[PATCH v4 6/9] vfio: selftests: igb: Disable PCIe completion timeout retries

[Josh Hilke]

From: Alex Williamson <alex.williamson@xxxxxxxxxx>

The mix_and_match test intentionally submits TX descriptors with an
unmapped source IOVA so that the DMA read fails.  By default the 82576
re-sends the request after a PCIe completion timeout (datasheet section
8.6.1, GCR.Completion_Timeout_Resend, bit 16, initial value 1b).  On
real hardware this turns a single fault into a stream of retried reads,
keeping PCIe AER and IOMMU error handling busy and interfering with
reset recovery.

Clear GCR.Completion_Timeout_Resend during device initialization so a
failed read fails once and stays failed.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
 tools/testing/selftests/vfio/lib/drivers/igb/igb.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tools/testing/selftests/vfio/lib/drivers/igb/igb.c b/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
index 172c95cea3c8..ac116834bbf6 100644
--- a/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
+++ b/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
@@ -230,6 +230,18 @@ static void igb_init(struct vfio_pci_device *device)
 		vfio_pci_config_writew(device, PCI_COMMAND, cmd_reg);
 	}
 
+	/*
+	 * Disable DMA re-send on PCIe completion timeout (82576 datasheet
+	 * section 8.6.1, GCR.Completion_Timeout_Resend, bit 16).  The
+	 * mix_and_match test intentionally submits descriptors targeting
+	 * unmapped IOVAs; with the default (set) value, the device keeps
+	 * retrying the failed read indefinitely, which keeps PCIe AER and
+	 * IOMMU error handling busy and interferes with reset recovery.
+	 */
+	ctrl = igb_read32(igb, E1000_GCR);
+	ctrl &= ~E1000_GCR_CMPL_TMOUT_RESEND;
+	igb_write32(igb, E1000_GCR, ctrl);
+
 	/* Configure PHY internal loopback for testing. */
 	igb_setup_loopback(igb);
 

-- 
2.55.0.795.g602f6c329a-goog