> +	i2c->state = STATE_START;
> +
> +	if (i2c->cur_msg->flags & I2C_M_RD)
> +		slave_addr_rw = ((i2c->cur_msg->addr & 0x7f) << 1) | 1;
> +	else
> +		slave_addr_rw = (i2c->cur_msg->addr & 0x7f) << 1;
> +
> +	writel(slave_addr_rw, i2c->base + IDBR);
> +
> +	val = readl(i2c->base + ICR);
> +
> +	/* send start pulse */
> +	val &= ~CR_STOP;
> +	val |= CR_START | CR_TB | CR_DTEIE;
> +	writel(val, i2c->base + ICR);
> +}
> +
> +static void spacemit_i2c_stop(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 val;
> +
> +	val = readl(i2c->base + ICR);
> +
> +	val |= CR_STOP | CR_ALDIE | CR_TB;
> +
> +	if (i2c->dir == DIR_READ)
> +		val |= CR_ACKNAK;
> +
> +	writel(val, i2c->base + ICR);
> +}
> +
> +static int spacemit_i2c_xfer_msg(struct spacemit_i2c_dev *i2c)
> +{
> +	unsigned long time_left;
> +
> +	for (i2c->msg_idx = 0; i2c->msg_idx < i2c->msg_num; i2c->msg_idx++) {
> +		i2c->cur_msg = i2c->msgs + i2c->msg_idx;
> +		i2c->msg_buf = i2c->cur_msg->buf;
> +		i2c->err = 0;
> +		i2c->status = 0;
> +		i2c->unprocessed = i2c->cur_msg->len;
> +
> +		reinit_completion(&i2c->complete);
> +
> +		spacemit_i2c_start(i2c);
> +
> +		time_left = wait_for_completion_timeout(&i2c->complete,
> +							i2c->adapt.timeout);
> +		if (unlikely(time_left == 0)) {
> +			dev_alert(i2c->dev, "msg completion timeout\n");
> +			spacemit_i2c_bus_reset(i2c);
> +			spacemit_i2c_reset(i2c);
> +			return -ETIMEDOUT;
> +		}
> +
> +		if (unlikely(i2c->err))
> +			return spacemit_i2c_handle_err(i2c);
> +	}
> +
> +	return 0;
> +}
> +
> +static int spacemit_i2c_is_last_msg(struct spacemit_i2c_dev *i2c)
> +{
> +	if (i2c->dir == DIR_READ) {
> +		if (i2c->unprocessed == 1 && i2c->msg_idx == i2c->msg_num - 1)
> +			return 1;
> +	} else if (i2c->dir == DIR_WRITE) {
> +		if (!i2c->unprocessed && i2c->msg_idx == i2c->msg_num - 1)
> +			return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +static void spacemit_i2c_handle_write(struct spacemit_i2c_dev *i2c)
> +{
> +	/* if transfer completes, ISR will handle it */
> +	if (i2c->status & SR_MSD)
> +		return;
> +
> +	if (i2c->unprocessed) {
> +		writel(*i2c->msg_buf++, i2c->base + IDBR);
> +		i2c->unprocessed--;
> +		return;
> +	}
> +
> +	/* STATE_IDLE avoids trigger next byte */
> +	i2c->state = STATE_IDLE;
> +	complete(&i2c->complete);
> +}
> +
> +static void spacemit_i2c_handle_read(struct spacemit_i2c_dev *i2c)
> +{
> +	if (i2c->unprocessed) {
> +		*i2c->msg_buf++ = readl(i2c->base + IDBR);
> +		i2c->unprocessed--;
> +	}
> +
> +	/* if transfer completes, ISR will handle it */
> +	if (i2c->status & (SR_MSD | SR_ACKNAK))
> +		return;
> +
> +	/* it has to append stop bit in icr that read last byte */
> +	if (i2c->unprocessed)
> +		return;
> +
> +	/* STATE_IDLE avoids trigger next byte */
> +	i2c->state = STATE_IDLE;
> +	complete(&i2c->complete);
> +}
> +
> +static void spacemit_i2c_handle_start(struct spacemit_i2c_dev *i2c)
> +{
> +	if (i2c->dir == DIR_READ) {
> +		i2c->state = STATE_READ;
> +		return;
> +	}
> +
> +	if (i2c->dir == DIR_WRITE) {
> +		i2c->state = STATE_WRITE;
> +		spacemit_i2c_handle_write(i2c);
> +	}
> +}
> +
> +static int spacemit_i2c_handle_err(struct spacemit_i2c_dev *i2c)
> +{
> +	if (!i2c->err)
> +		return 0;
> +
> +	dev_dbg(i2c->dev, "i2c error status: 0x%08x\n",	i2c->status);
> +
> +	if (i2c->err & (SR_BED | SR_ALD))
> +		spacemit_i2c_reset(i2c);
> +
> +	if (i2c->err & (SR_RXOV | SR_ALD))
> +		return -EAGAIN;
> +
> +	return (i2c->status & SR_ACKNAK) ? -ENXIO : -EIO;
> +}
> +
> +static void spacemit_i2c_err_check(struct spacemit_i2c_dev *i2c)
> +{
> +	u32 val;
> +	/*
> +	 * send transaction complete signal:
> +	 * error happens, detect master stop
> +	 */
> +	if (likely(i2c->err || (i2c->status & SR_MSD))) {
> +		/*
> +		 * Here the transaction is already done, we don't need any
> +		 * other interrupt signals from now, in case any interrupt
> +		 * happens before spacemit_i2c_xfer to disable irq and i2c unit,
> +		 * we mask all the interrupt signals and clear the interrupt
> +		 * status.
> +		 */
> +		val = readl(i2c->base + ICR);
> +		val &= ~I2C_INT_CTRL_MASK;
> +		writel(val, i2c->base + ICR);
> +
> +		spacemit_i2c_clear_int_status(i2c, I2C_INT_STATUS_MASK);
> +
> +		i2c->state = STATE_IDLE;
> +		complete(&i2c->complete);
> +	}
> +}
> +
> +static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
> +{
> +	struct spacemit_i2c_dev *i2c = devid;
> +	u32 status, val;
> +
> +	status = readl(i2c->base + ISR);
> +	if (!status)
> +		return IRQ_HANDLED;
> +
> +	i2c->status = status;
> +
> +	i2c->err = status & (SR_BED | SR_RXOV | SR_ALD);
> +
> +	spacemit_i2c_clear_int_status(i2c, status);
> +
> +	if (unlikely(i2c->err))
> +		goto err_out;
> +
> +	val = readl(i2c->base + ICR);
> +
> +	val &= ~(CR_TB | CR_ACKNAK | CR_STOP | CR_START);
> +	writel(val, i2c->base + ICR);
> +
> +	switch (i2c->state) {
> +	case STATE_START:
> +		spacemit_i2c_handle_start(i2c);
> +		break;
> +	case STATE_READ:
> +		spacemit_i2c_handle_read(i2c);
> +		break;
> +	case STATE_WRITE:
> +		spacemit_i2c_handle_write(i2c);
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	if (i2c->state != STATE_IDLE) {
> +		if (spacemit_i2c_is_last_msg(i2c)) {
> +			/* trigger next byte with stop */
> +			spacemit_i2c_stop(i2c);
> +		} else {
> +			/* trigger next byte */
> +			val |= CR_ALDIE | CR_TB;
> +			writel(val, i2c->base + ICR);
> +		}
> +	}
> +
> +err_out:
> +	spacemit_i2c_err_check(i2c);
> +	return IRQ_HANDLED;
> +}
> +
> +static void spacemit_i2c_calc_timeout(struct spacemit_i2c_dev *i2c)
> +{
> +	unsigned long timeout;
> +	int idx = 0, cnt = 0, freq;
> +
> +	while (idx < i2c->msg_num) {
> +		cnt += (i2c->msgs + idx)->len + 1;
> +		idx++;
> +	}
> +
> +	freq = I2C_FAST_MODE_FREQ;
so this will set frequency to fast mode (400K), this contradict with PATCH[1/2] which
says default clock-frequency is 100000, either you need to change the code? or
update the dt-binding?

> +	/*
> +	 * multiply by 9 because each byte in I2C transmission requires
> +	 * 9 clock cycles: 8 bits of data plus 1 ACK/NACK bit.
> +	 */
> +	timeout = cnt * 9 * USEC_PER_SEC / freq;
> +
> +	i2c->adapt.timeout = usecs_to_jiffies(timeout + USEC_PER_SEC / 2) / i2c->msg_num;
> +}
> +
> +static inline int spacemit_i2c_xfer_core(struct spacemit_i2c_dev *i2c)
drop inline? IMO, it isn't worth here for long function

> +{
> +	int ret = 0;
no need to initilize to 0
> +
> +	spacemit_i2c_reset(i2c);
> +
> +	spacemit_i2c_calc_timeout(i2c);
> +
> +	spacemit_i2c_init(i2c);
> +
> +	spacemit_i2c_enable(i2c);
> +	enable_irq(i2c->irq);
> +
> +	/* i2c wait for bus busy */
> +	ret = spacemit_i2c_recover_bus_busy(i2c);
> +	if (unlikely(ret))
> +		return ret;
> +
> +	ret = spacemit_i2c_xfer_msg(i2c);
> +	if (unlikely(ret < 0)) {
> +		dev_dbg(i2c->dev, "i2c transfer error\n");
> +		/* timeout error should not be overridden, and the transfer
> +		 * error will be confirmed by err handle function latter,
> +		 * the reset should be invalid argument error.
> +		 */
> +		if (ret != -ETIMEDOUT)
> +			ret = -EINVAL;
> +	}
> +
> +	return ret;
> +}
> +
> +static int
> +spacemit_i2c_xfer(struct i2c_adapter *adapt, struct i2c_msg msgs[], int num)
no need to wrap the line, it makes the code a little bit weird..

current policy increase to 100characters, the old 80-column is not enforced
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bdc48fa11e46f867ea4d75fa59ee87a7f48be144

> +{
> +	struct spacemit_i2c_dev *i2c = i2c_get_adapdata(adapt);
> +	int ret;
> +
> +	i2c->msgs = msgs;
> +	i2c->msg_num = num;
> +
> +	ret = spacemit_i2c_xfer_core(i2c);
> +	if (likely(!ret))
> +		spacemit_i2c_check_bus_release(i2c);
> +
> +	disable_irq(i2c->irq);
> +
> +	spacemit_i2c_disable(i2c);
> +
> +	if (unlikely((ret == -ETIMEDOUT || ret == -EAGAIN)))
> +		dev_alert(i2c->dev, "i2c transfer failed, ret %d err 0x%x\n", ret, i2c->err);
> +
> +	return ret < 0 ? ret : num;
> +}
> +
> +static u32 spacemit_i2c_func(struct i2c_adapter *adap)
> +{
> +	return I2C_FUNC_I2C | (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
> +}
> +
> +static const struct i2c_algorithm spacemit_i2c_algo = {
> +	.xfer = spacemit_i2c_xfer,
> +	.functionality = spacemit_i2c_func,
> +};
> +
> +static int spacemit_i2c_probe(struct platform_device *pdev)
> +{
> +	struct spacemit_i2c_dev *i2c;
> +	struct device_node *of_node = pdev->dev.of_node;
> +	struct clk *clk;
> +	int ret = 0;
> +
> +	i2c = devm_kzalloc(&pdev->dev, sizeof(*i2c), GFP_KERNEL);
> +	if (!i2c)
> +		return -ENOMEM;
> +
> +	i2c->dev = &pdev->dev;
> +
> +	i2c->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(i2c->base))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(i2c->base), "failed to do ioremap");
> +
> +	i2c->irq = platform_get_irq(pdev, 0);
> +	if (i2c->irq < 0)
> +		return dev_err_probe(&pdev->dev, i2c->irq, "failed to get irq resource");
> +
> +	ret = devm_request_irq(i2c->dev, i2c->irq, spacemit_i2c_irq_handler,
> +			       IRQF_NO_SUSPEND | IRQF_ONESHOT, dev_name(i2c->dev), i2c);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret, "failed to request irq");
> +
> +	disable_irq(i2c->irq);
> +
> +	clk = devm_clk_get_enabled(&pdev->dev, NULL);
> +	if (IS_ERR(clk))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(clk), "failed to enable clock");
> +
I'd suggest also to handle pin request here, since pinctrl driver is merged

https://lore.kernel.org/all/CACRpkdYnaJsKKfcdhHeMGTTp86M+wNODzZx2e=OYbxQ4Jc4Rjw@mail.gmail.com/

> +	i2c_set_adapdata(&i2c->adapt, i2c);
> +	i2c->adapt.owner = THIS_MODULE;
> +	i2c->adapt.algo = &spacemit_i2c_algo;
> +	i2c->adapt.dev.parent = i2c->dev;
> +	i2c->adapt.nr = pdev->id;
> +
> +	i2c->adapt.dev.of_node = of_node;
> +	i2c->adapt.algo_data = i2c;
> +
> +	strscpy(i2c->adapt.name, "spacemit-i2c-adapter", sizeof(i2c->adapt.name));
> +
> +	init_completion(&i2c->complete);
> +
> +	ret = i2c_add_numbered_adapter(&i2c->adapt);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret, "failed to add i2c adapter");
> +
> +	platform_set_drvdata(pdev, i2c);
> +
> +	return 0;
> +}
> +
> +static void spacemit_i2c_remove(struct platform_device *pdev)
> +{
> +	struct spacemit_i2c_dev *i2c = platform_get_drvdata(pdev);
> +
> +	i2c_del_adapter(&i2c->adapt);
> +}
> +
> +static const struct of_device_id spacemit_i2c_of_match[] = {
> +	{ .compatible = "spacemit,k1-i2c", },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, spacemit_i2c_of_match);
> +
> +static struct platform_driver spacemit_i2c_driver = {
> +	.probe = spacemit_i2c_probe,
> +	.remove = spacemit_i2c_remove,
> +	.driver = {
> +		.name = "i2c-k1",
> +		.of_match_table = spacemit_i2c_of_match,
> +	},
> +};
> +module_platform_driver(spacemit_i2c_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("I2C bus driver for SpacemiT K1 SoC");
> 
> -- 
> 2.34.1
>