[RFC PATCH 2/3] PCI: Enable 10-bit tags support for PCIe devices

[Dongdong Liu <liudongdong3@huawei.com>]

10-Bit Tag capability, introduced in PCIe-4.0 increases the total Tag
field size from 8 bits to 10 bits.

For platforms where the RC supports 10-Bit Tag Completer capability,
it is highly recommended for platform firmware or operating software
that configures PCIe hierarchies to Set the 10-Bit Tag Requester Enable
bit automatically in Endpoints with 10-Bit Tag Requester capability. This
enables the important class of 10-Bit Tag capable adapters that send
Memory Read Requests only to host memory.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 drivers/pci/probe.c | 39 +++++++++++++++++++++++++++++++++++++++
 include/linux/pci.h |  1 +
 2 files changed, 40 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 953f15a..611acce 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2051,6 +2051,44 @@ int pci_configure_extended_tags(struct pci_dev *dev, void *ign)
 	return 0;
 }
 
+static void pci_configure_10bit_tags(struct pci_dev *dev)
+{
+	u32 cap;
+	int ret;
+	struct pci_dev *bridge;
+
+	if (!pci_is_pcie(dev))
+		return;
+
+	ret = pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &cap);
+	if (ret)
+		return;
+
+	if (!(cap & PCI_EXP_DEVCAP2_10BIT_TAG_COMP))
+		return;
+
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) {
+		dev->ext_10bit_tag_comp_path = 1;
+		return;
+	}
+
+	bridge = pci_upstream_bridge(dev);
+	if (bridge && bridge->ext_10bit_tag_comp_path)
+		dev->ext_10bit_tag_comp_path = 1;
+
+	/* 10-Bit Tag Requester Enable in Device Control 2 Register is RsvdP for VF */
+	if (dev->is_virtfn)
+		return;
+
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ENDPOINT &&
+	    dev->ext_10bit_tag_comp_path == 1) {
+		if (cap & PCI_EXP_DEVCAP2_10BIT_TAG_REQ)
+			pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
+					PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN);
+		return;
+	}
+}
+
 /**
  * pcie_relaxed_ordering_enabled - Probe for PCIe relaxed ordering enable
  * @dev: PCI device to query
@@ -2190,6 +2228,7 @@ static void pci_configure_device(struct pci_dev *dev)
 {
 	pci_configure_mps(dev);
 	pci_configure_extended_tags(dev, NULL);
+	pci_configure_10bit_tags(dev);
 	pci_configure_relaxed_ordering(dev);
 	pci_configure_ltr(dev);
 	pci_configure_eetlp_prefix(dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index b32126d..a6dfa2f 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -390,6 +390,7 @@ struct pci_dev {
 #endif
 	unsigned int	eetlp_prefix_path:1;	/* End-to-End TLP Prefix */
 
+	unsigned int	ext_10bit_tag_comp_path:1; /* 10-Bit Tag Completer Supported from root to here */
 	pci_channel_state_t error_state;	/* Current connectivity state */
 	struct device	dev;			/* Generic device interface */
 
-- 
1.9.1