LinuxKPI: Add pcie_capability_clear_and_set_word() function

It does a Read-Modify-Write operation using clear and set bitmasks on
PCI Express Capability Register at pos. As certain PCI Express
Capability Registers are accessed concurrently in RMW fashion, hence
require locking which is handled transparently to the caller.

Sponsored by:	Serenity CyberSecurity, LLC
Reviewed by:	manu, bz
MFC after:	1 week
MFC TODO:	Move pcie_cap_lock to bottom to preserve KBI compatibility
Differential Revision:	https://reviews.freebsd.org/D42821

2 files changed, 23 insertions, 16 deletions

diff --git a/sys/compat/linuxkpi/common/include/linux/pci.h b/sys/compat/linuxkpi/common/include/linux/pci.h
index aa99b050ffd9..9c7e39bf4a42 100644
--- a/sys/compat/linuxkpi/common/include/linux/pci.h
+++ b/sys/compat/linuxkpi/common/include/linux/pci.h
@@ -347,6 +347,7 @@ struct pci_dev {
 	size_t			romlen;
 	struct msi_desc		**msi_desc;
 	char			*path_name;
+	spinlock_t		pcie_cap_lock;
 
 	TAILQ_HEAD(, pci_mmio_region)	mmio;
 };
@@ -1012,35 +1013,38 @@ pcie_capability_write_word(struct pci_dev *dev, int pos, u16 val)
 }
 
 static inline int
-pcie_capability_set_word(struct pci_dev *dev, int pos, uint16_t val)
+pcie_capability_clear_and_set_word(struct pci_dev *dev, int pos,
+    uint16_t clear, uint16_t set)
 {
 	int error;
 	uint16_t v;
 
+	if (pos == PCI_EXP_LNKCTL || pos == PCI_EXP_RTCTL)
+		spin_lock(&dev->pcie_cap_lock);
+
 	error = pcie_capability_read_word(dev, pos, &v);
-	if (error != 0)
-		return (error);
+	if (error == 0) {
+		v &= ~clear;
+		v |= set;
+		error = pcie_capability_write_word(dev, pos, v);
+	}
 
-	v |= val;
+	if (pos == PCI_EXP_LNKCTL || pos == PCI_EXP_RTCTL)
+		spin_unlock(&dev->pcie_cap_lock);
 
-	error = pcie_capability_write_word(dev, pos, v);
 	return (error);
 }
 
 static inline int
-pcie_capability_clear_word(struct pci_dev *dev, int pos, uint16_t val)
+pcie_capability_set_word(struct pci_dev *dev, int pos, uint16_t val)
 {
-	int error;
-	uint16_t v;
-
-	error = pcie_capability_read_word(dev, pos, &v);
-	if (error != 0)
-		return (error);
-
-	v &= ~val;
+	return (pcie_capability_clear_and_set_word(dev, pos, 0, val));
+}
 
-	error = pcie_capability_write_word(dev, pos, v);
-	return (error);
+static inline int
+pcie_capability_clear_word(struct pci_dev *dev, int pos, uint16_t val)
+{
+	return (pcie_capability_clear_and_set_word(dev, pos, val, 0));
 }
 
 static inline int pcie_get_minimum_link(struct pci_dev *dev,
diff --git a/sys/compat/linuxkpi/common/src/linux_pci.c b/sys/compat/linuxkpi/common/src/linux_pci.c
index 4cd28fac15d3..825ebe319b1a 100644
--- a/sys/compat/linuxkpi/common/src/linux_pci.c
+++ b/sys/compat/linuxkpi/common/src/linux_pci.c
@@ -525,6 +525,7 @@ linux_pci_attach_device(device_t dev, struct pci_driver *pdrv,
 		goto out_dma_init;
 
 	TAILQ_INIT(&pdev->mmio);
+	spin_lock_init(&pdev->pcie_cap_lock);
 
 	spin_lock(&pci_lock);
 	list_add(&pdev->links, &pci_devices);
@@ -539,6 +540,7 @@ linux_pci_attach_device(device_t dev, struct pci_driver *pdrv,
 
 out_probe:
 	free(pdev->bus, M_DEVBUF);
+	spin_lock_destroy(&pdev->pcie_cap_lock);
 	linux_pdev_dma_uninit(pdev);
 out_dma_init:
 	spin_lock(&pci_lock);
@@ -579,6 +581,7 @@ linux_pci_detach_device(struct pci_dev *pdev)
 	spin_lock(&pci_lock);
 	list_del(&pdev->links);
 	spin_unlock(&pci_lock);
+	spin_lock_destroy(&pdev->pcie_cap_lock);
 	put_device(&pdev->dev);
 
 	return (0);