[PATCH v2] i2c: iproc: reset bus after timeout if START_BUSY is stuck

[Jonas Gorski <jonas.gorski@bisdn.de>]

If a transaction times out, the START_BUSY signal can stay up, and
subsequent transactaction attempts will fail as the bus is still
considered busy.

I can easily trigger this by attempting to read from an address with no
device, e.g. when running i2cdetect. After the first read times out, all
subsequent read attempts return busy.

To get to a working state again, the controller needs to be reset to
clear the START_BUSY signal. So check for START_BUSY still asserted on a
timeout, and do reset in case it is,

This is also done by the original 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@bisdn.de>
---
v1 -> v2:
* rebased on current master
* reworded the comment and the commit message, as I found I could
  trigger this intentionally

v1: https://lore.kernel.org/all/20230904090005.52622-1-jonas.gorski@bisdn.de/

 drivers/i2c/busses/i2c-bcm-iproc.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/i2c/busses/i2c-bcm-iproc.c b/drivers/i2c/busses/i2c-bcm-iproc.c
index b5629cffe99b..86ca4c2221c4 100644
--- a/drivers/i2c/busses/i2c-bcm-iproc.c
+++ b/drivers/i2c/busses/i2c-bcm-iproc.c
@@ -803,6 +803,17 @@ static int bcm_iproc_i2c_xfer_wait(struct bcm_iproc_i2c_dev *iproc_i2c,
 	}
 
 	if (!time_left && !iproc_i2c->xfer_is_done) {
+		/*
+		 * The controller may fail to clear START_BUSY after a timeout,
+		 * reset the controller to recover in that case.
+		 */
+		if (!!(iproc_i2c_rd_reg(iproc_i2c, M_CMD_OFFSET) &
+		       BIT(M_CMD_START_BUSY_SHIFT))) {
+			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);
-- 
2.55.0


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