[PATCH 01/17] i3c: mipi-i3c-hci: Reset RING_OPERATION1 fields during init

Adrian Hunter
2025-12-19T14:45:54Z

The MIPI I3C HCI specification does not define reset values for
RING_OPERATION1 fields, and some controllers (e.g., Intel) do not clear
them during a software reset. Ensure the ring pointers are explicitly
set to zero during bus initialization to avoid inconsistent state.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
drivers/i3c/master/mipi-i3c-hci/dma.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/i3c/master/mipi-i3c-hci/dma.c b/drivers/i3c/master/mipi-i3c-hci/dma.c
index 0f6bbe184e85..5515ed740ca4 100644
--- a/drivers/i3c/master/mipi-i3c-hci/dma.c
+++ b/drivers/i3c/master/mipi-i3c-hci/dma.c
@@ -340,6 +340,14 @@ static int hci_dma_init(struct i3c_hci *hci)
rh_reg_write(INTR_SIGNAL_ENABLE, regval);

ring_ready:
+ /*
+ * The MIPI I3C HCI specification does not document reset values for
+ * RING_OPERATION1 fields and some controllers (e.g. Intel controllers)
+ * do not reset the values, so ensure the ring pointers are set to zero
+ * here.
+ */
+ rh_reg_write(RING_OPERATION1, 0);
+
rh_reg_write(RING_CONTROL, RING_CTRL_ENABLE |
RING_CTRL_RUN_STOP);
}
--
2.51.0