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Commit 8c25c0cb authored by Russell King's avatar Russell King Committed by David S. Miller
Browse files

doc: phy: document some PHY_INTERFACE_MODE_xxx settings 



There seems to be some confusion surrounding three PHY interface modes,
specifically 1000BASE-X, 2500BASE-X and SGMII.  Add some documentation
to phylib detailing precisely what these interface modes refer to.

Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: default avatarAndrew Lunn <andrew@lunn.ch>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 08003d0b

Documentation/networking/phy.rst

+44 −1
Original line number Diff line number Diff line
@@ -202,7 +202,8 @@ the PHY/controller, of which the PHY needs to be aware. 


*interface* is a u32 which specifies the connection type used

between the controller and the PHY.  Examples are GMII, MII,

RGMII, and SGMII.  For a full list, see include/linux/phy.h

RGMII, and SGMII.  See "PHY interface mode" below.  For a full

list, see include/linux/phy.h



Now just make sure that phydev->supported and phydev->advertising have any

values pruned from them which don't make sense for your controller (a 10/100
@@ -225,6 +226,48 @@ When you want to disconnect from the network (even if just briefly), you call 
phy_stop(phydev). This function also stops the phylib state machine and

disables PHY interrupts.



PHY interface modes

===================



The PHY interface mode supplied in the phy_connect() family of functions

defines the initial operating mode of the PHY interface.  This is not

guaranteed to remain constant; there are PHYs which dynamically change

their interface mode without software interaction depending on the

negotiation results.



Some of the interface modes are described below:



``PHY_INTERFACE_MODE_1000BASEX``

    This defines the 1000BASE-X single-lane serdes link as defined by the

    802.3 standard section 36.  The link operates at a fixed bit rate of

    1.25Gbaud using a 10B/8B encoding scheme, resulting in an underlying

    data rate of 1Gbps.  Embedded in the data stream is a 16-bit control

    word which is used to negotiate the duplex and pause modes with the

    remote end.  This does not include "up-clocked" variants such as 2.5Gbps

    speeds (see below.)



``PHY_INTERFACE_MODE_2500BASEX``

    This defines a variant of 1000BASE-X which is clocked 2.5 times faster,

    than the 802.3 standard giving a fixed bit rate of 3.125Gbaud.



``PHY_INTERFACE_MODE_SGMII``

    This is used for Cisco SGMII, which is a modification of 1000BASE-X

    as defined by the 802.3 standard.  The SGMII link consists of a single

    serdes lane running at a fixed bit rate of 1.25Gbaud with 10B/8B

    encoding.  The underlying data rate is 1Gbps, with the slower speeds of

    100Mbps and 10Mbps being achieved through replication of each data symbol.

    The 802.3 control word is re-purposed to send the negotiated speed and

    duplex information from to the MAC, and for the MAC to acknowledge

    receipt.  This does not include "up-clocked" variants such as 2.5Gbps

    speeds.



    Note: mismatched SGMII vs 1000BASE-X configuration on a link can

    successfully pass data in some circumstances, but the 16-bit control

    word will not be correctly interpreted, which may cause mismatches in

    duplex, pause or other settings.  This is dependent on the MAC and/or

    PHY behaviour.





Pause frames / flow control

===========================