From d11e9de955ea01fe01dce58c7eb090fe0352bced Mon Sep 17 00:00:00 2001
From: Wei Hu <whu@FreeBSD.org>
Date: Sat, 27 Nov 2021 06:42:34 +0000
Subject: [PATCH] Hyper-V: vPCI: Prepopulate device bars

In recent Hyper-V releases on Windows Server 2022, vPCI code does not
initialize the last 4 bit of device bar registers. This behavior change
could result weird problems cuasing PCI code failure when configuring
bars.

Just write all 1's to those bars whose probed values are not the same
as current read ones. This seems to make Hyper-V vPCI and
pci_write_bar() to cooperate correctly on these releases.

Reported by:	khng@freebsd.org
Tested by:	khng@freebsd.org
MFC after:	2 weeks
Sponsored by:	Microsoft

(cherry picked from commit 75412a521f60d4b0393c730ffb284e7c6ff9d2de)
---
 sys/dev/hyperv/pcib/vmbus_pcib.c | 43 ++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/sys/dev/hyperv/pcib/vmbus_pcib.c b/sys/dev/hyperv/pcib/vmbus_pcib.c
index 72e430c946d..c7df3204467 100644
--- a/sys/dev/hyperv/pcib/vmbus_pcib.c
+++ b/sys/dev/hyperv/pcib/vmbus_pcib.c
@@ -1356,6 +1356,47 @@ _hv_pcifront_write_config(struct hv_pci_dev *hpdev, int where, int size,
 	}
 }
 
+/*
+ * The vPCI in some Hyper-V releases do not initialize the last 4
+ * bit of BAR registers. This could result weird problems causing PCI
+ * code fail to configure BAR correctly.
+ *
+ * Just write all 1's to those BARs whose probed values are not zero.
+ * This seems to make the Hyper-V vPCI and pci_write_bar() to cooperate
+ * correctly.
+ */
+
+static void
+vmbus_pcib_prepopulate_bars(struct hv_pcibus *hbus)
+{
+	struct hv_pci_dev *hpdev;
+	int i;
+
+	mtx_lock(&hbus->device_list_lock);
+	TAILQ_FOREACH(hpdev, &hbus->children, link) {
+		for (i = 0; i < 6; i++) {
+			/* Ignore empty bar */
+			if (hpdev->probed_bar[i] == 0)
+				continue;
+
+			uint32_t bar_val = 0;
+
+			_hv_pcifront_read_config(hpdev, PCIR_BAR(i),
+			    4, &bar_val);
+
+			if (hpdev->probed_bar[i] != bar_val) {
+				if (bootverbose)
+					printf("vmbus_pcib: initialize bar %d "
+					    "by writing all 1s\n", i);
+
+				_hv_pcifront_write_config(hpdev, PCIR_BAR(i),
+				    4, 0xffffffff);
+			}
+		}
+	}
+	mtx_unlock(&hbus->device_list_lock);
+}
+
 static void
 vmbus_pcib_set_detaching(void *arg, int pending __unused)
 {
@@ -1479,6 +1520,8 @@ vmbus_pcib_attach(device_t dev)
 	if (ret)
 		goto vmbus_close;
 
+	vmbus_pcib_prepopulate_bars(hbus);
+
 	hbus->pci_bus = device_add_child(dev, "pci", -1);
 	if (!hbus->pci_bus) {
 		device_printf(dev, "failed to create pci bus\n");