PCI: pciehp: Tolerate Presence Detect hardwired to zero

This change “PCI: pciehp: Tolerate Presence Detect hardwired to zero” in Linux kernel is authored by Lukas Wunner <lukas [at] wunner.de> on Sat Sep 8 09:59:01 2018 +0200.

PCI: pciehp: Tolerate Presence Detect hardwired to zero

The WiGig Bus Extension (WBE) specification allows tunneling PCIe over
IEEE 802.11.  A product implementing this spec is the wil6210 from
Wilocity (now part of Qualcomm Atheros).  It integrates a PCIe switch
with a wireless network adapter:

  00.0-+              [1ae9:0101]  Upstream Port
       +-00.0-+       [1ae9:0200]  Downstream Port
       |      +-00.0  [168c:0034]  Atheros AR9462 Wireless Network Adapter
       +-02.0         [1ae9:0201]  Downstream Port
       +-03.0         [1ae9:0201]  Downstream Port

Wirelessly attached devices presumably appear below the hotplug ports
with device ID [1ae9:0201].  Oddly, the Downstream Port [1ae9:0200]
leading to the wireless network adapter is likewise Hotplug Capable,
but has its Presence Detect State bit hardwired to zero.  Even if the
Link Active bit is set, Presence Detect is zero, so this cannot be
caused by in-band presence detection but only by broken hardware.

pciehp assumes an empty slot if Presence Detect State is zero,
regardless of Link Active being one.  Consequently, up until v4.18 it
removes the wireless network adapter in pciehp_resume().  From v4.19 it
already does so in pciehp_probe().

Be lenient towards broken hardware and assume the slot is occupied if
Link Active is set:  Introduce pciehp_card_present_or_link_active()
and use it in lieu of pciehp_get_adapter_status() everywhere, except
in pciehp_handle_presence_or_link_change() whose log messages depend
on which of Presence Detect State or Link Active is set.

Remove the Presence Detect State check from __pciehp_enable_slot()
because it is only called if either of Presence Detect State or Link
Active is set.

Caution: There is a possibility that broken hardware exists which has
working Presence Detect but hardwires Link Active to one.  On such
hardware the slot will now incorrectly be considered always occupied.
If such hardware is discovered, this commit can be rolled back and a
quirk can be added which sets is_hotplug_bridge = 0 for [1ae9:0200].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=200839
Reported-and-tested-by: David Yang <mmyangfl@gmail.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Rajat Jain <rajatja@google.com>
Cc: Ashok Raj <ashok.raj@intel.com>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 80696f9.

There are 44 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/pci/hotplug/pciehp.h      |  3 ++-
 drivers/pci/hotplug/pciehp_core.c |  6 +++---
 drivers/pci/hotplug/pciehp_ctrl.c | 10 ++--------
 drivers/pci/hotplug/pciehp_hpc.c  | 25 +++++++++++++++++++------
 4 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
index 8131c08..b9204ef 100644
--- a/drivers/pci/hotplug/pciehp.h
+++ b/drivers/pci/hotplug/pciehp.h
@@ -190,11 +190,12 @@ struct controller {
 
 void pciehp_set_attention_status(struct slot *slot, u8 status);
 void pciehp_get_latch_status(struct slot *slot, u8 *status);
-void pciehp_get_adapter_status(struct slot *slot, u8 *status);
 int pciehp_query_power_fault(struct slot *slot);
 void pciehp_green_led_on(struct slot *slot);
 void pciehp_green_led_off(struct slot *slot);
 void pciehp_green_led_blink(struct slot *slot);
+bool pciehp_card_present(struct controller *ctrl);
+bool pciehp_card_present_or_link_active(struct controller *ctrl);
 int pciehp_check_link_status(struct controller *ctrl);
 bool pciehp_check_link_active(struct controller *ctrl);
 void pciehp_release_ctrl(struct controller *ctrl);
diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index ccaf01e..d2487510 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -158,7 +158,7 @@ static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
 	struct pci_dev *pdev = slot->ctrl->pcie->port;
 
 	pci_config_pm_runtime_get(pdev);
-	pciehp_get_adapter_status(slot, value);
+	*value = pciehp_card_present_or_link_active(slot->ctrl);
 	pci_config_pm_runtime_put(pdev);
 	return 0;
 }
@@ -176,12 +176,12 @@ static int get_adapter_status(struct hotplug_slot *hotplug_slot, u8 *value)
 static void pciehp_check_presence(struct controller *ctrl)
 {
 	struct slot *slot = ctrl->slot;
-	u8 occupied;
+	bool occupied;
 
 	down_read(&ctrl->reset_lock);
 	mutex_lock(&slot->lock);
 
-	pciehp_get_adapter_status(slot, &occupied);
+	occupied = pciehp_card_present_or_link_active(ctrl);
 	if ((occupied && (slot->state == OFF_STATE ||
 			  slot->state == BLINKINGON_STATE)) ||
 	    (!occupied && (slot->state == ON_STATE ||
diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index c4d0f90..1fda6ea 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -223,8 +223,7 @@ void pciehp_handle_disable_request(struct slot *slot)
 void pciehp_handle_presence_or_link_change(struct slot *slot, u32 events)
 {
 	struct controller *ctrl = slot->ctrl;
-	bool link_active;
-	u8 present;
+	bool present, link_active;
 
 	/*
 	 * If the slot is on and presence or link has changed, turn it off.
@@ -253,7 +252,7 @@ void pciehp_handle_presence_or_link_change(struct slot *slot, u32 events)
 
 	/* Turn the slot on if it's occupied or link is up */
 	mutex_lock(&slot->lock);
-	pciehp_get_adapter_status(slot, &present);
+	present = pciehp_card_present(ctrl);
 	link_active = pciehp_check_link_active(ctrl);
 	if (!present && !link_active) {
 		mutex_unlock(&slot->lock);
@@ -286,11 +285,6 @@ static int __pciehp_enable_slot(struct slot *p_slot)
 	u8 getstatus = 0;
 	struct controller *ctrl = p_slot->ctrl;
 
-	pciehp_get_adapter_status(p_slot, &getstatus);
-	if (!getstatus) {
-		ctrl_info(ctrl, "Slot(%s): No adaptern", slot_name(p_slot));
-		return -ENODEV;
-	}
 	if (MRL_SENS(p_slot->ctrl)) {
 		pciehp_get_latch_status(p_slot, &getstatus);
 		if (getstatus) {
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 93003ff..d6cd4fb 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -389,13 +389,27 @@ void pciehp_get_latch_status(struct slot *slot, u8 *status)
 	*status = !!(slot_status & PCI_EXP_SLTSTA_MRLSS);
 }
 
-void pciehp_get_adapter_status(struct slot *slot, u8 *status)
+bool pciehp_card_present(struct controller *ctrl)
 {
-	struct pci_dev *pdev = ctrl_dev(slot->ctrl);
+	struct pci_dev *pdev = ctrl_dev(ctrl);
 	u16 slot_status;
 
 	pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
-	*status = !!(slot_status & PCI_EXP_SLTSTA_PDS);
+	return slot_status & PCI_EXP_SLTSTA_PDS;
+}
+
+/**
+ * pciehp_card_present_or_link_active() - whether given slot is occupied
+ * @ctrl: PCIe hotplug controller
+ *
+ * Unlike pciehp_card_present(), which determines presence solely from the
+ * Presence Detect State bit, this helper also returns true if the Link Active
+ * bit is set.  This is a concession to broken hotplug ports which hardwire
+ * Presence Detect State to zero, such as Wilocity's [1ae9:0200].
+ */
+bool pciehp_card_present_or_link_active(struct controller *ctrl)
+{
+	return pciehp_card_present(ctrl) || pciehp_check_link_active(ctrl);
 }
 
 int pciehp_query_power_fault(struct slot *slot)
@@ -858,7 +872,7 @@ struct controller *pcie_init(struct pcie_device *dev)
 {
 	struct controller *ctrl;
 	u32 slot_cap, link_cap;
-	u8 occupied, poweron;
+	u8 poweron;
 	struct pci_dev *pdev = dev->port;
 
 	ctrl = kzalloc(sizeof(*ctrl), GFP_KERNEL);
@@ -918,9 +932,8 @@ struct controller *pcie_init(struct pcie_device *dev)
 	 * requested yet, so avoid triggering a notification with this command.
 	 */
 	if (POWER_CTRL(ctrl)) {
-		pciehp_get_adapter_status(ctrl->slot, &occupied);
 		pciehp_get_power_status(ctrl->slot, &poweron);
-		if (!occupied && poweron) {
+		if (!pciehp_card_present_or_link_active(ctrl) && poweron) {
 			pcie_disable_notification(ctrl);
 			pciehp_power_off_slot(ctrl->slot);
 		}

The commit for this change in Linux stable tree is 80696f9 (patch).

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