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

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SMBus 3.1 6.5.7 allows a Block Read byte count of 0, but the atomic
(polling) path 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 for
this i2c controller.

Reading I2DR to obtain the count likewise arms the next byte on the
count > I2C_SMBUS_BLOCK_MAX path, which also returned -EPROTO directly
and left the bus held.

Handle both: NACK the in-flight dummy byte (TXAK) and extend msgs->len so
the existing last-byte handling emits STOP; the dummy byte is discarded.
A count of 0 is a valid empty block read; a count above
I2C_SMBUS_BLOCK_MAX is still reported as -EPROTO, but only after the bus
has been released.

The interrupt-driven path has the same flaw from a later commit and is
fixed separately, as it carries a different Fixes: tag and stable range.

Fixes: 8e8782c715 ("i2c: imx: add SMBus block read support")
Signed-off-by: Vincent Jardin <vjardin@free.fr>
Cc: <stable@vger.kernel.org> # v3.16+
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-v3-1-073ac9e103a5@free.fr
This commit is contained in:
Vincent Jardin
2026-07-13 20:11:59 +02:00
committed by Andi Shyti
parent 627b6c94b8
commit cb2fc37857
1 changed files with 16 additions and 3 deletions
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19
drivers/i2c/busses/i2c-imx.c
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@@ -1415,6 +1415,7 @@ static int i2c_imx_atomic_read(struct imx_i2c_struct *i2c_imx,
int i, result;
unsigned int temp;
int block_data = msgs->flags & I2C_M_RECV_LEN;
int block_err = 0;
result = i2c_imx_prepare_read(i2c_imx, msgs, false);
if (result)
@@ -1436,8 +1437,20 @@ static int i2c_imx_atomic_read(struct imx_i2c_struct *i2c_imx,
*/
if ((!i) && block_data) {
len = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
if ((len == 0) || (len > I2C_SMBUS_BLOCK_MAX))
return -EPROTO;
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.
*/
if (len > I2C_SMBUS_BLOCK_MAX)
block_err = -EPROTO;
temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
temp |= I2CR_TXAK;
imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
msgs->buf[0] = 0;
msgs->len = 2;
continue;
}
dev_dbg(&i2c_imx->adapter.dev,
"<%s> read length: 0x%X\n",
__func__, len);
@@ -1485,7 +1498,7 @@ static int i2c_imx_atomic_read(struct imx_i2c_struct *i2c_imx,
"<%s> read byte: B%d=0x%X\n",
__func__, i, msgs->buf[i]);
}
return 0;
return block_err;
}
static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs,