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authorJiri Pirko <jiri@resnulli.us>2014-11-28 14:34:17 +0100
committerDavid S. Miller <davem@davemloft.net>2014-12-02 20:01:20 -0800
commit007f790c8276271de26416f90d55561bcc96588a (patch)
tree03a55b7897402e9daa8af64ea2c81d5236f77367 /Documentation/networking
parent02637fce3e0103ba086b9c33b6d529e69460e4b6 (diff)
downloadkernel-007f790c8276271de26416f90d55561bcc96588a.tar.gz
net: introduce generic switch devices support
The goal of this is to provide a possibility to support various switch chips. Drivers should implement relevant ndos to do so. Now there is only one ndo defined: - for getting physical switch id is in place. Note that user can use random port netdevice to access the switch. Signed-off-by: Jiri Pirko <jiri@resnulli.us> Reviewed-by: Thomas Graf <tgraf@suug.ch> Acked-by: Andy Gospodarek <gospo@cumulusnetworks.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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+Switch (and switch-ish) device drivers HOWTO
+===========================
+
+Please note that the word "switch" is here used in very generic meaning.
+This include devices supporting L2/L3 but also various flow offloading chips,
+including switches embedded into SR-IOV NICs.
+
+Lets describe a topology a bit. Imagine the following example:
+
+ +----------------------------+ +---------------+
+ | SOME switch chip | | CPU |
+ +----------------------------+ +---------------+
+ port1 port2 port3 port4 MNGMNT | PCI-E |
+ | | | | | +---------------+
+ PHY PHY | | | | NIC0 NIC1
+ | | | | | |
+ | | +- PCI-E -+ | |
+ | +------- MII -------+ |
+ +------------- MII ------------+
+
+In this example, there are two independent lines between the switch silicon
+and CPU. NIC0 and NIC1 drivers are not aware of a switch presence. They are
+separate from the switch driver. SOME switch chip is by managed by a driver
+via PCI-E device MNGMNT. Note that MNGMNT device, NIC0 and NIC1 may be
+connected to some other type of bus.
+
+Now, for the previous example show the representation in kernel:
+
+ +----------------------------+ +---------------+
+ | SOME switch chip | | CPU |
+ +----------------------------+ +---------------+
+ sw0p0 sw0p1 sw0p2 sw0p3 MNGMNT | PCI-E |
+ | | | | | +---------------+
+ PHY PHY | | | | eth0 eth1
+ | | | | | |
+ | | +- PCI-E -+ | |
+ | +------- MII -------+ |
+ +------------- MII ------------+
+
+Lets call the example switch driver for SOME switch chip "SOMEswitch". This
+driver takes care of PCI-E device MNGMNT. There is a netdevice instance sw0pX
+created for each port of a switch. These netdevices are instances
+of "SOMEswitch" driver. sw0pX netdevices serve as a "representation"
+of the switch chip. eth0 and eth1 are instances of some other existing driver.
+
+The only difference of the switch-port netdevice from the ordinary netdevice
+is that is implements couple more NDOs:
+
+ ndo_switch_parent_id_get - This returns the same ID for two port netdevices
+ of the same physical switch chip. This is
+ mandatory to be implemented by all switch drivers
+ and serves the caller for recognition of a port
+ netdevice.
+ ndo_switch_parent_* - Functions that serve for a manipulation of the switch
+ chip itself (it can be though of as a "parent" of the
+ port, therefore the name). They are not port-specific.
+ Caller might use arbitrary port netdevice of the same
+ switch and it will make no difference.
+ ndo_switch_port_* - Functions that serve for a port-specific manipulation.