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Subject[PATCH v5 03/14] PCI: Add pcie_bandwidth_capable() to compute max supported link bandwidth
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From: Tal Gilboa <talgi@mellanox.com>

Add pcie_bandwidth_capable() to compute the max link bandwidth supported by
a device, based on the max link speed and width, adjusted by the encoding
overhead.

The maximum bandwidth of the link is computed as:

max_link_speed * max_link_width * (1 - encoding_overhead)

The encoding overhead is about 20% for 2.5 and 5.0 GT/s links using 8b/10b
encoding, and about 1.5% for 8 GT/s or higher speed links using 128b/130b
encoding.

Signed-off-by: Tal Gilboa <talgi@mellanox.com>
[bhelgaas: adjust for pcie_get_speed_cap() and pcie_get_width_cap()
signatures, don't export outside drivers/pci]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
---
drivers/pci/pci.c | 21 +++++++++++++++++++++
drivers/pci/pci.h | 9 +++++++++
2 files changed, 30 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 43075be79388..9ce89e254197 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5208,6 +5208,27 @@ enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev)
return PCIE_LNK_WIDTH_UNKNOWN;
}

+/**
+ * pcie_bandwidth_capable - calculates a PCI device's link bandwidth capability
+ * @dev: PCI device
+ * @speed: storage for link speed
+ * @width: storage for link width
+ *
+ * Calculate a PCI device's link bandwidth by querying for its link speed
+ * and width, multiplying them, and applying encoding overhead.
+ */
+u32 pcie_bandwidth_capable(struct pci_dev *dev, enum pci_bus_speed *speed,
+ enum pcie_link_width *width)
+{
+ *speed = pcie_get_speed_cap(dev);
+ *width = pcie_get_width_cap(dev);
+
+ if (*speed == PCI_SPEED_UNKNOWN || *width == PCIE_LNK_WIDTH_UNKNOWN)
+ return 0;
+
+ return *width * PCIE_SPEED2MBS_ENC(*speed);
+}
+
/**
* pci_select_bars - Make BAR mask from the type of resource
* @dev: the PCI device for which BAR mask is made
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 66738f1050c0..2a50172b9803 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -261,8 +261,17 @@ void pci_disable_bridge_window(struct pci_dev *dev);
(speed) == PCIE_SPEED_2_5GT ? "2.5 GT/s" : \
"Unknown speed")

+/* PCIe speed to Mb/s with encoding overhead: 20% for gen2, ~1.5% for gen3 */
+#define PCIE_SPEED2MBS_ENC(speed) \
+ ((speed) == PCIE_SPEED_8_0GT ? 7877 : \
+ (speed) == PCIE_SPEED_5_0GT ? 4000 : \
+ (speed) == PCIE_SPEED_2_5GT ? 2000 : \
+ 0)
+
enum pci_bus_speed pcie_get_speed_cap(struct pci_dev *dev);
enum pcie_link_width pcie_get_width_cap(struct pci_dev *dev);
+u32 pcie_bandwidth_capable(struct pci_dev *dev, enum pci_bus_speed *speed,
+ enum pcie_link_width *width);

/* Single Root I/O Virtualization */
struct pci_sriov {
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