Gaggery Tsai has uploaded this change for review.

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src/soc/intel/common/block/pcie: Add a workaround for ThP2 9260

This patch adds a workaround for ThP2. The PCIe root port LCTL2.TLS
is by default GEN1 and ThP has bad synchronization on polarity
inversion. When the root port request for speed change, ThP doesn’t
confirm the request, and both sides are moving to polling after
timeout, hot reset is issued, and then most of the CFG space is
initialized. From the observation, CCC/ECPM/LTR would be reset to
default but CCC/ECPM of root port and end devices have been
reconfigured in pci_scan. The LTR configuration for root port
is still missing.

BUG=B:117618636
BRANCH=None
TEST=Add THP2_9260_WORKAROUND in Atlas configuration & emerge-atlas
     coreboot chromeos-bootimage &  Warm/cold reset for 10 times and
     didn't see unsupported request related AER error messages &
     $lspci -vvs 00:1c.0|grep LTR and ensure LTR+ is present.

Change-Id: Id5d2814488fbc9db927edb2ead972b73ebc336ce
Signed-off-by: Gaggery Tsai <gaggery.tsai@intel.com>
---
M src/soc/intel/common/block/pcie/Kconfig
M src/soc/intel/common/block/pcie/pcie.c
2 files changed, 29 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/86/30486/1

diff --git a/src/soc/intel/common/block/pcie/Kconfig b/src/soc/intel/common/block/pcie/Kconfig
index aa32324..36915fa 100644
--- a/src/soc/intel/common/block/pcie/Kconfig
+++ b/src/soc/intel/common/block/pcie/Kconfig
@@ -13,3 +13,8 @@
 	  Enable debug logs in PCIe module. Allows debug information on memory
 	  base and limit, prefetchable memory base and limit, prefetchable memory
 	  base upper 32 bits and prefetchable memory limit upper 32 bits.
+
+config THP2_9260_WORKAROUND
+	bool
+	help
+	  THP2 workaround
diff --git a/src/soc/intel/common/block/pcie/pcie.c b/src/soc/intel/common/block/pcie/pcie.c
index 3ebb4f6..07a2321 100644
--- a/src/soc/intel/common/block/pcie/pcie.c
+++ b/src/soc/intel/common/block/pcie/pcie.c
@@ -28,12 +28,36 @@
 /* PCI-E Sub-System ID */
 #define PCIE_SUBSYSTEM_VENDOR_ID	0x94
 
+/*
+ * Check the LTR for root port and enable it
+ */
+static void pciexp_enable_root_port_ltr(struct device *root, unsigned root_cap)
+{
+	u16 root_ltr;
+	unsigned int val;
+
+	val = pci_read_config16(root, root_cap + PCI_EXP_DEV_CAP2_OFFSET);
+
+	if (val & LTR_MECHANISM_SUPPORT) {
+		root_ltr = pci_read_config16(root, root_cap + PCI_EXP_DEV_CTL_STS2_CAP_OFFSET);
+		root_ltr |= LTR_MECHANISM_EN;
+		pci_write_config16(root, root_cap + PCI_EXP_DEV_CTL_STS2_CAP_OFFSET, root_ltr);
+	}
+}
+
 static void pch_pcie_init(struct device *dev)
 {
 	u16 reg16;
+	unsigned int dev_cap;
 
 	printk(BIOS_DEBUG, "Initializing PCH PCIe bridge.\n");
 
+	if (IS_ENABLED(CONFIG_THP2_9260_WORKAROUND)) {
+		dev_cap = pci_find_capability(dev, PCI_CAP_ID_PCIE);
+		if (dev_cap)
+			pciexp_enable_root_port_ltr(dev, dev_cap);
+	}
+
 	/* Enable SERR */
 	pci_or_config32(dev, PCI_COMMAND, PCI_COMMAND_SERR);
 

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