From: Nathan Rossi <nathan.rossi@xxxxxxxx>
The Pericom PI7C9X2G404 PCIe switch has an errata for ACS P2P Request
Redirect behaviour when used in the cut-through forwarding mode. The
recommended work around for this issue is to use the switch in store and
forward mode. The errata results in packets being queued and not being
delivered upstream, this can be observed as very poor downstream device
performance and/or dropped device generated data/interrupts.
This change adds a fixup specific to this switch that when enabling or
resuming the downstream port it checks if it has enabled ACS P2P Request
Redirect, and if so changes the device (via the upstream port) to use
the store and forward operating mode.
Signed-off-by: Nathan Rossi <nathan.rossi@xxxxxxxx>
---
Changes in v2:
- Added DECLARE_PCI_FIXUP_RESUME to handle applying fixup upon resume as
switch operation may have been reset or ACS configuration may have
changed
---
drivers/pci/quirks.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 48 insertions(+)
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index e5089af8ad..5849b7046b 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -5790,3 +5790,51 @@ static void apex_pci_fixup_class(struct pci_dev *pdev)
}
DECLARE_PCI_FIXUP_CLASS_HEADER(0x1ac1, 0x089a,
PCI_CLASS_NOT_DEFINED, 8, apex_pci_fixup_class);
+
+/*
+ * Pericom PI7C9X2G404 switch errata E5 - ACS P2P Request Redirect is not
+ * functional
+ *
+ * When ACS P2P Request Redirect is enabled and bandwidth is not balanced
+ * between upstream and downstream ports, packets are queued in an internal
+ * buffer until CPLD packet. The workaround is to use the switch in store and
+ * forward mode.
+ */
+#define PI7C9X2G404_MODE_REG 0x74
+#define PI7C9X2G404_STORE_FORWARD_MODE BIT(0)
+static void pci_fixup_pericom_acs_store_forward(struct pci_dev *pdev)
+{
+ struct pci_dev *upstream;
+ u16 val;
+
+ /* Downstream ports only */
+ if (pci_pcie_type(pdev) != PCI_EXP_TYPE_DOWNSTREAM)
+ return;
+
+ /* Check for ACS P2P Request Redirect use */
+ if (!pdev->acs_cap)
+ return;
+ pci_read_config_word(pdev, pdev->acs_cap + PCI_ACS_CTRL, &val);
+ if (!(val & PCI_ACS_RR))
+ return;
+
+ upstream = pci_upstream_bridge(pdev);
+ if (!upstream)
+ return;
+
+ pci_read_config_word(upstream, PI7C9X2G404_MODE_REG, &val);
+ if (!(val & PI7C9X2G404_STORE_FORWARD_MODE)) {
+ pci_info(upstream, "Setting PI7C9X2G404 store-forward mode\n");
+ /* Enable store-foward mode */
+ pci_write_config_word(upstream, PI7C9X2G404_MODE_REG, val |
+ PI7C9X2G404_STORE_FORWARD_MODE);
+ }
+}
+/*
+ * Apply fixup on enable and on resume, in order to apply the fix up whenever
+ * ACS configuration changes or switch mode is reset
+ */
+DECLARE_PCI_FIXUP_ENABLE(PCI_VENDOR_ID_PERICOM, 0x2404,
+ pci_fixup_pericom_acs_store_forward);
+DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_PERICOM, 0x2404,
+ pci_fixup_pericom_acs_store_forward);
---
2.33.0
