i2c: spacemit: remove stop function to avoid bus error

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>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
index ee08811f4087c8e709d25dd314854ed643cc5a47..84f132d0504dc992f2f961253b011b86afcc2bbc 100644 (file)
--- 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: