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PCI: Add pcie_bandwidth_available() to compute bandwidth available to device

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Add pcie_bandwidth_available() to compute the bandwidth available to a
device.  This may be limited by the device itself or by a slower upstream
link leading to the device.

The available bandwidth at each link along the path is computed as:

  link_width * 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.

Also return the device with the slowest link and the speed and width of
that link.

Signed-off-by: Tal Gilboa <talgi@mellanox.com>
[bhelgaas: changelog, leave pcie_get_minimum_link() alone for now, return
bw directly, use pci_upstream_bridge(), check "next_bw <= bw" to find
uppermost limiting device, return speed/width of the limiting device]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
This commit is contained in:
Tal Gilboa 2018-03-30 08:37:44 -05:00 committed by Bjorn Helgaas
parent b852f63aa6
commit 6db79a88c6
2 changed files with 61 additions and 0 deletions
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58
drivers/pci/pci.c
View File

@ -5146,6 +5146,64 @@ int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
}
EXPORT_SYMBOL(pcie_get_minimum_link);
/**
* pcie_bandwidth_available - determine minimum link settings of a PCIe
* device and its bandwidth limitation
* @dev: PCI device to query
* @limiting_dev: storage for device causing the bandwidth limitation
* @speed: storage for speed of limiting device
* @width: storage for width of limiting device
*
* Walk up the PCI device chain and find the point where the minimum
* bandwidth is available. Return the bandwidth available there and (if
* limiting_dev, speed, and width pointers are supplied) information about
* that point. The bandwidth returned is in Mb/s, i.e., megabits/second of
* raw bandwidth.
*/
u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev **limiting_dev,
enum pci_bus_speed *speed,
enum pcie_link_width *width)
{
u16 lnksta;
enum pci_bus_speed next_speed;
enum pcie_link_width next_width;
u32 bw, next_bw;
if (speed)
*speed = PCI_SPEED_UNKNOWN;
if (width)
*width = PCIE_LNK_WIDTH_UNKNOWN;
bw = 0;
while (dev) {
pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
next_speed = pcie_link_speed[lnksta & PCI_EXP_LNKSTA_CLS];
next_width = (lnksta & PCI_EXP_LNKSTA_NLW) >>
PCI_EXP_LNKSTA_NLW_SHIFT;
next_bw = next_width * PCIE_SPEED2MBS_ENC(next_speed);
/* Check if current device limits the total bandwidth */
if (!bw || next_bw <= bw) {
bw = next_bw;
if (limiting_dev)
*limiting_dev = dev;
if (speed)
*speed = next_speed;
if (width)
*width = next_width;
}
dev = pci_upstream_bridge(dev);
}
return bw;
}
EXPORT_SYMBOL(pcie_bandwidth_available);
/**
* pcie_get_speed_cap - query for the PCI device's link speed capability
* @dev: PCI device to query

3
include/linux/pci.h
View File

@ -1083,6 +1083,9 @@ int pcie_get_mps(struct pci_dev *dev);
int pcie_set_mps(struct pci_dev *dev, int mps);
int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
enum pcie_link_width *width);
u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev **limiting_dev,
enum pci_bus_speed *speed,
enum pcie_link_width *width);
void pcie_flr(struct pci_dev *dev);
int __pci_reset_function_locked(struct pci_dev *dev);
int pci_reset_function(struct pci_dev *dev);