hw/net/cadence_gem: perform PHY access on write only

The MDIO access is done only on a write to the PHYMNTNC register. A
subsequent read is used to retrieve the result but does not trigger an
MDIO access by itself.

Refactor the PHY access logic to perform all accesses (MDIO reads and
writes) at PHYMNTNC write time.

Signed-off-by: Luc Michel <luc.michel@amd.com>
Reviewed-by: sai.pavan.boddu@amd.com
Message-id: 20231017194422.4124691-11-luc.michel@amd.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/net/cadence_gem.c

@@ -1521,6 +1521,38 @@ static void gem_phy_write(CadenceGEMState *s, unsigned reg_num, uint16_t val)
     s->phy_regs[reg_num] = val;
 }
 
+static void gem_handle_phy_access(CadenceGEMState *s)
+{
+    uint32_t val = s->regs[R_PHYMNTNC];
+    uint32_t phy_addr, reg_num;
+
+    phy_addr = FIELD_EX32(val, PHYMNTNC, PHY_ADDR);
+
+    if (phy_addr != s->phy_addr) {
+        /* no phy at this address */
+        if (FIELD_EX32(val, PHYMNTNC, OP) == MDIO_OP_READ) {
+            s->regs[R_PHYMNTNC] = FIELD_DP32(val, PHYMNTNC, DATA, 0xffff);
+        }
+        return;
+    }
+
+    reg_num = FIELD_EX32(val, PHYMNTNC, REG_ADDR);
+
+    switch (FIELD_EX32(val, PHYMNTNC, OP)) {
+    case MDIO_OP_READ:
+        s->regs[R_PHYMNTNC] = FIELD_DP32(val, PHYMNTNC, DATA,
+                                         gem_phy_read(s, reg_num));
+        break;
+
+    case MDIO_OP_WRITE:
+        gem_phy_write(s, reg_num, val);
+        break;
+
+    default:
+        break; /* only clause 22 operations are supported */
+    }
+}
+
 /*
  * gem_read32:
  * Read a GEM register.
@@ -1541,20 +1573,6 @@ static uint64_t gem_read(void *opaque, hwaddr offset, unsigned size)
         DB_PRINT("lowering irqs on ISR read\n");
         /* The interrupts get updated at the end of the function. */
         break;
-    case R_PHYMNTNC:
-        if (FIELD_EX32(retval, PHYMNTNC, OP) == MDIO_OP_READ) {
-            uint32_t phy_addr, reg_num;
-
-            phy_addr = FIELD_EX32(retval, PHYMNTNC, PHY_ADDR);
-            if (phy_addr == s->phy_addr) {
-                reg_num = FIELD_EX32(retval, PHYMNTNC, REG_ADDR);
-                retval &= 0xFFFF0000;
-                retval |= gem_phy_read(s, reg_num);
-            } else {
-                retval |= 0xFFFF; /* No device at this address */
-            }
-        }
-        break;
     }
 
     /* Squash read to clear bits */
@@ -1665,15 +1683,7 @@ static void gem_write(void *opaque, hwaddr offset, uint64_t val,
         s->sar_active[(offset - R_SPADDR1HI) / 2] = true;
         break;
     case R_PHYMNTNC:
-        if (FIELD_EX32(val, PHYMNTNC, OP) == MDIO_OP_WRITE) {
-            uint32_t phy_addr, reg_num;
-
-            phy_addr = FIELD_EX32(val, PHYMNTNC, PHY_ADDR);
-            if (phy_addr == s->phy_addr) {
-                reg_num = FIELD_EX32(val, PHYMNTNC, REG_ADDR);
-                gem_phy_write(s, reg_num, val);
-            }
-        }
+        gem_handle_phy_access(s);
         break;
     }