i2c: imx: fix locked bus on SMBus block-read of 0 (IRQ)

SMBus 3.1 6.5.7 allows a Block Read byte count of 0, but the
interrupt-driven block-read state machine rejects it as -EPROTO. Worse,
it returns without a NACK+STOP: the next receive cycle has already
started, so the target keeps holding SDA and the bus stays stuck until a
power cycle of this i2c controller.

Accept count=0: NACK the in-flight dummy byte (TXAK) and set msg->len to
2 so i2c_imx_isr_read_continue() emits STOP via its normal last-byte
path. The dummy byte is discarded; block-read callers only consume
buf[0..count-1].

Reading I2DR has likewise already armed the next byte on the
count > I2C_SMBUS_BLOCK_MAX error path, so NACK it (TXAK) before aborting
with -EPROTO; otherwise the failing transfer's STOP cannot complete and
the bus stays held.

The atomic path regressed earlier (v3.16) and is fixed separately; this
patch covers only the v6.13 state-machine rework.

Fixes: 5f5c2d4579ca ("i2c: imx: prevent rescheduling in non dma mode")
Signed-off-by: Vincent Jardin <vjardin@free.fr>
Cc: <stable@vger.kernel.org> # v6.13+
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Carlos Song <carlos.song@nxp.com>
Reviewed-by: Stefan Eichenberger <eichest@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20260713-for-upstream-i2c-lx2160-fix-v1-v3-2-073ac9e103a5@free.fr

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index cfd1e63359e75c38970c6851aacb642a0626c17b..d5e6e2eca3b34da30dc7a54d8dcd09436ae754de 100644 (file)
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -1061,11 +1061,28 @@ static inline enum imx_i2c_state i2c_imx_isr_read_continue(struct imx_i2c_struct
 static inline void i2c_imx_isr_read_block_data_len(struct imx_i2c_struct *i2c_imx)
 {
        u8 len = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
+       unsigned int temp;
 
        if (len == 0 || len > I2C_SMBUS_BLOCK_MAX) {
+               /*
+                * SMBus 3.1 6.5.7: support count byte of 0.
+                * I2C_SMBUS_BLOCK_MAX case should not hold the SDA either.
+                * So NACK it (TXAK) to not hold the bus.
+                */
+               temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
+               temp |= I2CR_TXAK;
+               imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
+
+               if (len == 0) {
+                       i2c_imx->msg->buf[i2c_imx->msg_buf_idx++] = 0;
+                       i2c_imx->msg->len = 2;
+                       return;
+               }
+
                i2c_imx->isr_result = -EPROTO;
                i2c_imx->state = IMX_I2C_STATE_FAILED;
                wake_up(&i2c_imx->queue);
+               return;
        }
        i2c_imx->msg->len += len;
        i2c_imx->msg->buf[i2c_imx->msg_buf_idx++] = len;