[PATCH 5/8] selftests/vfio: igb: Disable PCIe completion timeout retries

[Alex Williamson <alex.williamson@nvidia.com>]

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
subsequent reset recovery.

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

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
---
 tools/testing/selftests/vfio/lib/drivers/igb/igb.c   | 12 ++++++++++++
 .../selftests/vfio/lib/drivers/igb/registers.h       |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/tools/testing/selftests/vfio/lib/drivers/igb/igb.c b/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
index 2297382d7c26..9f93ec7ba8bc 100644
--- a/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
+++ b/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
@@ -213,6 +213,18 @@ 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, IGB_GCR);
+	ctrl &= ~IGB_GCR_CMPL_TMOUT_RESEND;
+	igb_write32(igb, IGB_GCR, ctrl);
+
 	/* Configure PHY internal loopback for testing. */
 	if (igb_setup_loopback(igb))
 		return;
diff --git a/tools/testing/selftests/vfio/lib/drivers/igb/registers.h b/tools/testing/selftests/vfio/lib/drivers/igb/registers.h
index 139f1c2e6fdd..45f71dc26e24 100644
--- a/tools/testing/selftests/vfio/lib/drivers/igb/registers.h
+++ b/tools/testing/selftests/vfio/lib/drivers/igb/registers.h
@@ -73,6 +73,8 @@
 
 #define IGB_RAH0 0x05404 /* Receive Address High 0 */
 #define IGB_VMOLR0 0x05AD0 /* VM Offload Layout Register 0 */
+#define IGB_GCR 0x05B00 /* PCIe Control */
+#define IGB_GCR_CMPL_TMOUT_RESEND BIT(16) /* Re-send on completion timeout */
 
 #define IGB_VMOLR_LPE 0x00010000 /* Long Packet Enable */
 #define IGB_VMOLR_BAM 0x08000000 /* Broadcast Accept Mode */
-- 
2.51.0