[RFC PATCH 1/1] PCI: Add Extended Tag + MRRS quirk for Xeon 6

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

Disallow Extended Tags and Max Read Request Size (MRRS) larger than
128B for devices under Xeon 6 Root Ports if the Root Port is bifurcated
to x2. Also, 10-Bit Tag Requester should be disallowed for device
underneath these Root Ports but there is currently no 10-Bit Tag
support in the kernel.

The normal path that writes MRRS is through
pcie_bus_configure_settings() -> pcie_bus_configure_set() ->
pcie_write_mrrs() and contains a few early returns that are based on
the value of pcie_bus_config. Overriding such checks with the host
bridge flag check on each level seems messy. Thus, simply ensure MRRS
is always written in pci_configure_device() if a device requiring the
quirk is detected.

Link: https://cdrdv2.intel.com/v1/dl/getContent/837176
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---

The normal path that writes MRRS is somewhat convoluted so I ensure MRRS
gets written in a more direct way, I'm not sure if that's the best
approach. Thus sending this as RFC.

 drivers/pci/pci.c    | 15 ++++++++-------
 drivers/pci/probe.c  |  8 +++++++-
 drivers/pci/quirks.c | 27 +++++++++++++++++++++++++++
 include/linux/pci.h  |  1 +
 4 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 869d204a70a3..81ddad81ccb8 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5913,7 +5913,7 @@ EXPORT_SYMBOL(pcie_get_readrq);
 int pcie_set_readrq(struct pci_dev *dev, int rq)
 {
 	u16 v;
-	int ret;
+	int ret, max_mrrs = 4096;
 	struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
 
 	if (rq < 128 || rq > 4096 || !is_power_of_2(rq))
@@ -5933,13 +5933,14 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
 
 	v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, ffs(rq) - 8);
 
-	if (bridge->no_inc_mrrs) {
-		int max_mrrs = pcie_get_readrq(dev);
+	if (bridge->no_inc_mrrs)
+		max_mrrs = pcie_get_readrq(dev);
+	if (bridge->only_128b_mrrs)
+		max_mrrs = 128;
 
-		if (rq > max_mrrs) {
-			pci_info(dev, "can't set Max_Read_Request_Size to %d; max is %d\n", rq, max_mrrs);
-			return -EINVAL;
-		}
+	if (rq > max_mrrs) {
+		pci_info(dev, "can't set Max_Read_Request_Size to %d; max is %d\n", rq, max_mrrs);
+		return -EINVAL;
 	}
 
 	ret = pcie_capability_clear_and_set_word(dev, PCI_EXP_DEVCTL,
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index b6536ed599c3..ceaa34b0525b 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2342,7 +2342,11 @@ static void pci_configure_serr(struct pci_dev *dev)
 
 static void pci_configure_device(struct pci_dev *dev)
 {
+	struct pci_host_bridge *host_bridge = pci_find_host_bridge(dev->bus);
+
 	pci_configure_mps(dev);
+	if (host_bridge && host_bridge->only_128b_mrrs)
+		pcie_set_readrq(dev, 128);
 	pci_configure_extended_tags(dev, NULL);
 	pci_configure_relaxed_ordering(dev);
 	pci_configure_ltr(dev);
@@ -2851,13 +2855,15 @@ static void pcie_write_mps(struct pci_dev *dev, int mps)
 
 static void pcie_write_mrrs(struct pci_dev *dev)
 {
+	struct pci_host_bridge *host_bridge = pci_find_host_bridge(dev->bus);
 	int rc, mrrs;
 
 	/*
 	 * In the "safe" case, do not configure the MRRS.  There appear to be
 	 * issues with setting MRRS to 0 on a number of devices.
 	 */
-	if (pcie_bus_config != PCIE_BUS_PERFORMANCE)
+	if (pcie_bus_config != PCIE_BUS_PERFORMANCE &&
+	    (!host_bridge || !host_bridge->only_128b_mrrs))
 		return;
 
 	/*
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index b84ff7bade82..987cd94028e1 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -5564,6 +5564,33 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_SERVERWORKS, 0x0144, quirk_no_ext_tags);
 DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_SERVERWORKS, 0x0420, quirk_no_ext_tags);
 DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_SERVERWORKS, 0x0422, quirk_no_ext_tags);
 
+static void quirk_pcie2x_no_tags_no_mrrs(struct pci_dev *pdev)
+{
+	struct pci_host_bridge *bridge = pci_find_host_bridge(pdev->bus);
+	u32 linkcap;
+
+	if (!bridge)
+		return;
+
+	pcie_capability_read_dword(pdev, PCI_EXP_LNKCAP, &linkcap);
+	if (FIELD_GET(PCI_EXP_LNKCAP_MLW, linkcap) != 0x2)
+		return;
+
+	bridge->no_ext_tags = 1;
+	bridge->only_128b_mrrs = 1;
+	pci_info(pdev, "Disabling Extended Tags and forcing MRRS to 128B (performance reasons due to 2x PCIe link)\n");
+}
+
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db0, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db1, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db2, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db3, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db6, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db7, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db8, quirk_pcie2x_no_tags_no_mrrs);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x0db9, quirk_pcie2x_no_tags_no_mrrs);
+
+
 #ifdef CONFIG_PCI_ATS
 static void quirk_no_ats(struct pci_dev *pdev)
 {
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 47b31ad724fa..def29c8c0f84 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -601,6 +601,7 @@ struct pci_host_bridge {
 	unsigned int	ignore_reset_delay:1;	/* For entire hierarchy */
 	unsigned int	no_ext_tags:1;		/* No Extended Tags */
 	unsigned int	no_inc_mrrs:1;		/* No Increase MRRS */
+	unsigned int	only_128b_mrrs:1;	/* Only 128B MRRS */
 	unsigned int	native_aer:1;		/* OS may use PCIe AER */
 	unsigned int	native_pcie_hotplug:1;	/* OS may use PCIe hotplug */
 	unsigned int	native_shpc_hotplug:1;	/* OS may use SHPC hotplug */

base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
-- 
2.39.5