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Subject[v4] PCI: Avoid unsync of LTR mechanism configuration
Date
From: Mingchuang Qiao <mingchuang.qiao@mediatek.com>

In bus scan flow, the "LTR Mechanism Enable" bit of DEVCTL2 register is
configured in pci_configure_ltr(). If device and bridge both support LTR
mechanism, the "LTR Mechanism Enable" bit of device and bridge will be
enabled in DEVCTL2 register. And pci_dev->ltr_path will be set as 1.

If PCIe link goes down when device resets, the "LTR Mechanism Enable" bit
of bridge will change to 0 according to PCIe r5.0, sec 7.5.3.16. However,
the pci_dev->ltr_path value of bridge is still 1.

For following conditions, check and re-configure "LTR Mechanism Enable" bit
of bridge to make "LTR Mechanism Enable" bit match ltr_path value.
-before configuring device's LTR for hot-remove/hot-add
-before restoring device's DEVCTL2 register when restore device state

Signed-off-by: Mingchuang Qiao <mingchuang.qiao@mediatek.com>
---
changes of v4
-fix typo of commit message
-rename: pci_reconfigure_bridge_ltr()->pci_bridge_reconfigure_ltr()
changes of v3
-call pci_reconfigure_bridge_ltr() in probe.c
changes of v2
-modify patch description
-reconfigure bridge's LTR before restoring device DEVCTL2 register
---
drivers/pci/pci.c | 25 +++++++++++++++++++++++++
drivers/pci/pci.h | 1 +
drivers/pci/probe.c | 13 ++++++++++---
3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b9fecc25d213..6bf65d295331 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1437,6 +1437,24 @@ static int pci_save_pcie_state(struct pci_dev *dev)
return 0;
}

+void pci_bridge_reconfigure_ltr(struct pci_dev *dev)
+{
+#ifdef CONFIG_PCIEASPM
+ struct pci_dev *bridge;
+ u32 ctl;
+
+ bridge = pci_upstream_bridge(dev);
+ if (bridge && bridge->ltr_path) {
+ pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2, &ctl);
+ if (!(ctl & PCI_EXP_DEVCTL2_LTR_EN)) {
+ pci_dbg(bridge, "re-enabling LTR\n");
+ pcie_capability_set_word(bridge, PCI_EXP_DEVCTL2,
+ PCI_EXP_DEVCTL2_LTR_EN);
+ }
+ }
+#endif
+}
+
static void pci_restore_pcie_state(struct pci_dev *dev)
{
int i = 0;
@@ -1447,6 +1465,13 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
if (!save_state)
return;

+ /*
+ * Downstream ports reset the LTR enable bit when link goes down.
+ * Check and re-configure the bit here before restoring device.
+ * PCIe r5.0, sec 7.5.3.16.
+ */
+ pci_bridge_reconfigure_ltr(dev);
+
cap = (u16 *)&save_state->cap.data[0];
pcie_capability_write_word(dev, PCI_EXP_DEVCTL, cap[i++]);
pcie_capability_write_word(dev, PCI_EXP_LNKCTL, cap[i++]);
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 5c59365092fa..b3a5e5287cb7 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -111,6 +111,7 @@ void pci_free_cap_save_buffers(struct pci_dev *dev);
bool pci_bridge_d3_possible(struct pci_dev *dev);
void pci_bridge_d3_update(struct pci_dev *dev);
void pci_bridge_wait_for_secondary_bus(struct pci_dev *dev);
+void pci_bridge_reconfigure_ltr(struct pci_dev *dev);

static inline void pci_wakeup_event(struct pci_dev *dev)
{
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 953f15abc850..ade055e9fb58 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2132,9 +2132,16 @@ static void pci_configure_ltr(struct pci_dev *dev)
* Complex and all intermediate Switches indicate support for LTR.
* PCIe r4.0, sec 6.18.
*/
- if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
- ((bridge = pci_upstream_bridge(dev)) &&
- bridge->ltr_path)) {
+ if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) {
+ pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
+ PCI_EXP_DEVCTL2_LTR_EN);
+ dev->ltr_path = 1;
+ return;
+ }
+
+ bridge = pci_upstream_bridge(dev);
+ if (bridge && bridge->ltr_path) {
+ pci_bridge_reconfigure_ltr(dev);
pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
PCI_EXP_DEVCTL2_LTR_EN);
dev->ltr_path = 1;
--
2.18.0
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