60 lines
2.9 KiB
Text
60 lines
2.9 KiB
Text
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Switch (and switch-ish) device drivers HOWTO
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===========================
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Please note that the word "switch" is here used in very generic meaning.
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This include devices supporting L2/L3 but also various flow offloading chips,
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including switches embedded into SR-IOV NICs.
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Lets describe a topology a bit. Imagine the following example:
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+----------------------------+ +---------------+
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| SOME switch chip | | CPU |
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+----------------------------+ +---------------+
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port1 port2 port3 port4 MNGMNT | PCI-E |
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| | | | | +---------------+
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PHY PHY | | | | NIC0 NIC1
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| | | | | |
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| | +- PCI-E -+ | |
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| +------- MII -------+ |
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+------------- MII ------------+
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In this example, there are two independent lines between the switch silicon
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and CPU. NIC0 and NIC1 drivers are not aware of a switch presence. They are
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separate from the switch driver. SOME switch chip is by managed by a driver
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via PCI-E device MNGMNT. Note that MNGMNT device, NIC0 and NIC1 may be
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connected to some other type of bus.
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Now, for the previous example show the representation in kernel:
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+----------------------------+ +---------------+
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| SOME switch chip | | CPU |
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+----------------------------+ +---------------+
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sw0p0 sw0p1 sw0p2 sw0p3 MNGMNT | PCI-E |
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| | | | | +---------------+
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PHY PHY | | | | eth0 eth1
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| | | | | |
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| | +- PCI-E -+ | |
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| +------- MII -------+ |
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+------------- MII ------------+
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Lets call the example switch driver for SOME switch chip "SOMEswitch". This
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driver takes care of PCI-E device MNGMNT. There is a netdevice instance sw0pX
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created for each port of a switch. These netdevices are instances
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of "SOMEswitch" driver. sw0pX netdevices serve as a "representation"
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of the switch chip. eth0 and eth1 are instances of some other existing driver.
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The only difference of the switch-port netdevice from the ordinary netdevice
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is that is implements couple more NDOs:
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ndo_switch_parent_id_get - This returns the same ID for two port netdevices
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of the same physical switch chip. This is
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mandatory to be implemented by all switch drivers
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and serves the caller for recognition of a port
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netdevice.
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ndo_switch_parent_* - Functions that serve for a manipulation of the switch
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chip itself (it can be though of as a "parent" of the
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port, therefore the name). They are not port-specific.
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Caller might use arbitrary port netdevice of the same
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switch and it will make no difference.
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ndo_switch_port_* - Functions that serve for a port-specific manipulation.
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