net: mtk_eth_soc: add fixme comment for state->speed use

Add a fixme comment for the last remaining incorrect usage of
state->speed in the mac_config() method, which is strangely in a code
path which is only run when the PHY interface mode changes.

This means if we are in RGMII mode, changes in state->speed will not
cause the INTF_MODE, TRGMII_RCK_CTRL and TRGMII_TCK_CTRL registers to
be set according to the speed, nor will the TRGPLL clock be set to the
correct value.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -327,6 +327,14 @@ static void mtk_mac_config(struct phylink_config *config, unsigned int mode,
 							      state->interface))
 					goto err_phy;
 			} else {
+				/* FIXME: this is incorrect. Not only does it
+				 * use state->speed (which is not guaranteed
+				 * to be correct) but it also makes use of it
+				 * in a code path that will only be reachable
+				 * when the PHY interface mode changes, not
+				 * when the speed changes. Consequently, RGMII
+				 * is probably broken.
+				 */
 				mtk_gmac0_rgmii_adjust(mac->hw,
 						       state->interface,
 						       state->speed);