net: sfp: avoid power switch on address-change modules

If the module indicates that it requires an address change sequence to
switch between address 0x50 and 0x51, which we don't support, we can't
write to the register that controls the power mode to switch to high
power mode.  Warn the user that the module may not be functional in
this case, and don't try to change the power mode.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/sfp.c

@@ -1385,25 +1385,34 @@ static int sfp_module_parse_power(struct sfp *sfp)
 	if (sfp->id.ext.options & cpu_to_be16(SFP_OPTIONS_HIGH_POWER_LEVEL))
 		power_mW = 2000;
 
-	if (sfp->id.ext.sff8472_compliance == SFP_SFF8472_COMPLIANCE_NONE &&
-	    (sfp->id.ext.diagmon & (SFP_DIAGMON_DDM | SFP_DIAGMON_ADDRMODE)) !=
-	    SFP_DIAGMON_DDM) {
-		/* The module appears not to implement bus address 0xa2,
-		 * or requires an address change sequence, so assume that
-		 * the module powers up in the indicated power mode.
-		 */
-		if (power_mW > sfp->max_power_mW) {
+	if (power_mW > sfp->max_power_mW) {
+		/* Module power specification exceeds the allowed maximum. */
+		if (sfp->id.ext.sff8472_compliance ==
+			SFP_SFF8472_COMPLIANCE_NONE &&
+		    !(sfp->id.ext.diagmon & SFP_DIAGMON_DDM)) {
+			/* The module appears not to implement bus address
+			 * 0xa2, so assume that the module powers up in the
+			 * indicated mode.
+			 */
 			dev_err(sfp->dev,
 				"Host does not support %u.%uW modules\n",
 				power_mW / 1000, (power_mW / 100) % 10);
 			return -EINVAL;
+		} else {
+			dev_warn(sfp->dev,
+				 "Host does not support %u.%uW modules, module left in power mode 1\n",
+				 power_mW / 1000, (power_mW / 100) % 10);
+			return 0;
 		}
-		return 0;
 	}
 
-	if (power_mW > sfp->max_power_mW) {
+	/* If the module requires a higher power mode, but also requires
+	 * an address change sequence, warn the user that the module may
+	 * not be functional.
+	 */
+	if (sfp->id.ext.diagmon & SFP_DIAGMON_ADDRMODE && power_mW > 1000) {
 		dev_warn(sfp->dev,
-			 "Host does not support %u.%uW modules, module left in power mode 1\n",
+			 "Address Change Sequence not supported but module requies %u.%uW, module may not be functional\n",
 			 power_mW / 1000, (power_mW / 100) % 10);
 		return 0;
 	}