Fix lost serial TX interrupts. Report receive overruns.

This patch compliments the patch submitted by Jergen Lock and further improves the performance of QEMU's serial emulation with FreeBSD's uart(9) driver.

o Implement receive overrun status. The FreeBSD uart driver relies on this status in it's probe routine to determine the size of the FIFO supported.
o As per the 16550 spec, do not overwrite the RX FIFO on an RX overrun.
o Do not allow TX or RX FIFO overruns to increment the data valid count beyond the size of the FIFO.
o For reads of the IIR register, only clear the "TX holding register emtpy interrupt" if the read reports this interrupt. This is required by the specification and avoids losing TX interrupts when other,
higher
priority interrupts (usually RX) are reported first.

Signed-off-by Justin T. Gibbs <[email protected]>

serial.c Thu Jan 28 15:36:04 2010 renamed from serial.c.orig Thu Jan 14 15:18:00 2010 +20 -8

@@ -169,11 +169,19 @@
 {
     SerialFIFO *f = (fifo) ? &s->recv_fifo : &s->xmit_fifo;
 
-    f->data[f->head++] = chr;
+    /* Receive overruns do not overwrite FIFO contents. */
+    if (fifo == XMIT_FIFO || f->count < UART_FIFO_LENGTH) {
 
-    if (f->head == UART_FIFO_LENGTH)
-        f->head = 0;
-    f->count++;
+        f->data[f->head++] = chr;
+
+        if (f->head == UART_FIFO_LENGTH)
+            f->head = 0;
+    }
+
+    if (f->count < UART_FIFO_LENGTH)
+        f->count++;
+    else if (fifo == RECV_FIFO)
+        s->lsr |= UART_LSR_OE;
 
     return 1;
 }

@@ -533,8 +541,10 @@
         break;
     case 2:
         ret = s->iir;
+        if (ret & UART_IIR_THRI) {
             s->thr_ipending = 0;
-        serial_update_irq(s);
+            serial_update_irq(s);
+        }
         break;
     case 3:
         ret = s->lcr;

@@ -544,9 +554,9 @@
         break;
     case 5:
         ret = s->lsr;
-        /* Clear break interrupt */
-        if (s->lsr & UART_LSR_BI) {
-            s->lsr &= ~UART_LSR_BI;
+        /* Clear break and overrun interrupts */
+        if (s->lsr & (UART_LSR_BI|UART_LSR_OE)) {
+            s->lsr &= ~(UART_LSR_BI|UART_LSR_OE);
             serial_update_irq(s);
         }
         break;

@@ -629,6 +639,8 @@
         /* call the timeout receive callback in 4 char transmit time */
         qemu_mod_timer(s->fifo_timeout_timer, qemu_get_clock 
 (vm_clock) + s->char_transmit_time * 4);
     } else {
+        if (s->lsr & UART_LSR_DR)
+            s->lsr |= UART_LSR_OE;
         s->rbr = buf[0];
         s->lsr |= UART_LSR_DR;

     }

From 7a941b3fcd298b60bb14744b8fae422d86298197 Mon Sep 17 00:00:00 2001

Properly formatted patch now attached.

--
Justin