[PATCH] i2c: iproc: reset bus after timeout if START_BUSY is stuck

[Jonas Gorski]

If a transaction times out, the START_BUSY signal may have gotten stuck,
and subsequent transactaction attempts will fail as the bus is still
considered busy.

To work around this, check if the START_BUSY bit is still asserted, and
reset the controller in case it is.

This is also done by the alternative, non-upstream iproc-smbus driver
implementation [1].

Works around situations like:

    bcm-iproc-2c 1803b000.i2c: transaction timed out
    bcm-iproc-2c 1803b000.i2c: bus is busy
    bcm-iproc-2c 1803b000.i2c: bus is busy
    bcm-iproc-2c 1803b000.i2c: bus is busy
    bcm-iproc-2c 1803b000.i2c: bus is busy
    bcm-iproc-2c 1803b000.i2c: bus is busy
    ...

where the bus never recovers after a timeout.

[1] https://github.com/opencomputeproject/onie/blob/master/patches/kernel/3.2.69/driver-iproc-smbus.patch

Fixes: e6e5dd3566e0 ("i2c: iproc: Add Broadcom iProc I2C Driver")
Signed-off-by: Jonas Gorski <jonas.gorski at bisdn.de>
---
The iproc-smbus driver does some additional checks/mitigations, but
since my I2C understanding is only very rudimentary, I didn't add them,
also the reset was enough to fix the issue I was seeing.

I was a bit conflicted about the Fixes tag, but since it fixes/work
around misbehaviour seen I decided to add one.

The issue was happening only in production, and only once per boot (so
far), but with 100% probability within a few hours.

 drivers/i2c/busses/i2c-bcm-iproc.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/i2c/busses/i2c-bcm-iproc.c b/drivers/i2c/busses/i2c-bcm-iproc.c
index 05c80680dff4..69f9c199fa3b 100644
--- a/drivers/i2c/busses/i2c-bcm-iproc.c
+++ b/drivers/i2c/busses/i2c-bcm-iproc.c
@@ -796,6 +796,15 @@ static int bcm_iproc_i2c_xfer_wait(struct bcm_iproc_i2c_dev *iproc_i2c,
 	if (!time_left && !iproc_i2c->xfer_is_done) {
 		dev_err(iproc_i2c->device, "transaction timed out\n");
 
+		/* check if START_BUSY did not clear */
+		if (!!(iproc_i2c_rd_reg(iproc_i2c, M_CMD_OFFSET) &
+		       BIT(M_CMD_START_BUSY_SHIFT))) {
+			/* re-initialize i2c for recovery */
+			bcm_iproc_i2c_enable_disable(iproc_i2c, false);
+			bcm_iproc_i2c_init(iproc_i2c);
+			bcm_iproc_i2c_enable_disable(iproc_i2c, true);
+		}
+
 		/* flush both TX/RX FIFOs */
 		val = BIT(M_FIFO_RX_FLUSH_SHIFT) | BIT(M_FIFO_TX_FLUSH_SHIFT);
 		iproc_i2c_wr_reg(iproc_i2c, M_FIFO_CTRL_OFFSET, val);
-- 
2.42.0


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