[PATCH V4 08/17] i3c: mipi-i3c-hci: Avoid restarting DMA ring after aborting wrong transfer

[Adrian Hunter]

Software ABORT of the DMA ring is used to recover from transfer list
timeouts, but it is inherently racy.  The intended transfer list may
complete just before the ABORT takes effect, causing the subsequent
transfer list to be aborted instead.

In this case, an incomplete transfer list may remain in the ring and has
not yet been processed by hci_dma_dequeue_xfer().  Restarting the DMA
ring at that point can lead to unpredictable results.

Detect when the next queued transfer is not the first entry of a transfer
list and does not belong to the list currently being dequeued.  In that
case, skip restarting the DMA ring and defer recovery until a subsequent
call to hci_dma_dequeue_xfer(), which will safely restart the ring once
the incomplete list is handled.

Signed-off-by: Adrian Hunter <adrian.hunter at intel.com>
---


Changes in V3 and V4:

	None

Changes in V2:

	Renamed completing_xfer to final_xfer


 drivers/i3c/master/mipi-i3c-hci/dma.c | 15 +++++++++++++++
 drivers/i3c/master/mipi-i3c-hci/hci.h |  1 +
 2 files changed, 16 insertions(+)

diff --git a/drivers/i3c/master/mipi-i3c-hci/dma.c b/drivers/i3c/master/mipi-i3c-hci/dma.c
index 83b553e1ab0b..8e27fb6f18f5 100644
--- a/drivers/i3c/master/mipi-i3c-hci/dma.c
+++ b/drivers/i3c/master/mipi-i3c-hci/dma.c
@@ -503,6 +503,7 @@ static int hci_dma_queue_xfer(struct i3c_hci *hci,
 		u32 *ring_data = rh->xfer + rh->xfer_struct_sz * enqueue_ptr;
 
 		xfer->final_xfer = xfer_list + n - 1;
+		xfer->xfer_list_pos = i;
 
 		/* store cmd descriptor */
 		*ring_data++ = xfer->cmd_desc[0];
@@ -669,6 +670,20 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
 		}
 	}
 
+	/*
+	 * A software ABORT may race with transfer completion and abort the next
+	 * transfer list instead. Detect that case, and do not restart the ring.
+	 * It will be handled by a subsequent dequeue.
+	 */
+	if (!did_unqueue) {
+		struct hci_xfer *xfer = rh->src_xfers[rh->done_ptr];
+
+		if (xfer && xfer->xfer_list_pos && xfer->final_xfer != xfer_list->final_xfer) {
+			spin_unlock_irq(&hci->lock);
+			return false;
+		}
+	}
+
 	/* restart the ring */
 	reinit_completion(&rh->op_done);
 	mipi_i3c_hci_resume(hci);
diff --git a/drivers/i3c/master/mipi-i3c-hci/hci.h b/drivers/i3c/master/mipi-i3c-hci/hci.h
index f07fc627d4d2..83d4f13a68a3 100644
--- a/drivers/i3c/master/mipi-i3c-hci/hci.h
+++ b/drivers/i3c/master/mipi-i3c-hci/hci.h
@@ -107,6 +107,7 @@ struct hci_xfer {
 			struct hci_xfer *final_xfer;
 			int ring_number;
 			int ring_entry;
+			int xfer_list_pos;
 		};
 	};
 };
-- 
2.51.0