phylib: Fix auto-negotiation restart avoidance

A previous patch, 51e2a3846eab18711f4eb59cd0a4c33054e2980a, made
genphy_config_aneg() not restart aneg by calling genphy_restart_aneg() if
the advertisement hadn't changed.

But, genphy_restart_aneg() doesn't just restart aneg, it may also *enable*
aneg or un-isolate the PHY from the MII (those functions are controlled by
the same register).  The code to avoid calling genphy_restart_aneg() didn't
consider this.

So, modify genphy_config_aneg() to also check if the PHY needs to have aneg
enabled or be un-isolated before deciding not to restart aneg.

This caused a problem with certain Davicom PHYs, as that driver isolates
the PHY (why?) before calling genphy_config_aneg() and expects the PHY to
be un-isolated by that function.

Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Reported-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 11 deletions

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 8fb1faca883a..55bc24b234e3 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -564,20 +564,32 @@ EXPORT_SYMBOL(genphy_restart_aneg);
  */
 int genphy_config_aneg(struct phy_device *phydev)
 {
-        int result = 0;
+        int result;
 
-        if (AUTONEG_ENABLE == phydev->autoneg) {
-                int result = genphy_config_advert(phydev);
+        if (AUTONEG_ENABLE != phydev->autoneg)
+                return genphy_setup_forced(phydev);
+
+        result = genphy_config_advert(phydev);
+
+        if (result < 0) /* error */
+                return result;
 
-                if (result < 0) /* error */
-                        return result;
+        if (result == 0) {
+                /* Advertisment hasn't changed, but maybe aneg was never on to
+                 * begin with?  Or maybe phy was isolated? */
+                int ctl = phy_read(phydev, MII_BMCR);
+
+                if (ctl < 0)
+                        return ctl;
+
+                if (!(ctl & BMCR_ANENABLE) || (ctl & BMCR_ISOLATE))
+                        result = 1; /* do restart aneg */
+        }
 
-                /* Only restart aneg if we are advertising something different
-                 * than we were before.  */
-                if (result > 0)
-                        result = genphy_restart_aneg(phydev);
-        } else
-                result = genphy_setup_forced(phydev);
+        /* Only restart aneg if we are advertising something different
+         * than we were before.  */
+        if (result > 0)
+                result = genphy_restart_aneg(phydev);
 
         return result;
 }