[PATCH v6] i2c: imx: honour I2C_M_IGNORE_NAK
From: Haobin Jiang
Date: Fri Nov 06 2026 - 04:26:06 EST
The driver rejects I2C_M_IGNORE_NAK with -EOPNOTSUPP, preventing
NAK-tolerant wake-token and SCCB transfers. Honour the flag in PIO
ACK checks and force flagged messages to PIO to avoid DMA stalls.
Restore acceptance of I2C_M_STOP for ov2659/SCCB compatibility [1],
without implementing STOP between messages.
Following Sashiko's report [2], reject flagged zero-length reads before
START with -EOPNOTSUPP to avoid an existing receive-path overrun.
Unflagged zero-length reads are unchanged.
Tested on ALIENTEK i.MX6ULL mini with this patch on f7813d226107,
using /dev/i2c-0 at 100 kHz and unpopulated address 0x60. The test
kernel reports 7.3.0-gf7813d226107-dirty (patch applied but not
committed). Logic analyzer CH0=SCL, CH1=SDA, sampled at 2 MHz.
On the same patched kernel, an unflagged 3-byte write returns -ENXIO
after the address NAK (9 clocks); with the flag it completes (36
clocks). A flagged 4-byte read returns ff ff ff ff (45 clocks), and a
flagged zero-length read returns -EOPNOTSUPP before START. Captures
and serial logs are in [3].
AI assistance: GLM 5.3 assisted with driver code from the author's
problem description; GPT-6.1Sol/Codex assisted with the test harness
from my test plan and polished the submission text. I have reviewed
the content.
Link: https://lore.kernel.org/linux-i2c/392c76a6-1ba5-4bc1-bfba-524025359042@xxxxxxxxxxx/ # [1]
Link: https://lore.kernel.org/imx/sashiko-outbox-187010@xxxxxxxxxx/ # [2]
Link: https://github.com/JHB11Hinson/i2c-imx-ignore-nak-test # [3]
Signed-off-by: Haobin Jiang <lemonoutput@xxxxxxxxxxx>
---
Changes in v6:
- Clarify the I2C_M_STOP comment; no functional change from v5.
- Rebase onto f7813d226107; the base driver is unchanged from
123cffeca4a3.
- Rework the commit message and review history following Carlos Song's
feedback, and document AI assistance.
- Retest on an ALIENTEK i.MX6ULL mini board on the new base.
- Link to v5: https://lore.kernel.org/linux-i2c/tencent_E6D69775D91AD9FE45C994B3755CB1452506@xxxxxx/
Changes in v5:
- Reject zero-length reads carrying I2C_M_IGNORE_NAK before START,
following Sashiko's review of v4.
- Link to v4: https://lore.kernel.org/linux-i2c/tencent_877C99956190215D644EB959DF1663542A0A@xxxxxx/
Changes in v4:
- Rebase onto i2c/i2c after Vincent Jardin's series was merged as
c2867bb0fa1d ("i2c: imx: add I2C_M_REV_DIR_ADDR and I2C_M_NOSTART").
- No functional change from v3.
- Link to v3: https://lore.kernel.org/linux-i2c/tencent_342A87BFCECA70C9982E68A79AAD878B6909@xxxxxx/
Changes in v3:
- Rebase onto Vincent Jardin's I2C_M_REV_DIR_ADDR and I2C_M_NOSTART
series; move flag checks to i2c_imx_check_msgs().
- Keep ignore_nak=false in the DMA write ACK check and leave
I2C_M_STOP unhandled for compatibility, as agreed during review.
- Fix spacing, disclose AI assistance and record v6.6.44 backport tests.
- Link to v2: https://lore.kernel.org/linux-i2c/tencent_E6A52FBBB25132C90B8E296FEB96E2C8CA07@xxxxxx/
Changes in v2:
- Honour I2C_M_IGNORE_NAK on reads and force flagged messages to PIO.
- Reject I2C_M_NO_RD_ACK; leave I2C_M_STOP unhandled for ov2659/SCCB.
- Link to v1: https://lore.kernel.org/linux-i2c/tencent_0D2E46A782AC418BC52A1BBF04CA1AC98E09@xxxxxx/
drivers/i2c/busses/i2c-imx.c | 37 +++++++++++++++++++++++++++---------
1 file changed, 28 insertions(+), 9 deletions(-)
diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index ccf08cd63..623503dda 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 */
}
@@ -971,11 +974,15 @@ 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);
@@ -988,7 +995,7 @@ 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;
@@ -1017,7 +1024,7 @@ 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;
@@ -1249,7 +1256,8 @@ 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,
@@ -1268,7 +1276,7 @@ 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;
}
@@ -1401,7 +1409,7 @@ 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;
}
@@ -1416,7 +1424,7 @@ 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;
}
@@ -1613,8 +1621,9 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs,
return ret;
}
+/* I2C_M_STOP is not implemented between messages; leave it unhandled. */
#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)
{
@@ -1625,6 +1634,12 @@ static int i2c_imx_check_msgs(struct i2c_msg *msgs, int num)
if (msgs[i].flags & I2C_IMX_UNSUPPORTED_PROTOCOL_MANGLING_FLAGS)
return -EOPNOTSUPP;
+ /* The receive path cannot handle zero-length reads. */
+ if ((msgs[i].flags & I2C_M_RD) &&
+ (msgs[i].flags & I2C_M_IGNORE_NAK) &&
+ msgs[i].len == 0)
+ return -EOPNOTSUPP;
+
if (msgs[i].flags & I2C_M_NOSTART) {
/*
* NOSTART continues an already open frame. The first
@@ -1712,6 +1727,10 @@ 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: f7813d226107618bac34f311bd613b658215f2c6
--
2.34.1