[PATCH v2 05/11] PCI/ATS: Gather checks into pci_ats_supported()

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

IOMMU drivers need to perform several tests when checking if a device
supports ATS.  Move them all into a new function that returns true when
a device and its host bridge support ATS.

Since pci_enable_ats() now calls pci_ats_supported(), the following
new checks are now common:
* whether a device is trusted.  Devices plugged into external-facing
  ports such as thunderbolt are untrusted.
* whether the host bridge supports ATS, which defaults to true unless
  the firmware description states that ATS isn't supported by the host
  bridge.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
 drivers/pci/ats.c       | 30 +++++++++++++++++++++++++++++-
 include/linux/pci-ats.h |  3 +++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index 390e92f2d8d1..bbfd0d42b8b9 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -30,6 +30,34 @@ void pci_ats_init(struct pci_dev *dev)
 	dev->ats_cap = pos;
 }
 
+/**
+ * pci_ats_supported - check if the device can use ATS
+ * @dev: the PCI device
+ *
+ * Returns true if the device supports ATS and is allowed to use it, false
+ * otherwise.
+ */
+bool pci_ats_supported(struct pci_dev *dev)
+{
+	struct pci_host_bridge *bridge;
+
+	if (!dev->ats_cap)
+		return false;
+
+	if (dev->untrusted)
+		return false;
+
+	bridge = pci_find_host_bridge(dev->bus);
+	if (!bridge)
+		return false;
+
+	if (!bridge->ats_supported)
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(pci_ats_supported);
+
 /**
  * pci_enable_ats - enable the ATS capability
  * @dev: the PCI device
@@ -42,7 +70,7 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
 	u16 ctrl;
 	struct pci_dev *pdev;
 
-	if (!dev->ats_cap)
+	if (!pci_ats_supported(dev))
 		return -EINVAL;
 
 	if (WARN_ON(dev->ats_enabled))
diff --git a/include/linux/pci-ats.h b/include/linux/pci-ats.h
index d08f0869f121..f75c307f346d 100644
--- a/include/linux/pci-ats.h
+++ b/include/linux/pci-ats.h
@@ -6,11 +6,14 @@
 
 #ifdef CONFIG_PCI_ATS
 /* Address Translation Service */
+bool pci_ats_supported(struct pci_dev *dev);
 int pci_enable_ats(struct pci_dev *dev, int ps);
 void pci_disable_ats(struct pci_dev *dev);
 int pci_ats_queue_depth(struct pci_dev *dev);
 int pci_ats_page_aligned(struct pci_dev *dev);
 #else /* CONFIG_PCI_ATS */
+static inline bool pci_ats_supported(struct pci_dev *d)
+{ return false; }
 static inline int pci_enable_ats(struct pci_dev *d, int ps)
 { return -ENODEV; }
 static inline void pci_disable_ats(struct pci_dev *d) { }
-- 
2.25.1