[PATCH 6.18 032/752] i3c: mipi-i3c-hci: Reset RING_OPERATION1 fields during init

Sasha Levin
2026-02-28T17:48:36Z

From: Adrian Hunter <adrian.hunter@intel.com>

[ Upstream commit 78f63ae4a82db173f93adca462e63d11ba06b126 ]

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>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260113072702.16268-2-adrian.hunter@intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 c401a9425cdc5..951abfea5a6fd 100644
--- a/drivers/i3c/master/mipi-i3c-hci/dma.c
+++ b/drivers/i3c/master/mipi-i3c-hci/dma.c
@@ -342,6 +342,14 @@ 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