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PCI: Add pcie_bandwidth_capable() to compute max supported link bandwidth

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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_width * max_link_speed * (1 - encoding_overhead)

2.5 and 5.0 GT/s links use 8b/10b encoding, which reduces the raw bandwidth
available by 20%; 8.0 GT/s and faster links use 128b/130b encoding, which
reduces it by about 1.5%.

The result is in Mb/s, i.e., megabits/second, of raw bandwidth.

Signed-off-by: Tal Gilboa <talgi@mellanox.com>
[bhelgaas: add 16 GT/s, 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>
This commit is contained in:
Tal Gilboa
2018-03-30 08:32:03 -05:00
committed by Bjorn Helgaas
parent c70b65fb7f
commit b852f63aa6
2 changed files with 32 additions and 0 deletions
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10
drivers/pci/pci.h
View File

@@ -261,8 +261,18 @@ 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 reduced by encoding overhead */
#define PCIE_SPEED2MBS_ENC(speed) \
((speed) == PCIE_SPEED_16_0GT ? 16000*128/130 : \
(speed) == PCIE_SPEED_8_0GT ? 8000*128/130 : \
(speed) == PCIE_SPEED_5_0GT ? 5000*8/10 : \
(speed) == PCIE_SPEED_2_5GT ? 2500*8/10 : \
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 {