linux-kernel - [PATCH] PCI/PM: Print the pci config space of devices before suspend

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Date:   Mon, 13 Jan 2020 14:07:24 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     linux-pci@...r.kernel.org
Cc:     Chen Yu <yu.c.chen@...el.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] PCI/PM: Print the pci config space of devices before suspend

The pci config space was found to be insane during resume
from hibernation(S4, or suspend to disk) on a VM:

 serial 0000:00:16.3: restoring config space at offset 0x14
 (was 0x9104e000, writing 0xffffffff)

Either the snapshot on the disk has been scribbled or the pci
config space becomes invalid before suspend. To narrow down
and benefit future debugging, print the pci config space
being saved before suspend, which is symmetric to the log
in pci_restore_config_dword().

Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Len Brown <lenb@...nel.org>
Cc: linux-pci@...r.kernel.org
Cc: linux-pm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
 drivers/pci/pci.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e87196cc1a7f..34cde70440c3 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1372,8 +1372,11 @@ int pci_save_state(struct pci_dev *dev)
 {
 	int i;
 	/* XXX: 100% dword access ok here? */
-	for (i = 0; i < 16; i++)
+	for (i = 0; i < 16; i++) {
 		pci_read_config_dword(dev, i * 4, &dev->saved_config_space[i]);
+		pci_dbg(dev, "saving config space at offset %#x (reading %#x)\n",
+			i * 4, dev->saved_config_space[i]);
+	}
 	dev->state_saved = true;
 
 	i = pci_save_pcie_state(dev);
-- 
2.17.1