[PATCH v3] hw/char/pl011: Enable TxFIFO and async transmission

[Gavin Shan <gshan@redhat.com>]

The depth of TxFIFO can be 1 or 16 depending on LCR[4]. The TxFIFO is
disabled when its depth is 1. It's nice to have TxFIFO enabled if
possible because more characters can be piled and transmitted at once,
which would have less overhead. Besides, we can be blocked because of
qemu_chr_fe_write_all(), which isn't nice.

This enables TxFIFO if possible. On ther other hand, the asynchronous
transmission is enabled if needed, as we did in hw/char/cadence_uart.c

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
v3: Use PL011() to do data type conversion
    Return G_SOURCE_REMOVE when the backend is disconnected in pl011_xmit()
    Drop parenthesis in the condition validating @size in pl011_write_fifo()
---
 hw/char/pl011.c         | 105 +++++++++++++++++++++++++++++++++++++---
 include/hw/char/pl011.h |   3 ++
 2 files changed, 102 insertions(+), 6 deletions(-)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 13e784f9d9..dccb8c42b0 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -169,6 +169,73 @@ static void pl011_set_read_trigger(PL011State *s)
         s->read_trigger = 1;
 }
 
+static gboolean pl011_xmit(GIOChannel *chan, GIOCondition cond, void *opaque)
+{
+    PL011State *s = PL011(opaque);
+    int ret;
+
+    /* Drain FIFO if there is no backend */
+    if (!qemu_chr_fe_backend_connected(&s->chr)) {
+        s->write_count = 0;
+        s->flags &= ~PL011_FLAG_TXFF;
+        s->flags |= PL011_FLAG_TXFE;
+        return G_SOURCE_REMOVE;
+    }
+
+    /* Nothing to do */
+    if (!s->write_count) {
+        return FALSE;
+    }
+
+    ret = qemu_chr_fe_write(&s->chr, s->write_fifo, s->write_count);
+    if (ret > 0) {
+        s->write_count -= ret;
+        memmove(s->write_fifo, s->write_fifo + ret, s->write_count);
+        s->flags &= ~PL011_FLAG_TXFF;
+        if (!s->write_count) {
+            s->flags |= PL011_FLAG_TXFE;
+        }
+    }
+
+    if (s->write_count) {
+        s->watch_tag = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
+                                             pl011_xmit, s);
+        if (!s->watch_tag) {
+            s->write_count = 0;
+            s->flags &= ~PL011_FLAG_TXFF;
+            s->flags |= PL011_FLAG_TXFE;
+            return FALSE;
+        }
+    }
+
+    s->int_level |= PL011_INT_TX;
+    pl011_update(s);
+    return FALSE;
+}
+
+static void pl011_write_fifo(void *opaque, const unsigned char *buf, int size)
+{
+    PL011State *s = PL011(opaque);
+    int depth = (s->lcr & 0x10) ? 16 : 1;
+
+    if (size >= depth - s->write_count) {
+        size = depth - s->write_count;
+    }
+
+    if (size > 0) {
+        memcpy(s->write_fifo + s->write_count, buf, size);
+        s->write_count += size;
+        if (s->write_count >= depth) {
+            s->flags |= PL011_FLAG_TXFF;
+        }
+        s->flags &= ~PL011_FLAG_TXFE;
+    }
+
+    if (!s->watch_tag) {
+        pl011_xmit(NULL, G_IO_OUT, s);
+    }
+}
+
 static void pl011_write(void *opaque, hwaddr offset,
                         uint64_t value, unsigned size)
 {
@@ -179,13 +246,8 @@ static void pl011_write(void *opaque, hwaddr offset,
 
     switch (offset >> 2) {
     case 0: /* UARTDR */
-        /* ??? Check if transmitter is enabled.  */
         ch = value;
-        /* XXX this blocks entire thread. Rewrite to use
-         * qemu_chr_fe_write and background I/O callbacks */
-        qemu_chr_fe_write_all(&s->chr, &ch, 1);
-        s->int_level |= PL011_INT_TX;
-        pl011_update(s);
+        pl011_write_fifo(opaque, &ch, 1);
         break;
     case 1: /* UARTRSR/UARTECR */
         s->rsr = 0;
@@ -207,7 +269,16 @@ static void pl011_write(void *opaque, hwaddr offset,
         if ((s->lcr ^ value) & 0x10) {
             s->read_count = 0;
             s->read_pos = 0;
+
+            if (s->watch_tag) {
+                g_source_remove(s->watch_tag);
+                s->watch_tag = 0;
+            }
+            s->write_count = 0;
+            s->flags &= ~PL011_FLAG_TXFF;
+            s->flags |= PL011_FLAG_TXFE;
         }
+
         s->lcr = value;
         pl011_set_read_trigger(s);
         break;
@@ -292,6 +363,24 @@ static const MemoryRegionOps pl011_ops = {
     .endianness = DEVICE_NATIVE_ENDIAN,
 };
 
+static bool pl011_write_fifo_needed(void *opaque)
+{
+    PL011State *s = PL011(opaque);
+    return s->write_count > 0;
+}
+
+static const VMStateDescription vmstate_pl011_write_fifo = {
+    .name = "pl011/write_fifo",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = pl011_write_fifo_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_INT32(write_count, PL011State),
+        VMSTATE_UINT8_ARRAY(write_fifo, PL011State, 16),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 static const VMStateDescription vmstate_pl011 = {
     .name = "pl011",
     .version_id = 2,
@@ -314,6 +403,10 @@ static const VMStateDescription vmstate_pl011 = {
         VMSTATE_INT32(read_count, PL011State),
         VMSTATE_INT32(read_trigger, PL011State),
         VMSTATE_END_OF_LIST()
+    },
+    .subsections = (const VMStateDescription * []) {
+        &vmstate_pl011_write_fifo,
+        NULL
     }
 };
 
diff --git a/include/hw/char/pl011.h b/include/hw/char/pl011.h
index 14187165c6..9d1c24db48 100644
--- a/include/hw/char/pl011.h
+++ b/include/hw/char/pl011.h
@@ -38,6 +38,7 @@ typedef struct PL011State {
     uint32_t int_enabled;
     uint32_t int_level;
     uint32_t read_fifo[16];
+    uint8_t  write_fifo[16];
     uint32_t ilpr;
     uint32_t ibrd;
     uint32_t fbrd;
@@ -45,6 +46,8 @@ typedef struct PL011State {
     int read_pos;
     int read_count;
     int read_trigger;
+    int write_count;
+    guint watch_tag;
     CharBackend chr;
     qemu_irq irq[6];
     const unsigned char *id;
-- 
2.23.0