Here is the list of the MAC capabilities specific to the particular DW MAC
IP-cores currently supported by the driver:

DW MAC100: MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
	   MAC_10 | MAC_100

DW GMAC:  MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
          MAC_10 | MAC_100 | MAC_1000

Allwinner sun8i MAC: MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
                     MAC_10 | MAC_100 | MAC_1000

DW QoS Eth: MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
            MAC_10 | MAC_100 | MAC_1000 | MAC_2500FD
if there is more than 1 active Tx/Rx queues:
	   MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
           MAC_10FD | MAC_100FD | MAC_1000FD | MAC_2500FD

DW XGMAC: MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
          MAC_1000FD | MAC_2500FD | MAC_5000FD | MAC_10000FD

DW XLGMAC: MAC_ASYM_PAUSE | MAC_SYM_PAUSE |
          MAC_1000FD | MAC_2500FD | MAC_5000FD | MAC_10000FD |
          MAC_25000FD | MAC_40000FD | MAC_50000FD | MAC_100000FD

As you can see there are only two common capabilities:
MAC_ASYM_PAUSE | MAC_SYM_PAUSE.
Meanwhile what is currently implemented defines 10/100/1000 link speeds
for all IP-cores, which is definitely incorrect for DW MAC100, DW XGMAC
and DW XLGMAC devices.

Seeing the flow-control is implemented as a callback for each MAC IP-core
(see dwmac100_flow_ctrl(), dwmac1000_flow_ctrl(), sun8i_dwmac_flow_ctrl(),
etc) and since the MAC-specific setup() method is supposed to be called
for each available DW MAC-based device, the capabilities initialization
can be freely moved to these setup() functions, thus correctly setting up
the MAC-capabilities for each IP-core (including the Allwinner Sun8i). A
new stmmac_link::caps field was specifically introduced for that so to
have all link-specific info preserved in a single structure.

Note the suggested change fixes three earlier commits at a time. The
commit 5b0d7d7d ("net: stmmac: Add the missing speeds that XGMAC
supports") permitted the 10-100 link speeds and 1G half-duplex mode for DW
XGMAC IP-core even though it doesn't support them. The commit df7699c7
("net: stmmac: Do not cut down 1G modes") incorrectly added the MAC1000
capability to the DW MAC100 IP-core. Similarly to the DW XGMAC the commit
8a880936 ("net: stmmac: Add XLGMII support") incorrectly permitted the
10-100 link speeds and 1G half-duplex mode for DW XLGMAC IP-core.

Fixes: 5b0d7d7d ("net: stmmac: Add the missing speeds that XGMAC supports")
Fixes: df7699c7 ("net: stmmac: Do not cut down 1G modes")
Fixes: 8a880936 ("net: stmmac: Add XLGMII support")
Suggested-by: Russell King (Oracle) <linux@armlinux.org.uk>
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Romain Gantois <romain.gantois@bootlin.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>