linux-kernel - [PATCH 2/2] PCI: Do not wait for disconnected devices when resuming

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Date: Mon, 29 Jan 2024 13:27:10 +0200
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci@...r.kernel.org,
	"Maciej W. Rozycki" <macro@...am.me.uk>,
	linux-kernel@...r.kernel.org
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH 2/2] PCI: Do not wait for disconnected devices when resuming

On runtime resume, pci_dev_wait() is called:
  pci_pm_runtime_resume()
    pci_pm_bridge_power_up_actions()
      pci_bridge_wait_for_secondary_bus()
        pci_dev_wait()

While a device is runtime suspended along with its PCIe hierarchy, the
device could get disconnected. In such case, the link will not come up
no matter how log pci_dev_wait() waits for it.

Besides the above mentioned case, there could be other ways to get the
device disconnected while pci_dev_wait() is waiting for the link to
come up.

Make pci_dev_wait() to exit if the device is already disconnected to
avoid unnecessary delay. As disconnected device is not really even a
failure in the same sense as link failing to come up for whatever
reason, return 0 instead of errno.

Also make sure compiler does not become too clever with
dev->error_state and use READ_ONCE() to force a fetch for the
up-to-date value.

Reported-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
Tested-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
 drivers/pci/pci.c | 5 +++++
 drivers/pci/pci.h | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index d8f11a078924..ec9bf6c90312 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1250,6 +1250,11 @@ static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 	for (;;) {
 		u32 id;
 
+		if (pci_dev_is_disconnected(dev)) {
+			pci_dbg(dev, "disconnected; not waiting\n");
+			return 0;
+		}
+
 		pci_read_config_dword(dev, PCI_COMMAND, &id);
 		if (!PCI_POSSIBLE_ERROR(id))
 			break;
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 2336a8d1edab..563a275dff67 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -4,6 +4,8 @@
 
 #include <linux/pci.h>
 
+#include <asm/rwonce.h>
+
 /* Number of possible devfns: 0.0 to 1f.7 inclusive */
 #define MAX_NR_DEVFNS 256
 
@@ -370,7 +372,7 @@ static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
 
 static inline bool pci_dev_is_disconnected(const struct pci_dev *dev)
 {
-	return dev->error_state == pci_channel_io_perm_failure;
+	return READ_ONCE(dev->error_state) == pci_channel_io_perm_failure;
 }
 
 /* pci_dev priv_flags */
-- 
2.39.2