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

From: Adrian Hunter <adrian.hunter@intel.com>
To: alexandre.belloni@bootlin.com
Cc: Frank.Li@nxp.com, Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Aniket <aniketmaurya@google.com>,
	linux-i3c@lists.infradead.org
Subject: [PATCH 01/17] i3c: mipi-i3c-hci: Reset RING_OPERATION1 fields during init
Date: Fri, 19 Dec 2025 16:45:18 +0200	[thread overview]
Message-ID: <20251219144534.84391-2-adrian.hunter@intel.com> (raw)
In-Reply-To: <20251219144534.84391-1-adrian.hunter@intel.com>

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


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