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From 1db8ec7f2caf255b94d1516e521768f553e01972 Mon Sep 17 00:00:00 2001
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From: Hans de Goede <hdegoede@redhat.com>
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Date: Fri, 5 Apr 2013 12:05:49 +0200
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Subject: [PATCH] ehci_free_packet: Discard finished packets when the queue is
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halted
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With pipelining it is possible to encounter a finished packet when cleaning
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the queue due to a halt. This happens when a non stall error happens while
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talking to a real device. In this case the queue on the usb-host side will
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continue processing packets, and we can have completed packets waiting in
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the queue after an error condition packet causing a halt.
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There are 2 reasons to discard the completed packets at this point, rather
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then writing them back to the guest:
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1) The guest expect to be able to cancel and/or change packets after the
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packet with the error without doing an unlink, so writing them back may
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confuse the guest.
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2) Since the queue does not advance when halted, the writing back of these
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packets will trigger an assert because p->qtdaddr != q->qtdaddr, causing qemu
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to abort.
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Note that discarding these packets means that the guest driver and the device
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will get out of sync! This is unfortunate, but should not be a problem since
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with a non stall error (iow an io-error) the 2 are out of sync already anyways.
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Still this patch adds a warning printf to signal this happening.
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Note that sofar this has only been seen with a DVB-T receiver, which gives
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of a MPEG-2 stream, which allows for recovering from lost packets, see:
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https://bugzilla.redhat.com/show_bug.cgi?id=890320
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Signed-off-by: Hans de Goede <hdegoede@redhat.com>
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---
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hw/usb/hcd-ehci.c | 18 +++++++++++-------
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1 file changed, 11 insertions(+), 7 deletions(-)
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diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
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index 6be11c5..6a787aa 100644
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--- a/hw/usb/hcd-ehci.c
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+++ b/hw/usb/hcd-ehci.c
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@@ -752,11 +752,10 @@ static EHCIPacket *ehci_alloc_packet(EHCIQueue *q)
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static void ehci_free_packet(EHCIPacket *p)
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{
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- if (p->async == EHCI_ASYNC_FINISHED) {
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+ if (p->async == EHCI_ASYNC_FINISHED &&
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+ !(p->queue->qh.token & QTD_TOKEN_HALT)) {
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EHCIQueue *q = p->queue;
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int state = ehci_get_state(q->ehci, q->async);
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- /* This is a normal, but rare condition (cancel racing completion) */
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- fprintf(stderr, "EHCI: Warning packet completed but not processed\n");
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ehci_state_executing(q);
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ehci_state_writeback(q);
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if (!(q->qh.token & QTD_TOKEN_HALT)) {
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@@ -767,12 +766,17 @@ static void ehci_free_packet(EHCIPacket *p)
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return;
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}
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trace_usb_ehci_packet_action(p->queue, p, "free");
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- if (p->async == EHCI_ASYNC_INITIALIZED) {
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- usb_packet_unmap(&p->packet, &p->sgl);
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- qemu_sglist_destroy(&p->sgl);
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- }
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if (p->async == EHCI_ASYNC_INFLIGHT) {
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usb_cancel_packet(&p->packet);
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+ }
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+ if (p->async == EHCI_ASYNC_FINISHED) {
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+ fprintf(stderr,
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+ "EHCI: Dropping completed packet from halted %s ep %02X\n",
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+ (p->pid == USB_TOKEN_IN) ? "in" : "out",
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+ get_field(p->queue->qh.epchar, QH_EPCHAR_EP));
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+
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+ }
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+ if (p->async != EHCI_ASYNC_NONE) {
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usb_packet_unmap(&p->packet, &p->sgl);
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qemu_sglist_destroy(&p->sgl);
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}
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