[Qemu-devel] Re: >2 serial ports?

[Gerd Hoffmann <kraxel@redhat.com>]

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On 03/17/10 09:38, Michael Tokarev wrote:
> Since 0.12, it appears that kvm does not allow more than
> 2 serial ports for a guest:
>
> $ kvm \
>   -serial unix:s1,server,nowait \
>   -serial unix:s2,server,nowait \
>   -serial unix:s3,server,nowait
> isa irq 4 already assigned
>
> Is there a work-around for this?

Oh, well, yes, I remember.  qemu is more strict on ISA irq sharing now. 
  A bit too strict.

/me goes dig out a old patch which never made it upstream for some 
reason I forgot.  Attached.

HTH,
   Gerd

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>From 7d5d53e8a23544ac6413487a8ecdd43537ade9f3 Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Fri, 11 Sep 2009 13:43:46 +0200
Subject: [PATCH] isa: refine irq reservations

There are a few cases where IRQ sharing on the ISA bus is used and
possible.  In general only devices of the same kind can do that.
A few use cases:

  * serial lines 1+3 share irq 4
  * serial lines 2+4 share irq 3
  * parallel ports share irq 7
  * ppc/prep: ide ports share irq 13

This patch refines the irq reservation mechanism for the isa bus to
handle those cases.  It keeps track of the driver which owns the IRQ in
question and allows irq sharing for devices handled by the same driver.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/isa-bus.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/hw/isa-bus.c b/hw/isa-bus.c
index 4d489d2..bd2f69c 100644
--- a/hw/isa-bus.c
+++ b/hw/isa-bus.c
@@ -26,6 +26,7 @@ struct ISABus {
     BusState qbus;
     qemu_irq *irqs;
     uint32_t assigned;
+    DeviceInfo *irq_owner[16];
 };
 static ISABus *isabus;
 
@@ -71,7 +72,9 @@ qemu_irq isa_reserve_irq(int isairq)
         exit(1);
     }
     if (isabus->assigned & (1 << isairq)) {
-        fprintf(stderr, "isa irq %d already assigned\n", isairq);
+        DeviceInfo *owner = isabus->irq_owner[isairq];
+        fprintf(stderr, "isa irq %d already assigned (%s)\n",
+                isairq, owner ? owner->name : "unknown");
         exit(1);
     }
     isabus->assigned |= (1 << isairq);
@@ -82,10 +85,17 @@ void isa_init_irq(ISADevice *dev, qemu_irq *p, int isairq)
 {
     assert(dev->nirqs < ARRAY_SIZE(dev->isairq));
     if (isabus->assigned & (1 << isairq)) {
-        fprintf(stderr, "isa irq %d already assigned\n", isairq);
-        exit(1);
+        DeviceInfo *owner = isabus->irq_owner[isairq];
+        if (owner == dev->qdev.info) {
+            /* irq sharing is ok in case the same driver handles both */;
+        } else {
+            fprintf(stderr, "isa irq %d already assigned (%s)\n",
+                    isairq, owner ? owner->name : "unknown");
+            exit(1);
+        }
     }
     isabus->assigned |= (1 << isairq);
+    isabus->irq_owner[isairq] = dev->qdev.info;
     dev->isairq[dev->nirqs] = isairq;
     *p = isabus->irqs[isairq];
     dev->nirqs++;
-- 
1.6.6.1