68 lines
2.8 KiB
Diff
68 lines
2.8 KiB
Diff
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From 90f23b109c482f23d04a943d1e41f79b33ce028a Mon Sep 17 00:00:00 2001
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From: Michael Tokarev <mjt@tls.msk.ru>
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Date: Wed, 19 Sep 2012 12:08:31 +0400
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Subject: [PATCH] Revert "serial: fix retry logic"
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This reverts commit 67c5322d7000fd105a926eec44bc1765b7d70bdd:
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I'm not sure if the retry logic has ever worked when not using FIFO mode. I
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found this while writing a test case although code inspection confirms it is
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definitely broken.
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The TSR retry logic will never actually happen because it is guarded by an
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'if (s->tsr_rety > 0)' but this is the only place that can ever make the
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variable greater than zero. That effectively makes the retry logic an 'if (0)
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I believe this is a typo and the intention was >= 0. Once this is fixed thoug
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I see double transmits with my test case. This is because in the non FIFO
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case, serial_xmit may get invoked while LSR.THRE is still high because the
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character was processed but the retransmit timer was still active.
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We can handle this by simply checking for LSR.THRE and returning early. It's
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possible that the FIFO paths also need some attention.
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Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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Even if the previous logic was never worked, new logic breaks stuff -
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namely,
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qemu -enable-kvm -nographic -kernel /boot/vmlinuz-$(uname -r) -append console=ttyS0 -serial pty
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the above command will cause the virtual machine to stuck at startup
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using 100% CPU till one connects to the pty and sends any char to it.
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Note this is rather typical invocation for various headless virtual
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machines by libvirt.
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So revert this change for now, till a better solution will be found.
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Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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---
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hw/serial.c | 4 +---
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1 file changed, 1 insertion(+), 3 deletions(-)
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diff --git a/hw/serial.c b/hw/serial.c
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index 056d823..c9fccf7 100644
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--- a/hw/serial.c
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+++ b/hw/serial.c
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@@ -327,8 +327,6 @@ static void serial_xmit(void *opaque)
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s->tsr = fifo_get(s,XMIT_FIFO);
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if (!s->xmit_fifo.count)
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s->lsr |= UART_LSR_THRE;
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- } else if ((s->lsr & UART_LSR_THRE)) {
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- return;
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} else {
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s->tsr = s->thr;
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s->lsr |= UART_LSR_THRE;
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@@ -340,7 +338,7 @@ static void serial_xmit(void *opaque)
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/* in loopback mode, say that we just received a char */
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serial_receive1(s, &s->tsr, 1);
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} else if (qemu_chr_fe_write(s->chr, &s->tsr, 1) != 1) {
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- if ((s->tsr_retry >= 0) && (s->tsr_retry <= MAX_XMIT_RETRY)) {
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+ if ((s->tsr_retry > 0) && (s->tsr_retry <= MAX_XMIT_RETRY)) {
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s->tsr_retry++;
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qemu_mod_timer(s->transmit_timer, new_xmit_ts + s->char_transmit_time);
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return;
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