[Qemu-devel] [PATCH V3 6/8] hw/mdio: Refactor bitbanging state machine

[Grant Likely <grant.likely@secretlab.ca>]

The MDIO state machine has a moderate amount of duplicate code in the
state processing that can be consolidated. This patch does so and
reorganizes it a bit so that far less code is required. Most of the
states simply stream a fixed number of bits in as a single integer and
can be handled by a common processing function that checks for
completion of the state and returns the streamed in value.

Changes include:
- Move clock state change tracking into core code
- Use a common shift register for clocking data in and out
- Create separate mdc & mdio accessor functions
  - will be replaced with GPIO connection in a follow-on patch

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Paul Brook <paul@codesourcery.com>
Cc: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>
Cc: Andreas Färber <afaerber@suse.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
---
 hw/etraxfs_eth.c |   11 ++---
 hw/mdio.c        |  134 ++++++++++++++++++++++--------------------------------
 hw/mdio.h        |   36 ++++++++-------
 3 files changed, 78 insertions(+), 103 deletions(-)

diff --git a/hw/etraxfs_eth.c b/hw/etraxfs_eth.c
index 4d56134..6ff29ea 100644
--- a/hw/etraxfs_eth.c
+++ b/hw/etraxfs_eth.c
@@ -113,7 +113,7 @@ eth_read(void *opaque, hwaddr addr, unsigned int size)
 
     switch (addr) {
     case R_STAT:
-        r = eth->mdio_bus.mdio & 1;
+        r = mdio_bitbang_get_data(&eth->mdio_bus);
         break;
     default:
         r = eth->regs[addr];
@@ -171,13 +171,10 @@ eth_write(void *opaque, hwaddr addr,
     case RW_MGM_CTRL:
         /* Attach an MDIO/PHY abstraction.  */
         if (value & 2) {
-            eth->mdio_bus.mdio = value & 1;
+            mdio_bitbang_set_data(&eth->mdio_bus, value & 1);
         }
-        if (eth->mdio_bus.mdc != (value & 4)) {
-            mdio_cycle(&eth->mdio_bus);
-            eth_validate_duplex(eth);
-        }
-        eth->mdio_bus.mdc = !!(value & 4);
+        mdio_bitbang_set_clk(&eth->mdio_bus, value & 4);
+        eth_validate_duplex(eth);
         eth->regs[addr] = value;
         break;
 
diff --git a/hw/mdio.c b/hw/mdio.c
index 45e271f..79f0e3b 100644
--- a/hw/mdio.c
+++ b/hw/mdio.c
@@ -43,7 +43,7 @@
  * linux driver (PHYID and Diagnostics reg).
  * TODO: Add friendly names for the register nums.
  */
-static unsigned int mdio_phy_read(struct qemu_phy *phy, unsigned int req)
+static uint16_t mdio_phy_read(struct qemu_phy *phy, unsigned int req)
 {
     int regnum;
     unsigned r = 0;
@@ -107,7 +107,7 @@ static unsigned int mdio_phy_read(struct qemu_phy *phy, unsigned int req)
     return r;
 }
 
-static void mdio_phy_write(struct qemu_phy *phy, unsigned int req, unsigned int data)
+static void mdio_phy_write(struct qemu_phy *phy, unsigned int req, uint16_t data)
 {
     int regnum = req & 0x1f;
     uint16_t mask = phy->regs_readonly_mask[regnum];
@@ -136,7 +136,7 @@ void mdio_phy_init(struct qemu_phy *phy, uint16_t id1, uint16_t id2)
     /* Autonegotiation advertisement reg. */
     phy->regs[PHY_AUTONEG_ADV] = 0x01e1;
     phy->regs_readonly_mask = default_readonly_mask;
-    phy->link = 1;
+    phy->link = true;
 
     phy->read = mdio_phy_read;
     phy->write = mdio_phy_write;
@@ -169,99 +169,75 @@ void mdio_write_req(struct qemu_mdio *bus, uint8_t addr, uint8_t req,
     }
 }
 
-void mdio_cycle(struct qemu_mdio *bus)
+/**
+ * mdio_bitbang_update() - internal function to check how many clocks have
+ * passed and move to the next state if necessary. Returns TRUE on state change.
+ */
+static bool mdio_bitbang_update(struct qemu_mdio *bus, int num_bits, int next, uint16_t *reg)
 {
-    bus->cnt++;
+    if (bus->cnt < num_bits) {
+        return false;
+    }
+    if (reg) {
+        *reg = bus->shiftreg;
+    }
+    bus->state = next;
+    bus->cnt = 0;
+    bus->shiftreg = 0;
+    return true;
+}
 
+/**
+ * mdio_bitbang_set_clk() - set value of mdc signal and update state
+ */
+void mdio_bitbang_set_clk(struct qemu_mdio *bus, bool mdc)
+{
+    uint16_t tmp;
+
+    if (mdc == bus->mdc) {
+        return; /* Clock state hasn't changed; do nothing */
+    }
+
+    bus->mdc = mdc;
+    if (bus->mdc) {
+        /* Falling (inactive) clock edge */
+        if ((bus->state == DATA) && (bus->opc == 2)) {
+            bus->mdio = !!(bus->shiftreg & 0x8000);
+        }
+        return;
+    }
+
+    /* Rising clock Edge */
+    bus->shiftreg = (bus->shiftreg << 1) | bus->mdio;
+    bus->cnt++;
     D(printf("mdc=%d mdio=%d state=%d cnt=%d drv=%d\n",
-             bus->mdc, bus->mdio, bus->state, bus->cnt, bus->drive));
+             bus->mdc, bus->mdio, bus->state, bus->cnt));
     switch (bus->state) {
     case PREAMBLE:
-        if (bus->mdc) {
-            if (bus->cnt >= (32 * 2) && !bus->mdio) {
-                bus->cnt = 0;
-                bus->state = SOF;
-                bus->data = 0;
-            }
-        }
-        break;
-    case SOF:
-        if (bus->mdc) {
-            if (bus->mdio != 1) {
-                printf("WARNING: no SOF\n");
-            }
-            if (bus->cnt == 1*2) {
-                bus->cnt = 0;
-                bus->opc = 0;
-                bus->state = OPC;
-            }
+        /* MDIO must be 30 clocks high, 1 low, and 1 high to get out of preamble */
+        if (bus->shiftreg == 0xfffffffd) {
+            mdio_bitbang_update(bus, 0, OPC, NULL);
         }
         break;
     case OPC:
-        if (bus->mdc) {
-            bus->opc <<= 1;
-            bus->opc |= bus->mdio & 1;
-            if (bus->cnt == 2*2) {
-                bus->cnt = 0;
-                bus->addr = 0;
-                bus->state = ADDR;
-            }
-        }
+        mdio_bitbang_update(bus, 2, ADDR, &bus->opc);
         break;
     case ADDR:
-        if (bus->mdc) {
-            bus->addr <<= 1;
-            bus->addr |= bus->mdio & 1;
-
-            if (bus->cnt == 5*2) {
-                bus->cnt = 0;
-                bus->req = 0;
-                bus->state = REQ;
-            }
-        }
+        mdio_bitbang_update(bus, 5, REQ, &bus->addr);
         break;
     case REQ:
-        if (bus->mdc) {
-            bus->req <<= 1;
-            bus->req |= bus->mdio & 1;
-            if (bus->cnt == 5*2) {
-                bus->cnt = 0;
-                bus->state = TURNAROUND;
-            }
-        }
+        mdio_bitbang_update(bus, 5, TURNAROUND, &bus->req);
         break;
     case TURNAROUND:
-        if (bus->mdc && bus->cnt == 2*2) {
-            bus->mdio = 0;
-            bus->cnt = 0;
-
-            if (bus->opc == 2) {
-                bus->drive = 1;
-                bus->data = mdio_read_req(bus, bus->addr, bus->req);
-                bus->mdio = bus->data & 1;
-            }
-            bus->state = DATA;
+        /* If beginning of DATA READ cycle, then read PHY into shift register */
+        if (mdio_bitbang_update(bus, 2, DATA, NULL) && (bus->opc == 2)) {
+            bus->shiftreg = mdio_read_req(bus, bus->addr, bus->req);
         }
         break;
     case DATA:
-        if (!bus->mdc) {
-            if (bus->drive) {
-                bus->mdio = !!(bus->data & (1 << 15));
-                bus->data <<= 1;
-            }
-        } else {
-            if (!bus->drive) {
-                bus->data <<= 1;
-                bus->data |= bus->mdio;
-            }
-            if (bus->cnt == 16 * 2) {
-                bus->cnt = 0;
-                bus->state = PREAMBLE;
-                if (!bus->drive) {
-                    mdio_write_req(bus, bus->addr, bus->req, bus->data);
-                }
-                bus->drive = 0;
-            }
+        /* If end of DATA WRITE cycle, then write shift register to PHY */
+        if (mdio_bitbang_update(bus, 16, PREAMBLE, &tmp) && (bus->opc == 1)) {
+            mdio_write_req(bus, bus->addr, bus->req, tmp);
         }
         break;
     default:
diff --git a/hw/mdio.h b/hw/mdio.h
index 0a6c20a..340501e 100644
--- a/hw/mdio.h
+++ b/hw/mdio.h
@@ -54,37 +54,33 @@
 #define PHY_ADVERTISE_100FULL   0x0100  /* Try for 100mbps full-duplex */
 
 struct qemu_phy {
-    uint32_t regs[NUM_PHY_REGS];
+    uint16_t regs[NUM_PHY_REGS];
     const uint16_t *regs_readonly_mask; /* 0=writable, 1=read-only */
 
-    int link;
+    bool link;
 
-    unsigned int (*read)(struct qemu_phy *phy, unsigned int req);
-    void (*write)(struct qemu_phy *phy, unsigned int req, unsigned int data);
+    uint16_t (*read)(struct qemu_phy *phy, unsigned int req);
+    void (*write)(struct qemu_phy *phy, unsigned int req, uint16_t data);
 };
 
 struct qemu_mdio {
-    /* bus. */
-    int mdc;
-    int mdio;
-
-    /* decoder.  */
+    /* bitbanging state machine */
+    bool mdc;
+    bool mdio;
     enum {
         PREAMBLE,
-        SOF,
         OPC,
         ADDR,
         REQ,
         TURNAROUND,
         DATA
     } state;
-    unsigned int drive;
 
-    unsigned int cnt;
-    unsigned int addr;
-    unsigned int opc;
-    unsigned int req;
-    unsigned int data;
+    uint16_t cnt; /* Bit count for current state */
+    uint16_t addr; /* PHY Address; retrieved during ADDR state */
+    uint16_t opc; /* Operation; 2:read */
+    uint16_t req; /* Register address */
+    uint32_t shiftreg; /* shift register; bits in to or out from PHY */
 
     struct qemu_phy *devs[32];
 };
@@ -94,6 +90,12 @@ void mdio_attach(struct qemu_mdio *bus, struct qemu_phy *phy,
                  unsigned int addr);
 uint16_t mdio_read_req(struct qemu_mdio *bus, uint8_t addr, uint8_t req);
 void mdio_write_req(struct qemu_mdio *bus, uint8_t addr, uint8_t req, uint16_t data);
-void mdio_cycle(struct qemu_mdio *bus);
+void mdio_bitbang_set_clk(struct qemu_mdio *bus, bool mdc);
+static inline void mdio_bitbang_set_data(struct qemu_mdio *bus, bool mdio) {
+    bus->mdio = mdio;
+}
+static inline bool mdio_bitbang_get_data(struct qemu_mdio *bus) {
+    return bus->mdio;
+}
 
 #endif
-- 
1.7.10.4