Re: [Qemu-devel] [PATCH] Fix lost serial TX interrupts. Report receive overruns.

[Anthony Liguori]

On 01/28/2010 05:13 PM, Justin T. Gibbs wrote:
> 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 <address@hidden>

This patch is malformed.  Please export the patch from a git tree via 
git-format-patch.

Regards,

Anthony Liguori

> --- serial.c.orig    Thu Jan 14 15:18:00 2010
> +++ serial.c    Thu Jan 28 15:36:04 2010
> @@ -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;
>      }