From patchwork Thu Jan 28 23:13:31 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Fix lost serial TX interrupts. Report receive overruns. X-Patchwork-Submitter: "Justin T. Gibbs" X-Patchwork-Id: 43888 Message-Id: <4B621A1B.6090309@FreeBSD.org> To: qemu-devel@nongnu.org Date: Thu, 28 Jan 2010 16:13:31 -0700 From: "Justin T. Gibbs" List-Id: qemu-devel.nongnu.org 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 } --- 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;