[PATCH v2 2/6] i2c: spacemit: remove stop function to avoid bus error

Troy Mitchell
2025-09-25T02:04:24Z

Previously, STOP handling was split into two separate steps:
1) clear TB/STOP/START/ACK bits
2) issue STOP by calling spacemit_i2c_stop()

This left a small window where the control register was updated
twice, which can confuse the controller. While this race has not
been observed with interrupt-driven transfers, it reliably causes
bus errors in PIO mode.

Inline the STOP sequence into the IRQ handler and ensure that
control register bits are updated atomically in a single writel().

Fixes: 5ea558473fa31 ("i2c: spacemit: add support for SpacemiT K1 SoC")
Signed-off-by: Troy Mitchell <troy.mitchell@linux.spacemit.com>
---
drivers/i2c/busses/i2c-k1.c | 26 +++++++-------------------
1 file changed, 7 insertions(+), 19 deletions(-)

diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
index ee08811f4087c8e709d25dd314854ed643cc5a47..84f132d0504dc992f2f961253b011b86afcc2bbc 100644
--- a/drivers/i2c/busses/i2c-k1.c
+++ b/drivers/i2c/busses/i2c-k1.c
@@ -267,19 +267,6 @@ static void spacemit_i2c_start(struct spacemit_i2c_dev *i2c)
writel(val, i2c->base + SPACEMIT_ICR);
}

-static void spacemit_i2c_stop(struct spacemit_i2c_dev *i2c)
-{
- u32 val;
-
- val = readl(i2c->base + SPACEMIT_ICR);
- val |= SPACEMIT_CR_STOP | SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
-
- if (i2c->read)
- val |= SPACEMIT_CR_ACKNAK;
-
- writel(val, i2c->base + SPACEMIT_ICR);
-}
-
static int spacemit_i2c_xfer_msg(struct spacemit_i2c_dev *i2c)
{
unsigned long time_left;
@@ -412,7 +399,6 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)

val = readl(i2c->base + SPACEMIT_ICR);
val &= ~(SPACEMIT_CR_TB | SPACEMIT_CR_ACKNAK | SPACEMIT_CR_STOP | SPACEMIT_CR_START);
- writel(val, i2c->base + SPACEMIT_ICR);

switch (i2c->state) {
case SPACEMIT_STATE_START:
@@ -429,14 +415,16 @@ static irqreturn_t spacemit_i2c_irq_handler(int irq, void *devid)
}

if (i2c->state != SPACEMIT_STATE_IDLE) {
+ val |= SPACEMIT_CR_TB | SPACEMIT_CR_ALDIE;
+
if (spacemit_i2c_is_last_msg(i2c)) {
/* trigger next byte with stop */
- spacemit_i2c_stop(i2c);
- } else {
- /* trigger next byte */
- val |= SPACEMIT_CR_ALDIE | SPACEMIT_CR_TB;
- writel(val, i2c->base + SPACEMIT_ICR);
+ val |= SPACEMIT_CR_STOP;
+
+ if (i2c->read)
+ val |= SPACEMIT_CR_ACKNAK;
}
+ writel(val, i2c->base + SPACEMIT_ICR);
}

err_out:

--
2.51.0