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[Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver) |
Date: |
Sat, 12 Sep 2009 19:00:57 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
Juergen Lock wrote:
> 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 <address@hidden>
Yep, that does make sense!
Acked-by: Jan Kiszka <address@hidden>
But I also but Stefano on CC as he introduced the logic above.
Jan
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- [Qemu-devel] qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Juergen Lock, 2009/09/11
- [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Jan Kiszka, 2009/09/12
- [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Juergen Lock, 2009/09/12
- [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver),
Jan Kiszka <=
- Re: [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Stefano Stabellini, 2009/09/14
- Re: [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Aurelien Jarno, 2009/09/16
- Re: [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Juergen Lock, 2009/09/23
- Re: [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Aurelien Jarno, 2009/09/24
- Re: [Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Juergen Lock, 2009/09/24
[Qemu-devel] Re: qemu serial: lost tx irqs (affectig FreeBSD's new uart(4) driver), Olivier Cochard-Labbé, 2009/09/12