e1000: emulate auto-negotiation during external link status change

This patch emulates auto-negotiation when the network link status
is modified externally (i.e. via "set_link <id> off/on").

Also, a couple of cleanup items:
  - unset PHY status reg. AUTONEG_COMPLETE during link_down()
  - set PHY status reg. AUTONEG_COMPLETE during autoneg_timer() only
    if we actually brought the link up.
  - group all checks for "can we, and should we autonegotiate?"
    together for more clarity.
Signed-off-by: NGabriel Somlo <somlo@cmu.edu>
Reviewed-by: NAlexander Graf <agraf@suse.de>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/net/e1000.c

@@ -175,6 +175,7 @@ e1000_link_down(E1000State *s)
 {
     s->mac_reg[STATUS] &= ~E1000_STATUS_LU;
     s->phy_reg[PHY_STATUS] &= ~MII_SR_LINK_STATUS;
+    s->phy_reg[PHY_STATUS] &= ~MII_SR_AUTONEG_COMPLETE;
 }
 
 static void
@@ -197,7 +198,6 @@ set_phy_ctrl(E1000State *s, int index, uint16_t val)
     }
     if ((val & MII_CR_AUTO_NEG_EN) && (val & MII_CR_RESTART_AUTO_NEG)) {
         e1000_link_down(s);
-        s->phy_reg[PHY_STATUS] &= ~MII_SR_AUTONEG_COMPLETE;
         DBGOUT(PHY, "Start link auto negotiation\n");
         timer_mod(s->autoneg_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 500);
     }
@@ -209,9 +209,9 @@ e1000_autoneg_timer(void *opaque)
     E1000State *s = opaque;
     if (!qemu_get_queue(s->nic)->link_down) {
         e1000_link_up(s);
+        s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
+        DBGOUT(PHY, "Auto negotiation is completed\n");
     }
-    s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
-    DBGOUT(PHY, "Auto negotiation is completed\n");
 }
 
 static void (*phyreg_writeops[])(E1000State *, int, uint16_t) = {
@@ -853,7 +853,16 @@ e1000_set_link_status(NetClientState *nc)
     if (nc->link_down) {
         e1000_link_down(s);
     } else {
-        e1000_link_up(s);
+        if (s->compat_flags & E1000_FLAG_AUTONEG &&
+            s->phy_reg[PHY_CTRL] & MII_CR_AUTO_NEG_EN &&
+            s->phy_reg[PHY_CTRL] & MII_CR_RESTART_AUTO_NEG &&
+            !(s->phy_reg[PHY_STATUS] & MII_SR_AUTONEG_COMPLETE)) {
+            /* emulate auto-negotiation if supported */
+            timer_mod(s->autoneg_timer,
+                      qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + 500);
+        } else {
+            e1000_link_up(s);
+        }
     }
 
     if (s->mac_reg[STATUS] != old_status)
@@ -1279,16 +1288,13 @@ static void e1000_pre_save(void *opaque)
         e1000_mit_timer(s);
     }
 
-    if (!(s->compat_flags & E1000_FLAG_AUTONEG)) {
-        return;
-    }
-
     /*
-     * If link is down and auto-negotiation is ongoing, complete
-     * auto-negotiation immediately.  This allows is to look at
-     * MII_SR_AUTONEG_COMPLETE to infer link status on load.
+     * If link is down and auto-negotiation is supported and ongoing,
+     * complete auto-negotiation immediately. This allows us to look
+     * at MII_SR_AUTONEG_COMPLETE to infer link status on load.
      */
     if (nc->link_down &&
+        s->compat_flags & E1000_FLAG_AUTONEG &&
         s->phy_reg[PHY_CTRL] & MII_CR_AUTO_NEG_EN &&
         s->phy_reg[PHY_CTRL] & MII_CR_RESTART_AUTO_NEG) {
          s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
@@ -1313,11 +1319,8 @@ static int e1000_post_load(void *opaque, int version_id)
      * Alternatively, restart link negotiation if it was in progress. */
     nc->link_down = (s->mac_reg[STATUS] & E1000_STATUS_LU) == 0;
 
-    if (!(s->compat_flags & E1000_FLAG_AUTONEG)) {
-        return 0;
-    }
-
-    if (s->phy_reg[PHY_CTRL] & MII_CR_AUTO_NEG_EN &&
+    if (s->compat_flags & E1000_FLAG_AUTONEG &&
+        s->phy_reg[PHY_CTRL] & MII_CR_AUTO_NEG_EN &&
         s->phy_reg[PHY_CTRL] & MII_CR_RESTART_AUTO_NEG &&
         !(s->phy_reg[PHY_STATUS] & MII_SR_AUTONEG_COMPLETE)) {
         nc->link_down = false;