RE: [PATCH v2] i2c: imx: add I2C_M_REV_DIR_ADDR and I2C_M_NOSTART

Hi,

LGTM.

Acked-by: Carlos Song <[email protected]>


NXP Confidential
> -----Original Message-----
> From: Vincent Jardin via B4 Relay <[email protected]>
> Sent: Thursday, August 13, 2026 3:16 AM
> To: Oleksij Rempel <[email protected]>; Pengutronix Kernel Team
> <[email protected]>; Andi Shyti <[email protected]>; Frank Li
> <[email protected]>; Sascha Hauer <[email protected]>; Fabio
> Estevam <[email protected]>
> Cc: [email protected]; [email protected];
> [email protected]; [email protected]; Vincent
> Jardin <[email protected]>
> Subject: [PATCH v2] i2c: imx: add I2C_M_REV_DIR_ADDR and
> I2C_M_NOSTART
>
> From: Vincent Jardin <[email protected]>
>
> The Realtek RTL8366SE SMI read frame per:
>
>   S Addr Rd [A] reg[7:0] [A] reg[15:8] [A] [data[7:0]] A [data[15:8]] NA P
>
> Linux support it using I2C_M_REV_DIR_ADDR on a write message that inverts
> the transmitted R/W bit, and I2C_M_NOSTART on the following read message
> that continues the frame without re-addressing.
>
> This NXP i2c-imx is missing such support, so on an LX2160A the Realtek switch
> could not be used.
>
> Signed-off-by: Vincent Jardin <[email protected]>
> ---
> Follow the logics from i2c-algo-bit and i2c-s3c2410 (addr ^= 1).
>
> Documentation/i2c/i2c-protocol.rst says I2C_M_NOSTART "may also be used
> between direction changes by some rare devices"; the RTL8366SE is one of
> such device !
>
> - The NOSTART read turns the bus around without waiting for a completion,
>   because the controller stretches SCL after the previous byte and the
>   frame is therefore still open. That is what lets i2c_imx_read() enter
>   the state the ISR would otherwise have moved to.
>
> - I2C_FUNC_PROTOCOL_MANGLING also covers I2C_M_IGNORE_NAK,
>   I2C_M_NO_RD_ACK and I2C_M_STOP, which this driver does not
> implement.
>   They are rejected with -EOPNOTSUPP rather than advertised and silently
>   ignored. I2C_M_NOSTART on the first message is rejected as well.
> ---
> Changes in v2:
> - message validation with i2c_imx_check_msgs() (Carlos Song)
>   No functional change
> - Link to v1:
> https://lore.kernel.org/r/20260807-for-upstream-i2c-imx-lx2160-reverse-v1-
> [email protected]
> ---
>  drivers/i2c/busses/i2c-imx.c | 153
> ++++++++++++++++++++++++++++++++-----------
>  1 file changed, 113 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c index
> 9477d814fde9..7dc9c43673ee 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -1000,16 +1000,10 @@ static inline int i2c_imx_isr_write(struct
> imx_i2c_struct *i2c_imx)
>       return 1;
>  }
>
> -static inline int i2c_imx_isr_read(struct imx_i2c_struct *i2c_imx)
> +static inline void i2c_imx_setup_read(struct imx_i2c_struct *i2c_imx)
>  {
> -     int result;
>       unsigned int temp;
>
> -     result = i2c_imx_isr_acked(i2c_imx);
> -     if (result)
> -             return result;
> -
> -     /* setup bus to read data */
>       temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
>       temp &= ~I2CR_MTX;
>       if ((i2c_imx->msg->len - 1) || (i2c_imx->msg->flags & I2C_M_RECV_LEN))
> @@ -1017,6 +1011,18 @@ static inline int i2c_imx_isr_read(struct
> imx_i2c_struct *i2c_imx)
>
>       imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
>       imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR); /* dummy read */
> +}
> +
> +static inline int i2c_imx_isr_read(struct imx_i2c_struct *i2c_imx) {
> +     int result;
> +
> +     result = i2c_imx_isr_acked(i2c_imx);
> +     if (result)
> +             return result;
> +
> +     /* setup bus to read data */
> +     i2c_imx_setup_read(i2c_imx);
>
>       return 0;
>  }
> @@ -1172,6 +1178,16 @@ static irqreturn_t i2c_imx_isr(int irq, void *dev_id)
>       return i2c_imx_master_isr(i2c_imx, status);  }
>
> +static u8 i2c_imx_addr_byte(struct i2c_msg *msg) {
> +     u8 addr = i2c_8bit_addr_from_msg(msg);
> +
> +     if (msg->flags & I2C_M_REV_DIR_ADDR)
> +             addr ^= 1;
> +
> +     return addr;
> +}
> +
>  static int i2c_imx_dma_write(struct imx_i2c_struct *i2c_imx,
>                                       struct i2c_msg *msgs)
>  {
> @@ -1200,7 +1216,7 @@ static int i2c_imx_dma_write(struct imx_i2c_struct
> *i2c_imx,
>        * Write slave address.
>        * The first byte must be transmitted by the CPU.
>        */
> -     imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx,
> IMX_I2C_I2DR);
> +     imx_i2c_write_reg(i2c_imx_addr_byte(msgs), i2c_imx, IMX_I2C_I2DR);
>       time_left = wait_for_completion_timeout(
>                               &i2c_imx->dma->cmd_complete,
>                               msecs_to_jiffies(DMA_TIMEOUT));
> @@ -1242,14 +1258,20 @@ static int i2c_imx_prepare_read(struct
> imx_i2c_struct *i2c_imx,
>       int result;
>       unsigned int temp = 0;
>
> -     /* write slave address */
> -     imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx,
> IMX_I2C_I2DR);
> -     result = i2c_imx_trx_complete(i2c_imx, !use_dma);
> -     if (result)
> -             return result;
> -     result = i2c_imx_acked(i2c_imx);
> -     if (result)
> -             return result;
> +     /*
> +      * I2C_M_NOSTART continues a frame that is already open, so there is
> +      * no address phase: go straight to turning the bus around.
> +      */
> +     if (!(msgs->flags & I2C_M_NOSTART)) {
> +             /* write slave address */
> +             imx_i2c_write_reg(i2c_imx_addr_byte(msgs), i2c_imx,
> IMX_I2C_I2DR);
> +             result = i2c_imx_trx_complete(i2c_imx, !use_dma);
> +             if (result)
> +                     return result;
> +             result = i2c_imx_acked(i2c_imx);
> +             if (result)
> +                     return result;
> +     }
>
>       dev_dbg(&i2c_imx->adapter.dev, "<%s> setup bus\n", __func__);
>
> @@ -1371,16 +1393,18 @@ static int i2c_imx_atomic_write(struct
> imx_i2c_struct *i2c_imx,
>       int i, result;
>
>       dev_dbg(&i2c_imx->adapter.dev, "<%s> write slave address:
> addr=0x%x\n",
> -             __func__, i2c_8bit_addr_from_msg(msgs));
> +             __func__, i2c_imx_addr_byte(msgs));
>
> -     /* write slave address */
> -     imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx,
> IMX_I2C_I2DR);
> -     result = i2c_imx_trx_complete(i2c_imx, true);
> -     if (result)
> -             return result;
> -     result = i2c_imx_acked(i2c_imx);
> -     if (result)
> -             return result;
> +     if (!(msgs->flags & I2C_M_NOSTART)) {
> +             /* write slave address */
> +             imx_i2c_write_reg(i2c_imx_addr_byte(msgs), i2c_imx,
> IMX_I2C_I2DR);
> +             result = i2c_imx_trx_complete(i2c_imx, true);
> +             if (result)
> +                     return result;
> +             result = i2c_imx_acked(i2c_imx);
> +             if (result)
> +                     return result;
> +     }
>       dev_dbg(&i2c_imx->adapter.dev, "<%s> write data\n", __func__);
>
>       /* write data */
> @@ -1402,7 +1426,7 @@ static int i2c_imx_atomic_write(struct
> imx_i2c_struct *i2c_imx,  static int i2c_imx_write(struct imx_i2c_struct
> *i2c_imx, struct i2c_msg *msgs)  {
>       dev_dbg(&i2c_imx->adapter.dev, "<%s> write slave address:
> addr=0x%x\n",
> -             __func__, i2c_8bit_addr_from_msg(msgs));
> +             __func__, i2c_imx_addr_byte(msgs));
>
>       i2c_imx->state = IMX_I2C_STATE_WRITE;
>       i2c_imx->msg = msgs;
> @@ -1411,8 +1435,16 @@ static int i2c_imx_write(struct imx_i2c_struct
> *i2c_imx, struct i2c_msg *msgs)
>       /*
>        * By writing the device address we start the state machine in the ISR.
>        * The ISR will report when it is done or when it fails.
> +      *
> +      * I2C_M_NOSTART continues a frame that is already open and so has
> no
> +      * address byte: push the first data byte instead. That raises the same
> +      * interrupt and the ISR carries on from the second byte.
>        */
> -     imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx,
> IMX_I2C_I2DR);
> +     if (msgs->flags & I2C_M_NOSTART)
> +             imx_i2c_write_reg(msgs->buf[i2c_imx->msg_buf_idx++], i2c_imx,
> +                               IMX_I2C_I2DR);
> +     else
> +             imx_i2c_write_reg(i2c_imx_addr_byte(msgs), i2c_imx,
> IMX_I2C_I2DR);
>       wait_event_timeout(i2c_imx->queue,
>                          i2c_imx->state == IMX_I2C_STATE_DONE ||
>                          i2c_imx->state == IMX_I2C_STATE_FAILED, @@ -1529,22
> +1561,29 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct
> i2c_msg *msgs,
>
>       dev_dbg(&i2c_imx->adapter.dev,
>               "<%s> write slave address: addr=0x%x\n",
> -             __func__, i2c_8bit_addr_from_msg(msgs));
> +             __func__, i2c_imx_addr_byte(msgs));
>
>       i2c_imx->is_lastmsg = is_lastmsg;
>
> -     if (block_data)
> -             i2c_imx->state = IMX_I2C_STATE_READ_BLOCK_DATA;
> -     else
> -             i2c_imx->state = IMX_I2C_STATE_READ;
>       i2c_imx->msg = msgs;
>       i2c_imx->msg_buf_idx = 0;
>
> -     /*
> -      * By writing the device address we start the state machine in the ISR.
> -      * The ISR will report when it is done or when it fails.
> -      */
> -     imx_i2c_write_reg(i2c_8bit_addr_from_msg(msgs), i2c_imx,
> IMX_I2C_I2DR);
> +     if (msgs->flags & I2C_M_NOSTART) {
> +             i2c_imx->state = block_data ?
> IMX_I2C_STATE_READ_BLOCK_DATA_LEN
> +                                         : IMX_I2C_STATE_READ_CONTINUE;
> +             i2c_imx_setup_read(i2c_imx);
> +     } else {
> +             if (block_data)
> +                     i2c_imx->state = IMX_I2C_STATE_READ_BLOCK_DATA;
> +             else
> +                     i2c_imx->state = IMX_I2C_STATE_READ;
> +
> +             /*
> +              * By writing the device address we start the state machine in the
> ISR.
> +              * The ISR will report when it is done or when it fails.
> +              */
> +             imx_i2c_write_reg(i2c_imx_addr_byte(msgs), i2c_imx,
> IMX_I2C_I2DR);
> +     }
>       wait_event_timeout(i2c_imx->queue,
>                          i2c_imx->state == IMX_I2C_STATE_DONE ||
>                          i2c_imx->state == IMX_I2C_STATE_FAILED, @@ -1574,6
> +1613,33 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct
> i2c_msg *msgs,
>       return ret;
>  }
>
> +#define I2C_IMX_UNSUPPORTED_PROTOCOL_MANGLING_FLAGS \
> +     (I2C_M_IGNORE_NAK | I2C_M_NO_RD_ACK | I2C_M_STOP)
> +
> +static int i2c_imx_check_msgs(struct i2c_msg *msgs, int num) {
> +     int i;
> +
> +     for (i = 0; i < num; i++) {
> +             /* Reject rather than silently transfer */
> +             if (msgs[i].flags &
> I2C_IMX_UNSUPPORTED_PROTOCOL_MANGLING_FLAGS)
> +                     return -EOPNOTSUPP;
> +
> +             if (msgs[i].flags & I2C_M_NOSTART) {
> +                     /*
> +                      * NOSTART continues an already open frame. The first
> +                      * message has nothing to continue from,
> +                      * a 0 length continuation leaves the controller with
> +                      * no byte to clock.
> +                      */
> +                     if (i == 0 || msgs[i].len == 0)
> +                             return -EOPNOTSUPP;
> +             }
> +     }
> +
> +     return 0;
> +}
> +
>  static int i2c_imx_xfer_common(struct i2c_adapter *adapter,
>                              struct i2c_msg *msgs, int num, bool atomic)  { @@
> -1583,6 +1649,10 @@ static int i2c_imx_xfer_common(struct i2c_adapter
> *adapter,
>       struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
>       int use_dma = 0;
>
> +     result = i2c_imx_check_msgs(msgs, num);
> +     if (result)
> +             return result;
> +
>       /* Start I2C transfer */
>       result = i2c_imx_start(i2c_imx, atomic);
>       if (result) {
> @@ -1604,7 +1674,7 @@ static int i2c_imx_xfer_common(struct i2c_adapter
> *adapter,
>               if (i == num - 1)
>                       is_lastmsg = true;
>
> -             if (i) {
> +             if (i && !(msgs[i].flags & I2C_M_NOSTART)) {
>                       dev_dbg(&i2c_imx->adapter.dev,
>                               "<%s> repeated start\n", __func__);
>                       temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR); @@
> -1636,7 +1706,8 @@ static int i2c_imx_xfer_common(struct i2c_adapter
> *adapter,  #endif
>
>               use_dma = i2c_imx->dma && msgs[i].len >= DMA_THRESHOLD &&
> -                     msgs[i].flags & I2C_M_DMA_SAFE;
> +                     msgs[i].flags & I2C_M_DMA_SAFE &&
> +                     !(msgs[i].flags & I2C_M_NOSTART);
>               if (msgs[i].flags & I2C_M_RD) {
>                       int block_data = msgs->flags & I2C_M_RECV_LEN;
>
> @@ -1730,7 +1801,9 @@ static int i2c_imx_init_recovery_info(struct
> imx_i2c_struct *i2c_imx,  static u32 i2c_imx_func(struct i2c_adapter
> *adapter)  {
>       return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL
> -             | I2C_FUNC_SMBUS_READ_BLOCK_DATA;
> +             | I2C_FUNC_SMBUS_READ_BLOCK_DATA
> +             | I2C_FUNC_NOSTART
> +             | I2C_FUNC_PROTOCOL_MANGLING;
>  }
>
>  static const struct i2c_algorithm i2c_imx_algo = {
>
> ---
> base-commit: 3d6d817622b0a9721e3cc404df3469171582be13
> change-id: 20260807-for-upstream-i2c-imx-lx2160-reverse-7a94b9561188
>
> Best regards,
> --
> Vincent Jardin <[email protected]>
>
>