From owner-freebsd-current@FreeBSD.ORG Sat Sep 12 16:53:55 2009 Return-Path: Delivered-To: freebsd-current@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id C92AC1065696 for ; Sat, 12 Sep 2009 16:53:55 +0000 (UTC) (envelope-from nox@jelal.kn-bremen.de) Received: from smtp.kn-bremen.de (gelbbaer.kn-bremen.de [78.46.108.116]) by mx1.freebsd.org (Postfix) with ESMTP id 5917B8FC16 for ; Sat, 12 Sep 2009 16:53:55 +0000 (UTC) Received: by smtp.kn-bremen.de (Postfix, from userid 10) id 5D51C1E0029B; Sat, 12 Sep 2009 18:53:54 +0200 (CEST) Received: from triton8.kn-bremen.de (noident@localhost [127.0.0.1]) by triton8.kn-bremen.de (8.14.3/8.14.3) with ESMTP id n8CGqO49038209; Sat, 12 Sep 2009 18:52:24 +0200 (CEST) (envelope-from nox@triton8.kn-bremen.de) Received: (from nox@localhost) by triton8.kn-bremen.de (8.14.3/8.14.3/Submit) id n8CGqNpg038208; Sat, 12 Sep 2009 18:52:23 +0200 (CEST) (envelope-from nox) From: Juergen Lock Date: Sat, 12 Sep 2009 18:52:22 +0200 To: Jan Kiszka Message-ID: <20090912165222.GA38048@triton8.kn-bremen.de> References: <20090911213508.GA97446@triton8.kn-bremen.de> <4AAB938B.9080004@web.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AAB938B.9080004@web.de> User-Agent: Mutt/1.5.20 (2009-06-14) Cc: Olivier =?iso-8859-1?Q?Cochard-Labb=E9?= , freebsd-current@FreeBSD.org, Juergen Lock , qemu-devel@nongnu.org Subject: Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 12 Sep 2009 16:53:56 -0000 On Sat, Sep 12, 2009 at 02:26:51PM +0200, Jan Kiszka wrote: > Juergen Lock wrote: > > Hi! > > > > I got a report of FreeBSD guest's new uart(4) driver misbehaving in > > qemu again(?) (output stopping for no apparent reason), and now found > > out the problem is tx irqs (UART_IIR_THRI) are getting lost because > > serial_update_irq() checks for the rx condtion, > > ... if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR)) > > first before checking for the tx irq condition, > > ... if ((s->ier & UART_IER_THRI) && s->thr_ipending) > > which at least in this case (FreeBSD 8 guest after doing > > set console="comconsole" > > at the loader prompt or when simply echo'ing text to /dev/ttyu0 > > or typing to the serial port from cu(1) on a `regular' vga console) > > causes the second condition (.. && s->thr_ipending) to be never > > reached anymore, or only after a very long delay. Moving that > > condition up so it is checked first like this, > > > > Index: qemu/hw/serial.c > > @@ -189,7 +188,9 @@ static void serial_update_irq(SerialStat > > { > > uint8_t tmp_iir = UART_IIR_NO_INT; > > > > - if ((s->ier & UART_IER_RLSI) && (s->lsr & UART_LSR_INT_ANY)) { > > + if ((s->ier & UART_IER_THRI) && s->thr_ipending) { > > + tmp_iir = UART_IIR_THRI; > > + } else if ((s->ier & UART_IER_RLSI) && (s->lsr & UART_LSR_INT_ANY)) { > > tmp_iir = UART_IIR_RLSI; > > } else if ((s->ier & UART_IER_RDI) && s->timeout_ipending) { > > /* Note that(s->ier & UART_IER_RDI) can mask this interrupt, > > @@ -202,8 +203,6 @@ static void serial_update_irq(SerialStat > > } else if (s->recv_fifo.count >= s->recv_fifo.itl) { > > tmp_iir = UART_IIR_RDI; > > } > > - } else if ((s->ier & UART_IER_THRI) && s->thr_ipending) { > > - tmp_iir = UART_IIR_THRI; > > } else if ((s->ier & UART_IER_MSI) && (s->msr & UART_MSR_ANY_DELTA)) { > > tmp_iir = UART_IIR_MSI; > > } > > > > ...fixes the issue for me, but I'm not 100% sure if this might cause > > rx irqs to come (too?) late when a guest keeps sending while its > > receiving at the same time. Anyone care to comment? :) > > The reordering violates the 16550A spec in that RX event overrules TX in > the IRQ status register. Maybe something else is wrong but it's not the > ordering in serial_update_irq. Well one problem seems to be the rx condition, ... if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR)) is not enough to trigger an irq, yet still causes the following conditions not to be checked anymore at all. And ideed, fixing that seems to get my FreeBSD 8 guest back to working order as well: Index: qemu/hw/serial.c @@ -196,12 +195,10 @@ static void serial_update_irq(SerialStat * this is not in the specification but is observed on existing * hardware. */ tmp_iir = UART_IIR_CTI; - } else if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR)) { - if (!(s->fcr & UART_FCR_FE)) { - tmp_iir = UART_IIR_RDI; - } else if (s->recv_fifo.count >= s->recv_fifo.itl) { - tmp_iir = UART_IIR_RDI; - } + } else if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR) && + (!(s->fcr & UART_FCR_FE) || + s->recv_fifo.count >= s->recv_fifo.itl)) { + tmp_iir = UART_IIR_RDI; } else if ((s->ier & UART_IER_THRI) && s->thr_ipending) { tmp_iir = UART_IIR_THRI; } else if ((s->ier & UART_IER_MSI) && (s->msr & UART_MSR_ANY_DELTA)) { Signed-off-by: Juergen Lock