ps2: use the whole ps2 buffer but keep queue size

Extend the used ps2 buffer size to the available buffer size but
keep the maximum ps2 queue size.

The next patch needs a few bytes of the larger buffer size.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20210810133258.8231-1-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/input/ps2.c

@@ -74,7 +74,12 @@
 #define MOUSE_STATUS_ENABLED    0x20
 #define MOUSE_STATUS_SCALE21    0x10
 
-#define PS2_QUEUE_SIZE 16  /* Buffer size required by PS/2 protocol */
+/*
+ * PS/2 buffer size. Keep 256 bytes for compatibility with
+ * older QEMU versions.
+ */
+#define PS2_BUFFER_SIZE     256
+#define PS2_QUEUE_SIZE      16  /* Queue size required by PS/2 protocol */
 
 /* Bits for 'modifiers' field in PS2KbdState */
 #define MOD_CTRL_L  (1 << 0)
@@ -85,9 +90,7 @@
 #define MOD_ALT_R   (1 << 5)
 
 typedef struct {
-    /* Keep the data array 256 bytes long, which compatibility
-     with older qemu versions. */
-    uint8_t data[256];
+    uint8_t data[PS2_BUFFER_SIZE];
     int rptr, wptr, count;
 } PS2Queue;
 
@@ -200,8 +203,9 @@ void ps2_queue_noirq(PS2State *s, int b)
     }
 
     q->data[q->wptr] = b;
-    if (++q->wptr == PS2_QUEUE_SIZE)
+    if (++q->wptr == PS2_BUFFER_SIZE) {
         q->wptr = 0;
+    }
     q->count++;
 }
 
@@ -509,13 +513,15 @@ uint32_t ps2_read_data(PS2State *s)
            (needed for EMM386) */
         /* XXX: need a timer to do things correctly */
         index = q->rptr - 1;
-        if (index < 0)
-            index = PS2_QUEUE_SIZE - 1;
+        if (index < 0) {
+            index = PS2_BUFFER_SIZE - 1;
+        }
         val = q->data[index];
     } else {
         val = q->data[q->rptr];
-        if (++q->rptr == PS2_QUEUE_SIZE)
+        if (++q->rptr == PS2_BUFFER_SIZE) {
             q->rptr = 0;
+        }
         q->count--;
         /* reading deasserts IRQ */
         s->update_irq(s->update_arg, 0);
@@ -926,30 +932,17 @@ static void ps2_common_reset(PS2State *s)
 static void ps2_common_post_load(PS2State *s)
 {
     PS2Queue *q = &s->queue;
-    uint8_t i, size;
-    uint8_t tmp_data[PS2_QUEUE_SIZE];
 
-    /* set the useful data buffer queue size, < PS2_QUEUE_SIZE */
-    size = q->count;
+    /* set the useful data buffer queue size <= PS2_QUEUE_SIZE */
     if (q->count < 0) {
-        size = 0;
+        q->count = 0;
     } else if (q->count > PS2_QUEUE_SIZE) {
-        size = PS2_QUEUE_SIZE;
-    }
-
-    /* move the queue elements to the start of data array */
-    for (i = 0; i < size; i++) {
-        if (q->rptr < 0 || q->rptr >= sizeof(q->data)) {
-            q->rptr = 0;
-        }
-        tmp_data[i] = q->data[q->rptr++];
+        q->count = PS2_QUEUE_SIZE;
     }
-    memcpy(q->data, tmp_data, size);
 
-    /* reset rptr/wptr/count */
-    q->rptr = 0;
-    q->wptr = (size == PS2_QUEUE_SIZE) ? 0 : size;
-    q->count = size;
+    /* sanitize rptr and recalculate wptr */
+    q->rptr = q->rptr & (PS2_BUFFER_SIZE - 1);
+    q->wptr = (q->rptr + q->count) & (PS2_BUFFER_SIZE - 1);
 }
 
 static void ps2_kbd_reset(void *opaque)
@@ -1053,22 +1046,11 @@ static int ps2_kbd_post_load(void* opaque, int version_id)
     return 0;
 }
 
-static int ps2_kbd_pre_save(void *opaque)
-{
-    PS2KbdState *s = (PS2KbdState *)opaque;
-    PS2State *ps2 = &s->common;
-
-    ps2_common_post_load(ps2);
-
-    return 0;
-}
-
 static const VMStateDescription vmstate_ps2_keyboard = {
     .name = "ps2kbd",
     .version_id = 3,
     .minimum_version_id = 2,
     .post_load = ps2_kbd_post_load,
-    .pre_save = ps2_kbd_pre_save,
     .fields = (VMStateField[]) {
         VMSTATE_STRUCT(common, PS2KbdState, 0, vmstate_ps2_common, PS2State),
         VMSTATE_INT32(scan_enabled, PS2KbdState),
@@ -1093,22 +1075,11 @@ static int ps2_mouse_post_load(void *opaque, int version_id)
     return 0;
 }
 
-static int ps2_mouse_pre_save(void *opaque)
-{
-    PS2MouseState *s = (PS2MouseState *)opaque;
-    PS2State *ps2 = &s->common;
-
-    ps2_common_post_load(ps2);
-
-    return 0;
-}
-
 static const VMStateDescription vmstate_ps2_mouse = {
     .name = "ps2mouse",
     .version_id = 2,
     .minimum_version_id = 2,
     .post_load = ps2_mouse_post_load,
-    .pre_save = ps2_mouse_pre_save,
     .fields = (VMStateField[]) {
         VMSTATE_STRUCT(common, PS2MouseState, 0, vmstate_ps2_common, PS2State),
         VMSTATE_UINT8(mouse_status, PS2MouseState),