[PATCH v3] i2c: imx: honour I2C_M_IGNORE_NAK
Haobin Jiang
lemonoutput at foxmail.com
Tue Sep 8 09:01:45 PDT 2026
I2C_M_IGNORE_NAK is removed from the flags rejected by
i2c_imx_check_msgs(), so the flag is honoured as documented. I2C_M_STOP
stays unhandled to preserve existing behaviour and backward
compatibility. I2C_M_NO_RD_ACK stays rejected.
This change is meant to apply on top of the I2C_M_REV_DIR_ADDR and
I2C_M_NOSTART series [1], which is not yet merged.
Tested on an ALIENTEK i.MX6ULL mini board (v6.6.44, equivalent
backport) with a logic analyzer: with the flag, a 3-byte write to an
unpopulated address clocks out every byte (each NAK'd) and returns 0;
without the flag it aborts with -ENXIO after the address byte. A
4-byte read with the flag completes and returns 0 as well. Waveforms
and test logs: https://github.com/JHB11Hinson/i2c-imx-ignore-nak-test
Note: part of the code was generated with the assistance
of a generative AI tool (GLM 5.3) from the author's description of
the problem, then reviewed and verified by the author.
Link: https://lore.kernel.org/linux-i2c/20260812-for-upstream-i2c-imx-lx2160-reverse-v2-1-f1343714c5a9@free.fr/ # [1]
Signed-off-by: Haobin Jiang <lemonoutput at foxmail.com>
---
v1 -> v2:
- Honour I2C_M_IGNORE_NAK on the read path as well, mirroring
i2c-img-scb, instead of silently dropping the flag there.
- Force the PIO path for every message with I2C_M_IGNORE_NAK:
a NAK'd byte does not generate a further DMA request, so a
DMA write to a deliberately-NAKing target would stall until
DMA_TIMEOUT.
- Reject I2C_M_NO_RD_ACK instead of advertising blanket support
and silently ignoring it. I2C_M_STOP is not rejected: the
controller already emits a STOP after the final message, and
rejecting it would break the ov2659 camera on imx6qdl-ds.
v2 -> v3:
- Rebase on top of the I2C_M_REV_DIR_ADDR and I2C_M_NOSTART
series; the flag rejection moved to i2c_imx_check_msgs().
I2C_M_IGNORE_NAK is now honoured and I2C_M_STOP stays
unhandled, preserving the ov2659/SCCB use case and backward
compatibility as agreed during review.
- Keep the DMA write path checking ACK with ignore_nak=false,
as suggested during review; messages carrying
I2C_M_IGNORE_NAK are forced onto the PIO path.
- Fix double spaces after periods in the changelog and comments.
- State the use of a generative AI tool in the changelog.
- Test on an ALIENTEK i.MX6ULL mini board (v6.6.44, equivalent
backport); results linked in the commit message.
drivers/i2c/busses/i2c-imx.c | 31 ++++++++++++++++++++++---------
1 file changed, 22 insertions(+), 9 deletions(-)
diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index ab6794bf3ea5..9cd1fa0f4021 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -612,9 +612,12 @@ static int i2c_imx_trx_complete(struct imx_i2c_struct *i2c_imx, bool atomic)
return 0;
}
-static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx)
+static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx, bool ignore_nak)
{
if (imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR) & I2SR_RXAK) {
+ if (ignore_nak)
+ return 0;
+
dev_dbg(&i2c_imx->adapter.dev, "<%s> No ACK\n", __func__);
return -ENXIO; /* No ACK */
}
@@ -968,11 +971,15 @@ static int i2c_imx_unreg_slave(struct i2c_client *client)
return ret;
}
-static inline int i2c_imx_isr_acked(struct imx_i2c_struct *i2c_imx)
+static inline int i2c_imx_isr_acked(struct imx_i2c_struct *i2c_imx,
+ bool ignore_nak)
{
i2c_imx->isr_result = 0;
if (imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR) & I2SR_RXAK) {
+ if (ignore_nak)
+ return 0;
+
i2c_imx->state = IMX_I2C_STATE_FAILED;
i2c_imx->isr_result = -ENXIO;
wake_up(&i2c_imx->queue);
@@ -985,7 +992,7 @@ static inline int i2c_imx_isr_write(struct imx_i2c_struct *i2c_imx)
{
int result;
- result = i2c_imx_isr_acked(i2c_imx);
+ result = i2c_imx_isr_acked(i2c_imx, i2c_imx->msg->flags & I2C_M_IGNORE_NAK);
if (result)
return result;
@@ -1014,7 +1021,7 @@ static inline int i2c_imx_isr_read(struct imx_i2c_struct *i2c_imx)
{
int result;
- result = i2c_imx_isr_acked(i2c_imx);
+ result = i2c_imx_isr_acked(i2c_imx, i2c_imx->msg->flags & I2C_M_IGNORE_NAK);
if (result)
return result;
@@ -1229,7 +1236,8 @@ static int i2c_imx_dma_write(struct imx_i2c_struct *i2c_imx,
if (result)
return result;
- return i2c_imx_acked(i2c_imx);
+ /* I2C_M_IGNORE_NAK messages never take the DMA path. */
+ return i2c_imx_acked(i2c_imx, false);
}
static int i2c_imx_prepare_read(struct imx_i2c_struct *i2c_imx,
@@ -1248,7 +1256,7 @@ static int i2c_imx_prepare_read(struct imx_i2c_struct *i2c_imx,
result = i2c_imx_trx_complete(i2c_imx, !use_dma);
if (result)
return result;
- result = i2c_imx_acked(i2c_imx);
+ result = i2c_imx_acked(i2c_imx, msgs->flags & I2C_M_IGNORE_NAK);
if (result)
return result;
}
@@ -1381,7 +1389,7 @@ static int i2c_imx_atomic_write(struct imx_i2c_struct *i2c_imx,
result = i2c_imx_trx_complete(i2c_imx, true);
if (result)
return result;
- result = i2c_imx_acked(i2c_imx);
+ result = i2c_imx_acked(i2c_imx, msgs->flags & I2C_M_IGNORE_NAK);
if (result)
return result;
}
@@ -1396,7 +1404,7 @@ static int i2c_imx_atomic_write(struct imx_i2c_struct *i2c_imx,
result = i2c_imx_trx_complete(i2c_imx, true);
if (result)
return result;
- result = i2c_imx_acked(i2c_imx);
+ result = i2c_imx_acked(i2c_imx, msgs->flags & I2C_M_IGNORE_NAK);
if (result)
return result;
}
@@ -1580,8 +1588,9 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs,
return ret;
}
+ /* I2C_M_STOP is the controller's native behaviour; don't reject it. */
#define I2C_IMX_UNSUPPORTED_PROTOCOL_MANGLING_FLAGS \
- (I2C_M_IGNORE_NAK | I2C_M_NO_RD_ACK | I2C_M_STOP)
+ I2C_M_NO_RD_ACK
static int i2c_imx_check_msgs(struct i2c_msg *msgs, int num)
{
@@ -1675,6 +1684,10 @@ static int i2c_imx_xfer_common(struct i2c_adapter *adapter,
use_dma = i2c_imx->dma && msgs[i].len >= DMA_THRESHOLD &&
msgs[i].flags & I2C_M_DMA_SAFE &&
!(msgs[i].flags & I2C_M_NOSTART);
+
+ /* A NAK'd byte may not generate a further DMA request. */
+ if (msgs[i].flags & I2C_M_IGNORE_NAK)
+ use_dma = false;
if (msgs[i].flags & I2C_M_RD) {
int block_data = msgs->flags & I2C_M_RECV_LEN;
base-commit: 04e9bf1648f846976b543e91c1838a712433772a
prerequisite-patch-id: 24876ef6d4dc440b8d8080e65d369b2b37709b0b
--
2.34.1
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