i2c: imx: fix emulated smbus block read

JIRA: https://issues.redhat.com/browse/RHEL-116101

commit a5d0b9e
Author: Lukasz Kucharczyk <lukasz.kucharczyk@leica-geosystems.com>
Date:   Tue May 20 14:22:52 2025 +0200

    i2c: imx: fix emulated smbus block read

    Acknowledge the byte count submitted by the target.
    When I2C_SMBUS_BLOCK_DATA read operation is executed by
    i2c_smbus_xfer_emulated(), the length of the second (read) message is set
    to 1. Length of the block is supposed to be obtained from the target by the
    underlying bus driver.
    The i2c_imx_isr_read() function should emit the acknowledge on i2c bus
    after reading the first byte (i.e., byte count) while processing such
    message (as defined in Section 6.5.7 of System Management Bus
    Specification [1]). Without this acknowledge, the target does not submit
    subsequent bytes and the controller only reads 0xff's.

    In addition, store the length of block data obtained from the target in
    the buffer provided by i2c_smbus_xfer_emulated() - otherwise the first
    byte of actual data is erroneously interpreted as length of the data
    block.

    [1] https://smbus.org/specs/SMBus_3_3_20240512.pdf

    Fixes: 5f5c2d4 ("i2c: imx: prevent rescheduling in non dma mode")
    Signed-off-by: Lukasz Kucharczyk <lukasz.kucharczyk@leica-geosystems.com>
    Cc: <stable@vger.kernel.org> # v6.13+
    Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
    Reviewed-by: Stefan Eichenberger <eichest@gmail.com>
    Reviewed-by: Carlos Song <carlos.song@nxp.com>
    Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
    Link: https://lore.kernel.org/r/20250520122252.1475403-1-lukasz.kucharczyk@leica-geosystems.com

Signed-off-by: Jared Kangas <jkangas@redhat.com>

Author: rh-jkangas

drivers/i2c/busses/i2c-imx.c

@@ -1008,7 +1008,7 @@ static inline int i2c_imx_isr_read(struct imx_i2c_struct *i2c_imx)
 	/* setup bus to read data */
 	temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
 	temp &= ~I2CR_MTX;
-	if (i2c_imx->msg->len - 1)
+	if ((i2c_imx->msg->len - 1) || (i2c_imx->msg->flags & I2C_M_RECV_LEN))
 		temp &= ~I2CR_TXAK;
 
 	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
@@ -1063,6 +1063,7 @@ static inline void i2c_imx_isr_read_block_data_len(struct imx_i2c_struct *i2c_im
 		wake_up(&i2c_imx->queue);
 	}
 	i2c_imx->msg->len += len;
+	i2c_imx->msg->buf[i2c_imx->msg_buf_idx++] = len;
 }
 
 static irqreturn_t i2c_imx_master_isr(struct imx_i2c_struct *i2c_imx, unsigned int status)