On Sat, Jul 04, 2020 at 03:45:06PM +0300, Vladimir Oltean wrote: > From: Vladimir Oltean <vladimir.olt...@nxp.com> > > The Cisco SGMII and USXGMII standards specify control information > exchange to be "achieved by using the Auto-Negotiation functionality > defined in Clause 37 of the IEEE Specification 802.3z". > > The differences to clause 37 auto-negotiation are specified by the > respective standards. In the case of SGMII, the differences are spelled > out as being: > > - A reduction of the link timer value, from 10 ms to 1.6 ms. > - A customization of the tx_config_reg[15:0], mostly to allow > propagation of speed information. > > A similar situation is going on for USXGMII as well: "USXGMII Auto-neg > mechanism is based on Clause 37 (Figure 37-6) plus additional management > control to select USXGMII mode". > > The point is, both Cisco standards make explicit reference that they > require an auto-negotiation state machine implemented as per "Figure > 37-6-Auto-Negotiation state diagram" from IEEE 802.3. In the SGMII spec, > it is very clearly pointed out that both the MAC PCS (Figure 3 MAC > Functional Block) and the PHY PCS (Figure 2 PHY Functional Block) > contain an auto-negotiation block defined by "Auto-Negotiation Figure > 37-6". > > Since both ends of the SGMII/USXGMII link implement the same state > machine (just carry different tx_config_reg payloads, which they convey > to their link partner via /C/ ordered sets), naturally the ability to > restart auto-negotiation is symmetrical. The state machine in IEEE 802.3 > Figure 37-6 specifies the signal that triggers an auto-negotiation > restart as being "mr_restart_an=TRUE". > > Furthermore, clause "37.2.5.1.9 State diagram variable to management > register mapping", through its "Table 37-8-PCS state diagram variable to > management register mapping", requires a PCS compliant to clause 37 to > expose the mr_restart_an signal to management through MDIO register "0.9 > Auto-Negotiation restart", aka BMCR_ANRESTART in Linux terms. > > The Felix PCS for SGMII and USXGMII is compliant to clause 37, so it > exposes BMCR_ANRESTART to the operating system. When this bit is > asserted, the following happens: > > 1. STATUS[Auto_Negotiation_Complete] goes from 1->0. > 2. The PCS starts sending AN sequences instead of packets or IDLEs. > 3. The PCS waits to receive AN sequences from PHY and matches them. > 4. Once it has received matching AN sequences and a PHY acknowledge, > STATUS[Auto_Negotiation_Complete] goes from 0->1. > 5. Normal packet transmission restarts. > > Otherwise stated, the MAC PCS has the ability to re-trigger a switch of > the lane from data mode into configuration mode, then control > information exchange takes place, then the lane is switched back into > data mode. These 5 steps are collectively described as "restart AN state > machine" by the PCS documentation. > This is all as per IEEE 802.3 Clause 37 AN state machine, which SGMII > and USXGMII do not touch at this fundamental level. > > Now, it is true that the Cisco SGMII and USXGMII specs mention that the > control information exchange has a unidirectional meaning. That is, the > PHY restarts the clause 37 auto-negotiation upon any change in MDI > auto-negotiation parameters. > > PHYLINK takes this fact a bit further, and since the fact that for > SGMII/USXGMII, the MAC PCS conveys no new information to the PHY PCS > (beyond acknowledging the received config word), does not have any use > for permitting the MAC PCS to trigger a restart of the clause 37 > auto-negotiation. > > The only SERDES protocols for which PHYLINK allows that are 1000Base-X > and 2500Base-X. For those, the control information exchange _is_ > bidirectional (local PCS specifies its duplex and flow control > abilities) since the link partner is at the other side of the media. > > For any other SERDES protocols, the .phylink_mac_an_restart callback is > dead code. This is probably OK, I can't come up with a situation where > it might be useful for the MAC PCS to clear its cache of link state and > ask for a new tx_config_reg. > > So remove this code.
NAK for this description. You know why. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
