[PATCH V2 0/5] PCI: Enable 10-Bit tag support for PCIe devices

[PATCH V2 0/5] PCI: Enable 10-Bit tag support for PCIe devices

[Dongdong Liu]

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

This patchset is to enable 10-Bit tag for PCIe EP devices (include VF) and
RP devices.

V1->V2: Fix some comments by Christoph.
- Store the devcap2 value in the pci_dev instead of reading it multiple
  times.
- Change pci_info to pci_dbg to avoid the noisy log.
- Rename ext_10bit_tag_comp_path to ext_10bit_tag.
- Fix the compile error.
- Rebased on v5.13-rc1.

Dongdong Liu (5):
  PCI: Use cached Device Capabilities 2 Register
  PCI: Add 10-Bit Tag register definitions
  PCI: Enable 10-Bit tag support for PCIe Endpoint devices
  PCI/IOV: Enable 10-Bit tag support for PCIe VF devices
  PCI: Enable 10-Bit tag support for PCIe RP devices

 drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c |  4 +-
 drivers/pci/iov.c                               |  8 +++
 drivers/pci/pci.c                               |  8 +--
 drivers/pci/pcie/portdrv_pci.c                  | 76 +++++++++++++++++++++++++
 drivers/pci/probe.c                             | 54 ++++++++++++++++--
 include/linux/pci.h                             |  3 +
 include/uapi/linux/pci_regs.h                   |  5 ++
 7 files changed, 144 insertions(+), 14 deletions(-)

--
2.7.4

[PATCH V2 1/5] PCI: Use cached Device Capabilities 2 Register

[Dongdong Liu]

It will make sense to store the devcap2 value in the pci_dev structure
instead of reading Device Capabilities 2 Register multiple times.
So we add pci_init_devcap2() to get the value of devcap2, then use
cached devcap2 in the needed place.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c |  4 +---
 drivers/pci/pci.c                               |  8 +++-----
 drivers/pci/probe.c                             | 18 ++++++++++++------
 include/linux/pci.h                             |  1 +
 4 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
index 6264bc6..704d7c0 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
@@ -6303,7 +6303,6 @@ static int cxgb4_iov_configure(struct pci_dev *pdev, int num_vfs)
 		struct pci_dev *pbridge;
 		struct port_info *pi;
 		char name[IFNAMSIZ];
-		u32 devcap2;
 		u16 flags;
 
 		/* If we want to instantiate Virtual Functions, then our
@@ -6313,10 +6312,9 @@ static int cxgb4_iov_configure(struct pci_dev *pdev, int num_vfs)
 		 */
 		pbridge = pdev->bus->self;
 		pcie_capability_read_word(pbridge, PCI_EXP_FLAGS, &flags);
-		pcie_capability_read_dword(pbridge, PCI_EXP_DEVCAP2, &devcap2);
 
 		if ((flags & PCI_EXP_FLAGS_VERS) < 2 ||
-		    !(devcap2 & PCI_EXP_DEVCAP2_ARI)) {
+		    !(pbridge->devcap2 & PCI_EXP_DEVCAP2_ARI)) {
 			/* Our parent bridge does not support ARI so issue a
 			 * warning and skip instantiating the VFs.  They
 			 * won't be reachable.
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b717680..ed219d7 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3690,7 +3690,7 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
 {
 	struct pci_bus *bus = dev->bus;
 	struct pci_dev *bridge;
-	u32 cap, ctl2;
+	u32 ctl2;
 
 	if (!pci_is_pcie(dev))
 		return -EINVAL;
@@ -3714,19 +3714,17 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
 	while (bus->parent) {
 		bridge = bus->self;
 
-		pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
-
 		switch (pci_pcie_type(bridge)) {
 		/* Ensure switch ports support AtomicOp routing */
 		case PCI_EXP_TYPE_UPSTREAM:
 		case PCI_EXP_TYPE_DOWNSTREAM:
-			if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
+			if (!(bridge->devcap2 & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
 				return -EINVAL;
 			break;
 
 		/* Ensure root port supports all the sizes we care about */
 		case PCI_EXP_TYPE_ROOT_PORT:
-			if ((cap & cap_mask) != cap_mask)
+			if ((bridge->devcap2 & cap_mask) != cap_mask)
 				return -EINVAL;
 			break;
 		}
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 3a62d09..e66bc14 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2098,7 +2098,7 @@ static void pci_configure_ltr(struct pci_dev *dev)
 #ifdef CONFIG_PCIEASPM
 	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
 	struct pci_dev *bridge;
-	u32 cap, ctl;
+	u32 ctl;
 
 	if (!pci_is_pcie(dev))
 		return;
@@ -2106,8 +2106,7 @@ static void pci_configure_ltr(struct pci_dev *dev)
 	/* Read L1 PM substate capabilities */
 	dev->l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
 
-	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &cap);
-	if (!(cap & PCI_EXP_DEVCAP2_LTR))
+	if (!(dev->devcap2 & PCI_EXP_DEVCAP2_LTR))
 		return;
 
 	pcie_capability_read_dword(dev, PCI_EXP_DEVCTL2, &ctl);
@@ -2147,13 +2146,11 @@ static void pci_configure_eetlp_prefix(struct pci_dev *dev)
 #ifdef CONFIG_PCI_PASID
 	struct pci_dev *bridge;
 	int pcie_type;
-	u32 cap;
 
 	if (!pci_is_pcie(dev))
 		return;
 
-	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &cap);
-	if (!(cap & PCI_EXP_DEVCAP2_EE_PREFIX))
+	if (!(dev->devcap2 & PCI_EXP_DEVCAP2_EE_PREFIX))
 		return;
 
 	pcie_type = pci_pcie_type(dev);
@@ -2381,6 +2378,14 @@ void pcie_report_downtraining(struct pci_dev *dev)
 	__pcie_print_link_status(dev, false);
 }
 
+static void pci_init_devcap2(struct pci_dev *dev)
+{
+	if (!pci_is_pcie(dev))
+		return;
+
+	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &dev->devcap2);
+}
+
 static void pci_init_capabilities(struct pci_dev *dev)
 {
 	pci_ea_init(dev);		/* Enhanced Allocation */
@@ -2457,6 +2462,7 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
 {
 	int ret;
 
+	pci_init_devcap2(dev);
 	pci_configure_device(dev);
 
 	device_initialize(&dev->dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index c20211e..3244b0b 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -340,6 +340,7 @@ struct pci_dev {
 	u8		rom_base_reg;	/* Config register controlling ROM */
 	u8		pin;		/* Interrupt pin this device uses */
 	u16		pcie_flags_reg;	/* Cached PCIe Capabilities Register */
+	u32		devcap2;	/* Cached Device Capabilities 2 Register */
 	unsigned long	*dma_alias_mask;/* Mask of enabled devfn aliases */
 
 	struct pci_driver *driver;	/* Driver bound to this device */
-- 
2.7.4

[PATCH V2 2/5] PCI: Add 10-Bit Tag register definitions

[Dongdong Liu]

Add 10-Bit Tag register definitions for use in subsequen patches.
See the PCIe 5.0 spec section 7.5.3.15 and 9.3.3.2.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 include/uapi/linux/pci_regs.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index e709ae8..cf1ddb8 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -648,6 +648,8 @@
 #define  PCI_EXP_DEVCAP2_ATOMIC_COMP64	0x00000100 /* 64b AtomicOp completion */
 #define  PCI_EXP_DEVCAP2_ATOMIC_COMP128	0x00000200 /* 128b AtomicOp completion */
 #define  PCI_EXP_DEVCAP2_LTR		0x00000800 /* Latency tolerance reporting */
+#define  PCI_EXP_DEVCAP2_10BIT_TAG_COMP 0x00010000 /* 10-Bit Tag Completer Supported */
+#define  PCI_EXP_DEVCAP2_10BIT_TAG_REQ  0x00020000 /* 10-Bit Tag Requester Supported */
 #define  PCI_EXP_DEVCAP2_OBFF_MASK	0x000c0000 /* OBFF support mechanism */
 #define  PCI_EXP_DEVCAP2_OBFF_MSG	0x00040000 /* New message signaling */
 #define  PCI_EXP_DEVCAP2_OBFF_WAKE	0x00080000 /* Re-use WAKE# for OBFF */
@@ -661,6 +663,7 @@
 #define  PCI_EXP_DEVCTL2_IDO_REQ_EN	0x0100	/* Allow IDO for requests */
 #define  PCI_EXP_DEVCTL2_IDO_CMP_EN	0x0200	/* Allow IDO for completions */
 #define  PCI_EXP_DEVCTL2_LTR_EN		0x0400	/* Enable LTR mechanism */
+#define  PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN 0x1000 /* 10-Bit Tag Requester Enable */
 #define  PCI_EXP_DEVCTL2_OBFF_MSGA_EN	0x2000	/* Enable OBFF Message type A */
 #define  PCI_EXP_DEVCTL2_OBFF_MSGB_EN	0x4000	/* Enable OBFF Message type B */
 #define  PCI_EXP_DEVCTL2_OBFF_WAKE_EN	0x6000	/* OBFF using WAKE# signaling */
@@ -931,6 +934,7 @@
 /* Single Root I/O Virtualization */
 #define PCI_SRIOV_CAP		0x04	/* SR-IOV Capabilities */
 #define  PCI_SRIOV_CAP_VFM	0x00000001  /* VF Migration Capable */
+#define  PCI_SRIOV_CAP_VF_10BIT_TAG_REQ	0x00000004 /* VF 10-Bit Tag Requester Supported */
 #define  PCI_SRIOV_CAP_INTR(x)	((x) >> 21) /* Interrupt Message Number */
 #define PCI_SRIOV_CTRL		0x08	/* SR-IOV Control */
 #define  PCI_SRIOV_CTRL_VFE	0x0001	/* VF Enable */
@@ -938,6 +942,7 @@
 #define  PCI_SRIOV_CTRL_INTR	0x0004	/* VF Migration Interrupt Enable */
 #define  PCI_SRIOV_CTRL_MSE	0x0008	/* VF Memory Space Enable */
 #define  PCI_SRIOV_CTRL_ARI	0x0010	/* ARI Capable Hierarchy */
+#define  PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN 0x0020 /* VF 10-Bit Tag Requester Enable */
 #define PCI_SRIOV_STATUS	0x0a	/* SR-IOV Status */
 #define  PCI_SRIOV_STATUS_VFM	0x0001	/* VF Migration Status */
 #define PCI_SRIOV_INITIAL_VF	0x0c	/* Initial VFs */
-- 
2.7.4

[PATCH V2 3/5] PCI: Enable 10-Bit tag support for PCIe Endpoint devices

[Dongdong Liu]

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 | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/pci.h |  2 ++
 2 files changed, 38 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index e66bc14..b48b41f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2051,6 +2051,41 @@ int pci_configure_extended_tags(struct pci_dev *dev, void *ign)
 	return 0;
 }
 
+static void pci_configure_10bit_tags(struct pci_dev *dev)
+{
+	struct pci_dev *bridge;
+
+	if (!pci_is_pcie(dev))
+		return;
+
+	if (!(dev->devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP))
+		return;
+
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) {
+		dev->ext_10bit_tag = 1;
+		return;
+	}
+
+	bridge = pci_upstream_bridge(dev);
+	if (bridge && bridge->ext_10bit_tag)
+		dev->ext_10bit_tag = 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 == 1 &&
+	    (dev->devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_REQ)) {
+		pci_dbg(dev, "enabling 10-Bit Tag Requester\n");
+		pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
+					PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN);
+	}
+}
+
 /**
  * pcie_relaxed_ordering_enabled - Probe for PCIe relaxed ordering enable
  * @dev: PCI device to query
@@ -2187,6 +2222,7 @@ 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 3244b0b..7c74d64 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -391,6 +391,8 @@ struct pci_dev {
 #endif
 	unsigned int	eetlp_prefix_path:1;	/* End-to-End TLP Prefix */
 
+	unsigned int	ext_10bit_tag: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 */
 
-- 
2.7.4

[PATCH V2 4/5] PCI/IOV: Enable 10-Bit tag support for PCIe VF devices

[Dongdong Liu]

Enable VF 10-Bit Tag Requester when it's upstream component support
10-bit Tag Completer.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 drivers/pci/iov.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index afc06e6..3eb4348 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -627,6 +627,10 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 
 	pci_iov_set_numvfs(dev, nr_virtfn);
 	iov->ctrl |= PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE;
+	if ((iov->cap & PCI_SRIOV_CAP_VF_10BIT_TAG_REQ) &&
+	    dev->ext_10bit_tag)
+		iov->ctrl |= PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN;
+
 	pci_cfg_access_lock(dev);
 	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
 	msleep(100);
@@ -643,6 +647,8 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 
 err_pcibios:
 	iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
+	if (iov->ctrl & PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN)
+		iov->ctrl &= ~PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN;
 	pci_cfg_access_lock(dev);
 	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
 	ssleep(1);
@@ -675,6 +681,8 @@ static void sriov_disable(struct pci_dev *dev)
 
 	sriov_del_vfs(dev);
 	iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
+	if (iov->ctrl & PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN)
+		iov->ctrl &= ~PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN;
 	pci_cfg_access_lock(dev);
 	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
 	ssleep(1);
-- 
2.7.4

Re: [PATCH V2 1/5] PCI: Use cached Device Capabilities 2 Register

[Christoph Hellwig]

On Tue, May 11, 2021 at 11:09:00PM +0800, Dongdong Liu wrote:
> It will make sense to store the devcap2 value in the pci_dev structure
> instead of reading Device Capabilities 2 Register multiple times.
> So we add pci_init_devcap2() to get the value of devcap2, then use
> cached devcap2 in the needed place.

This looks sensible.  Should the devcap field maybe grow a pcie_
prefix?  What about caching PCI_EXP_DEVCAP as well while you're at it?

Re: [PATCH V2 1/5] PCI: Use cached Device Capabilities 2 Register

[Dongdong Liu]

Hi Christoph
Many thanks for your review.
On 2021/5/11 23:26, Christoph Hellwig wrote:
> On Tue, May 11, 2021 at 11:09:00PM +0800, Dongdong Liu wrote:
>> It will make sense to store the devcap2 value in the pci_dev structure
>> instead of reading Device Capabilities 2 Register multiple times.
>> So we add pci_init_devcap2() to get the value of devcap2, then use
>> cached devcap2 in the needed place.
>
> This looks sensible.  Should the devcap field maybe grow a pcie_
> prefix?
Yes, It will be good to use pcie_prefix.
> What about caching PCI_EXP_DEVCAP as well while you're at it?
Make sense, will do.

Thanks,
Dongdong
>

[PATCH V2 1/5] PCI: Use cached Device Capabilities 2 Register

[Dongdong Liu]

It will make sense to store the devcap2 value in the pci_dev structure
instead of reading Device Capabilities 2 Register multiple times.
So we add pci_init_devcap2() to get the value of devcap2, then use
cached devcap2 in the needed place.

Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
---
 drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c |  4 +---
 drivers/pci/pci.c                               |  8 +++-----
 drivers/pci/probe.c                             | 18 ++++++++++++------
 include/linux/pci.h                             |  1 +
 4 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
index 6264bc6..704d7c0 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
@@ -6303,7 +6303,6 @@ static int cxgb4_iov_configure(struct pci_dev *pdev, int num_vfs)
 		struct pci_dev *pbridge;
 		struct port_info *pi;
 		char name[IFNAMSIZ];
-		u32 devcap2;
 		u16 flags;
 
 		/* If we want to instantiate Virtual Functions, then our
@@ -6313,10 +6312,9 @@ static int cxgb4_iov_configure(struct pci_dev *pdev, int num_vfs)
 		 */
 		pbridge = pdev->bus->self;
 		pcie_capability_read_word(pbridge, PCI_EXP_FLAGS, &flags);
-		pcie_capability_read_dword(pbridge, PCI_EXP_DEVCAP2, &devcap2);
 
 		if ((flags & PCI_EXP_FLAGS_VERS) < 2 ||
-		    !(devcap2 & PCI_EXP_DEVCAP2_ARI)) {
+		    !(pbridge->devcap2 & PCI_EXP_DEVCAP2_ARI)) {
 			/* Our parent bridge does not support ARI so issue a
 			 * warning and skip instantiating the VFs.  They
 			 * won't be reachable.
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b717680..ed219d7 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3690,7 +3690,7 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
 {
 	struct pci_bus *bus = dev->bus;
 	struct pci_dev *bridge;
-	u32 cap, ctl2;
+	u32 ctl2;
 
 	if (!pci_is_pcie(dev))
 		return -EINVAL;
@@ -3714,19 +3714,17 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask)
 	while (bus->parent) {
 		bridge = bus->self;
 
-		pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
-
 		switch (pci_pcie_type(bridge)) {
 		/* Ensure switch ports support AtomicOp routing */
 		case PCI_EXP_TYPE_UPSTREAM:
 		case PCI_EXP_TYPE_DOWNSTREAM:
-			if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
+			if (!(bridge->devcap2 & PCI_EXP_DEVCAP2_ATOMIC_ROUTE))
 				return -EINVAL;
 			break;
 
 		/* Ensure root port supports all the sizes we care about */
 		case PCI_EXP_TYPE_ROOT_PORT:
-			if ((cap & cap_mask) != cap_mask)
+			if ((bridge->devcap2 & cap_mask) != cap_mask)
 				return -EINVAL;
 			break;
 		}
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 3a62d09..e66bc14 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2098,7 +2098,7 @@ static void pci_configure_ltr(struct pci_dev *dev)
 #ifdef CONFIG_PCIEASPM
 	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
 	struct pci_dev *bridge;
-	u32 cap, ctl;
+	u32 ctl;
 
 	if (!pci_is_pcie(dev))
 		return;
@@ -2106,8 +2106,7 @@ static void pci_configure_ltr(struct pci_dev *dev)
 	/* Read L1 PM substate capabilities */
 	dev->l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
 
-	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &cap);
-	if (!(cap & PCI_EXP_DEVCAP2_LTR))
+	if (!(dev->devcap2 & PCI_EXP_DEVCAP2_LTR))
 		return;
 
 	pcie_capability_read_dword(dev, PCI_EXP_DEVCTL2, &ctl);
@@ -2147,13 +2146,11 @@ static void pci_configure_eetlp_prefix(struct pci_dev *dev)
 #ifdef CONFIG_PCI_PASID
 	struct pci_dev *bridge;
 	int pcie_type;
-	u32 cap;
 
 	if (!pci_is_pcie(dev))
 		return;
 
-	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &cap);
-	if (!(cap & PCI_EXP_DEVCAP2_EE_PREFIX))
+	if (!(dev->devcap2 & PCI_EXP_DEVCAP2_EE_PREFIX))
 		return;
 
 	pcie_type = pci_pcie_type(dev);
@@ -2381,6 +2378,14 @@ void pcie_report_downtraining(struct pci_dev *dev)
 	__pcie_print_link_status(dev, false);
 }
 
+static void pci_init_devcap2(struct pci_dev *dev)
+{
+	if (!pci_is_pcie(dev))
+		return;
+
+	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP2, &dev->devcap2);
+}
+
 static void pci_init_capabilities(struct pci_dev *dev)
 {
 	pci_ea_init(dev);		/* Enhanced Allocation */
@@ -2457,6 +2462,7 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
 {
 	int ret;
 
+	pci_init_devcap2(dev);
 	pci_configure_device(dev);
 
 	device_initialize(&dev->dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index c20211e..3244b0b 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -340,6 +340,7 @@ struct pci_dev {
 	u8		rom_base_reg;	/* Config register controlling ROM */
 	u8		pin;		/* Interrupt pin this device uses */
 	u16		pcie_flags_reg;	/* Cached PCIe Capabilities Register */
+	u32		devcap2;	/* Cached Device Capabilities 2 Register */
 	unsigned long	*dma_alias_mask;/* Mask of enabled devfn aliases */
 
 	struct pci_driver *driver;	/* Driver bound to this device */
-- 
2.7.4