mac_config() can be called at any point, and the expected behaviour
from MAC drivers is to only reprogram when necessary - and certainly
avoid taking the link down on every call.
Unfortunately, mvpp2 does exactly that - it takes the link down, and
reprograms everything, and then releases the forced-link down.
This is bad, it can cause the link to bounce:
- SFP detects signal, disables LOS indication.
- SFP code calls into phylink, calling phylink_sfp_link_up() which
triggers a resolve.
- phylink_resolve() calls phylink_get_mac_state() and finds the MAC
reporting link up.
- phylink wants to configure the pause mode on the MAC, so calls
phylink_mac_config()
- mvpp2 takes the link down temporarily, generating a MAC link down
event followed by another MAC link event.
- phylink calls mac_link_up() and then processes the MAC link down
event.
- phylink_resolve() gets called again, registers the link down, and
calls mach_link_down() before re-running itself.
- phylink_resolve() starts again at step 3 above. This sequence
repeats.
GMAC versions prior to mvpp2 do not require the link to be taken down
except when certain link properties (eg, switching between SGMII and
1000base-X mode, or enabling/disabling in-band negotiation) are
changed. Implement this for mvpp2.
Tested-by: Sven Auhagen <sven.auhagen@voleatech.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
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