hw/block/pflash_cfi02: Add helpers to manipulate the status bits

Pull out all of the code to modify the status into simple helper
functions. Status handling becomes more complex once multiple
chips are interleaved to produce a single device.

No change in functionality is intended with this commit.
Signed-off-by: NStephen Checkoway <stephen.checkoway@oberlin.edu>
Message-Id: <20190426162624.55977-3-stephen.checkoway@oberlin.edu>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
[PMD: Extracted from bigger patch]
Reviewed-by: NAlistair Francis <alistair.francis@wdc.com>
Signed-off-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>

hw/block/pflash_cfi02.c

@@ -101,6 +101,31 @@ struct PFlashCFI02 {
     void *storage;
 };
 
+/*
+ * Toggle status bit DQ7.
+ */
+static inline void toggle_dq7(PFlashCFI02 *pfl)
+{
+    pfl->status ^= 0x80;
+}
+
+/*
+ * Set status bit DQ7 to bit 7 of value.
+ */
+static inline void set_dq7(PFlashCFI02 *pfl, uint8_t value)
+{
+    pfl->status &= 0x7F;
+    pfl->status |= value & 0x80;
+}
+
+/*
+ * Toggle status bit DQ6.
+ */
+static inline void toggle_dq6(PFlashCFI02 *pfl)
+{
+    pfl->status ^= 0x40;
+}
+
 /*
  * Set up replicated mappings of the same region.
  */
@@ -130,7 +155,7 @@ static void pflash_timer (void *opaque)
 
     trace_pflash_timer_expired(pfl->cmd);
     /* Reset flash */
-    pfl->status ^= 0x80;
+    toggle_dq7(pfl);
     if (pfl->bypass) {
         pfl->wcycle = 2;
     } else {
@@ -229,8 +254,7 @@ static uint32_t pflash_read(PFlashCFI02 *pfl, hwaddr offset,
         /* Status register read */
         ret = pfl->status;
         DPRINTF("%s: status %" PRIx32 "\n", __func__, ret);
-        /* Toggle bit 6 */
-        pfl->status ^= 0x40;
+        toggle_dq6(pfl);
         break;
     case 0x98:
         /* CFI query mode */
@@ -374,7 +398,11 @@ static void pflash_write(PFlashCFI02 *pfl, hwaddr offset,
                     break;
                 }
             }
-            pfl->status = 0x00 | ~(value & 0x80);
+            /*
+             * While programming, status bit DQ7 should hold the opposite
+             * value from how it was programmed.
+             */
+            set_dq7(pfl, ~value);
             /* Let's pretend write is immediate */
             if (pfl->bypass)
                 goto do_bypass;
@@ -422,7 +450,7 @@ static void pflash_write(PFlashCFI02 *pfl, hwaddr offset,
                 memset(pfl->storage, 0xFF, pfl->chip_len);
                 pflash_update(pfl, 0, pfl->chip_len);
             }
-            pfl->status = 0x00;
+            set_dq7(pfl, 0x00);
             /* Let's wait 5 seconds before chip erase is done */
             timer_mod(&pfl->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
                       (NANOSECONDS_PER_SECOND * 5));
@@ -437,7 +465,7 @@ static void pflash_write(PFlashCFI02 *pfl, hwaddr offset,
                 memset(p + offset, 0xFF, pfl->sector_len);
                 pflash_update(pfl, offset, pfl->sector_len);
             }
-            pfl->status = 0x00;
+            set_dq7(pfl, 0x00);
             /* Let's wait 1/2 second before sector erase is done */
             timer_mod(&pfl->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
                       (NANOSECONDS_PER_SECOND / 2));