FAILED: patch "[PATCH] i3c: mipi-i3c-hci: Fix race in DMA ring dequeue" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 1dca8aee80eea76d2aae21265de5dd64f6ba0f09
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026031728-preplan-unfunded-8460@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1dca8aee80eea76d2aae21265de5dd64f6ba0f09 Mon Sep 17 00:00:00 2001
From: Adrian Hunter <[email protected]>
Date: Fri, 6 Mar 2026 09:24:43 +0200
Subject: [PATCH] i3c: mipi-i3c-hci: Fix race in DMA ring dequeue

The HCI DMA dequeue path (hci_dma_dequeue_xfer()) may be invoked for multiple transfers that timeout around the same time. However, the function is not serialized and can race with itself.

When a timeout occurs, hci_dma_dequeue_xfer() stops the ring, processes incomplete transfers, and then restarts the ring. If another timeout triggers a parallel call into the same function, the two instances may interfere with each other - stopping or restarting the ring at unexpected times.

Add a mutex so that hci_dma_dequeue_xfer() is serialized with respect to itself.

index faf5eae2409f..061e84a5c412 100644
@@ -927,6 +927,7 @@ static int i3c_hci_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	spin_lock_init(&hci->lock);
+	mutex_init(&hci->control_mutex);
 
 	/*
 	 * Multi-bus instances share the same MMIO address range, but not

index 74b255ad6d0f..f7d411e5e11f 100644
@@ -547,6 +547,8 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
 	unsigned int i;
 	bool did_unqueue = false;
 
+	guard(mutex)(&hci->control_mutex);
+
 	/* stop the ring */
 	rh_reg_write(RING_CONTROL, RING_CTRL_ABORT);
 	if (wait_for_completion_timeout(&rh->op_done, HZ) == 0) {

index f1dd502c071f..9c63d80f7fc4 100644
@@ -51,6 +51,7 @@ struct i3c_hci {
 	void *io_data;
 	const struct hci_cmd_ops *cmd;
 	spinlock_t lock;
+	struct mutex control_mutex;
 	atomic_t next_cmd_tid;
 	bool irq_inactive;
 	u32 caps;