[PATCH v2 2/2] NTB: epf: propagate MW command errors while status is reliable

[Avi Weiss <thnkslprpt@gmail.com>]

ntb_epf_mw_set_trans() and ntb_epf_mw_clear_trans() discard command
errors even when the endpoint explicitly rejects a request.

A timed-out command may still complete on the endpoint. Propagating
that timeout can cause callers to free DMA buffers before the mapping
completes. A late completion may also be mistaken for the result of a
subsequent command.

Record the first command timeout and propagate MW command errors only
while completion status remains reliable. Preserve the original MW
success-return behavior after a timeout to avoid releasing buffers
based on ambiguous results.

Fixes: 812ce2f8d14e ("NTB: Add support for EPF PCI Non-Transparent Bridge")
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---
 drivers/ntb/hw/epf/ntb_hw_epf.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c
index da7fbe1800656..455bcefc7c13e 100644
--- a/drivers/ntb/hw/epf/ntb_hw_epf.c
+++ b/drivers/ntb/hw/epf/ntb_hw_epf.c
@@ -102,6 +102,7 @@ struct ntb_epf_dev {
 	struct device *dev;
 	/* Mutex to protect providing commands to NTB EPF */
 	struct mutex cmd_lock;
+	bool cmd_status_unreliable;
 
 	const enum pci_barno *barno_map;
 
@@ -148,6 +149,7 @@ static int ntb_epf_send_command_locked(struct ntb_epf_dev *ndev, u32 command,
 			break;
 
 		if (WARN_ON(timedout)) {
+			ndev->cmd_status_unreliable = true;
 			ret = -ETIMEDOUT;
 			break;
 		}
@@ -156,6 +158,13 @@ static int ntb_epf_send_command_locked(struct ntb_epf_dev *ndev, u32 command,
 	}
 
 	writew(0, ndev->ctrl_reg + NTB_EPF_CMD_STATUS);
+	/*
+	 * After a timeout, a status may refer to an earlier command.
+	 * MW callers may free buffers on error, so retain old semantics.
+	 */
+	if (ndev->cmd_status_unreliable &&
+	    (command == CMD_CONFIGURE_MW || command == CMD_TEARDOWN_MW))
+		ret = 0;
 
 	return ret;
 }
@@ -485,7 +494,7 @@ static int ntb_epf_mw_set_trans(struct ntb_dev *ntb, int pidx, int idx,
 	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
 	struct device *dev = ndev->dev;
 	resource_size_t mw_size;
-	int bar;
+	int bar, ret;
 
 	if (pidx != NTB_DEF_PEER_IDX) {
 		dev_err(dev, "Unsupported Peer ID %d\n", pidx);
@@ -509,19 +518,19 @@ static int ntb_epf_mw_set_trans(struct ntb_dev *ntb, int pidx, int idx,
 	writel(upper_32_bits(addr), ndev->ctrl_reg + NTB_EPF_UPPER_ADDR);
 	writel(lower_32_bits(size), ndev->ctrl_reg + NTB_EPF_LOWER_SIZE);
 	writel(upper_32_bits(size), ndev->ctrl_reg + NTB_EPF_UPPER_SIZE);
-	ntb_epf_send_command_locked(ndev, CMD_CONFIGURE_MW, idx);
+	ret = ntb_epf_send_command_locked(ndev, CMD_CONFIGURE_MW, idx);
 	mutex_unlock(&ndev->cmd_lock);
 
-	return 0;
+	return ret;
 }
 
 static int ntb_epf_mw_clear_trans(struct ntb_dev *ntb, int pidx, int idx)
 {
 	struct ntb_epf_dev *ndev = ntb_ndev(ntb);
 	struct device *dev = ndev->dev;
-	int ret = 0;
+	int ret;
 
-	ntb_epf_send_command(ndev, CMD_TEARDOWN_MW, idx);
+	ret = ntb_epf_send_command(ndev, CMD_TEARDOWN_MW, idx);
 	if (ret)
 		dev_err(dev, "Failed to teardown memory window\n");
 
-- 
2.43.0