i3c: mipi-i3c-hci: Fix race between DMA ring dequeue and interrupt handler

The DMA ring bookkeeping in the MIPI I3C HCI driver is updated from two
contexts: the DMA ring dequeue path (hci_dma_dequeue_xfer()) and the
interrupt handler (hci_dma_xfer_done()).  Both modify the ring's
in-flight transfer state - specifically rh->src_xfers[] and
xfer->ring_entry - but without any serialization.  This allows the two
paths to race, potentially leading to inconsistent ring state.

Serialize access to the shared ring state by extending the existing
spinlock to cover the DMA dequeue path and the entire interrupt handler.
Since the core IRQ handler now holds this lock, remove the per-function
locking from the PIO and DMA sub-handlers.

Additionally, clear the completed entry in rh->src_xfers[] in
hci_dma_xfer_done() so it cannot be matched or completed again.

Finally, place the ring restart sequence under the same lock in
hci_dma_dequeue_xfer() to avoid concurrent enqueue or completion
operations while the ring state is being modified.

Fixes: 9ad9a52 ("i3c/master: introduce the mipi-i3c-hci driver")
Cc: stable@vger.kernel.org
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260306072451.11131-8-adrian.hunter@intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: ahunter6

drivers/i3c/master/mipi-i3c-hci/core.c

@@ -567,6 +567,8 @@ static irqreturn_t i3c_hci_irq_handler(int irq, void *dev_id)
 	irqreturn_t result = IRQ_NONE;
 	u32 val;
 
+	guard(spinlock)(&hci->lock);
+
 	/*
 	 * The IRQ can be shared, so the handler may be called when the IRQ is
 	 * due to a different device. That could happen when runtime suspended,

drivers/i3c/master/mipi-i3c-hci/dma.c

@@ -560,6 +560,8 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
 		WARN_ON(1);
 	}
 
+	spin_lock_irq(&hci->lock);
+
 	for (i = 0; i < n; i++) {
 		struct hci_xfer *xfer = xfer_list + i;
 		int idx = xfer->ring_entry;
@@ -593,6 +595,8 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
 	/* restart the ring */
 	rh_reg_write(RING_CONTROL, RING_CTRL_ENABLE);
 
+	spin_unlock_irq(&hci->lock);
+
 	return did_unqueue;
 }
 
@@ -618,6 +622,7 @@ static void hci_dma_xfer_done(struct i3c_hci *hci, struct hci_rh_data *rh)
 			dev_dbg(&hci->master.dev, "orphaned ring entry");
 		} else {
 			hci_dma_unmap_xfer(hci, xfer, 1);
+			rh->src_xfers[done_ptr] = NULL;
 			xfer->ring_entry = -1;
 			xfer->response = resp;
 			if (tid != xfer->cmd_tid) {
@@ -635,14 +640,11 @@ static void hci_dma_xfer_done(struct i3c_hci *hci, struct hci_rh_data *rh)
 		done_cnt += 1;
 	}
 
-	/* take care to update the software dequeue pointer atomically */
-	spin_lock(&hci->lock);
 	rh->xfer_space += done_cnt;
 	op1_val = rh_reg_read(RING_OPERATION1);
 	op1_val &= ~RING_OP1_CR_SW_DEQ_PTR;
 	op1_val |= FIELD_PREP(RING_OP1_CR_SW_DEQ_PTR, done_ptr);
 	rh_reg_write(RING_OPERATION1, op1_val);
-	spin_unlock(&hci->lock);
 }
 
 static int hci_dma_request_ibi(struct i3c_hci *hci, struct i3c_dev_desc *dev,
@@ -822,13 +824,10 @@ static void hci_dma_process_ibi(struct i3c_hci *hci, struct hci_rh_data *rh)
 	i3c_master_queue_ibi(dev, slot);
 
 done:
-	/* take care to update the ibi dequeue pointer atomically */
-	spin_lock(&hci->lock);
 	op1_val = rh_reg_read(RING_OPERATION1);
 	op1_val &= ~RING_OP1_IBI_DEQ_PTR;
 	op1_val |= FIELD_PREP(RING_OP1_IBI_DEQ_PTR, deq_ptr);
 	rh_reg_write(RING_OPERATION1, op1_val);
-	spin_unlock(&hci->lock);
 
 	/* update the chunk pointer */
 	rh->ibi_chunk_ptr += ibi_chunks;

drivers/i3c/master/mipi-i3c-hci/pio.c

@@ -1014,15 +1014,12 @@ static bool hci_pio_irq_handler(struct i3c_hci *hci)
 	struct hci_pio_data *pio = hci->io_data;
 	u32 status;
 
-	spin_lock(&hci->lock);
 	status = pio_reg_read(INTR_STATUS);
 	dev_dbg(&hci->master.dev, "PIO_INTR_STATUS %#x/%#x",
 		status, pio->enabled_irqs);
 	status &= pio->enabled_irqs | STAT_LATENCY_WARNINGS;
-	if (!status) {
-		spin_unlock(&hci->lock);
+	if (!status)
 		return false;
-	}
 
 	if (status & STAT_IBI_STATUS_THLD)
 		hci_pio_process_ibi(hci, pio);
@@ -1056,7 +1053,6 @@ static bool hci_pio_irq_handler(struct i3c_hci *hci)
 	pio_reg_write(INTR_SIGNAL_ENABLE, pio->enabled_irqs);
 	dev_dbg(&hci->master.dev, "PIO_INTR_STATUS %#x/%#x",
 		pio_reg_read(INTR_STATUS), pio_reg_read(INTR_SIGNAL_ENABLE));
-	spin_unlock(&hci->lock);
 	return true;
 }