Patchwork [4/4] pci: interrupt disable bit support

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Submitter Michael S. Tsirkin
Date Nov. 25, 2009, 4:59 p.m.
Message ID <20091125165906.GE24783@redhat.com>
Download mbox | patch
Permalink /patch/39350/
State New
Headers show

Comments

Michael S. Tsirkin - Nov. 25, 2009, 4:59 p.m.
interrupt disable bit is mandatory in PCI spec,
so we must implement it to be spec compliant.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/pci.c |   57 ++++++++++++++++++++++++++++++++++++++++-----------------
 hw/pci.h |    4 ++++
 2 files changed, 44 insertions(+), 17 deletions(-)
Isaku Yamahata - Nov. 26, 2009, 3:04 a.m.
On Wed, Nov 25, 2009 at 06:59:06PM +0200, Michael S. Tsirkin wrote:
> interrupt disable bit is mandatory in PCI spec,
> so we must implement it to be spec compliant.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/pci.c |   57 ++++++++++++++++++++++++++++++++++++++++-----------------
>  hw/pci.h |    4 ++++
>  2 files changed, 44 insertions(+), 17 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 844664b..3daae46 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -114,12 +114,43 @@ static void pci_update_irq_status(PCIDevice *dev)
>      }
>  }
>  
> +static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> +{
> +    PCIBus *bus;
> +    for (;;) {
> +        bus = pci_dev->bus;
> +        irq_num = bus->map_irq(pci_dev, irq_num);
> +        if (bus->set_irq)
> +            break;
> +        pci_dev = bus->parent_dev;
> +    }
> +    bus->irq_count[irq_num] += change;
> +    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);

Let's use ! instead of != 0 for consistency.


> +}
> +
> +/* Update irq disabled field after config space change,
> + * assert/deassert interrupts if necessary. */
> +static void pci_update_irq_disabled(PCIDevice *d)
> +{
> +    int i;
> +    int disabled = !!(pci_get_word(d->config + PCI_COMMAND) &
> +                      PCI_COMMAND_INTX_DISABLE);
> +    if (disabled == d->irq_disabled)
> +        return;
> +    d->irq_disabled = disabled;
> +    for (i = 0; i < ARRAY_SIZE(d->irq_state); ++i) {
> +        int state = d->irq_state[i];
> +        pci_change_irq_level(d, i, disabled ? -state : state);
> +    }
> +}
> +

"if (!changed) return" check is in pci_set_irq().
So if d->irq_state[i] == 0, bus->set_irq() will be called again.
I suppose this isn't your intention.
I suppose !changed check should be in pci_change_irq_level() instead of pci_set_irq().


>  static void pci_device_reset(PCIDevice *dev)
>  {
>      int r;
>  
>      memset(dev->irq_state, 0, sizeof dev->irq_state);
>      dev->irq_status = 0;
> +    dev->irq_disabled = 0;
>      pci_update_irq_status(dev);
>      dev->config[PCI_COMMAND] &= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY |
>                                    PCI_COMMAND_MASTER);
> @@ -345,6 +376,7 @@ int pci_device_load(PCIDevice *s, QEMUFile *f)
>      }
>      /* Restore the interrupt status bit. */
>      pci_update_irq_status(s);
> +    pci_update_irq_disabled(s);
>      return ret;
>  }
>  
> @@ -458,7 +490,8 @@ static void pci_init_wmask(PCIDevice *dev)
>      dev->wmask[PCI_CACHE_LINE_SIZE] = 0xff;
>      dev->wmask[PCI_INTERRUPT_LINE] = 0xff;
>      pci_set_word(dev->wmask + PCI_COMMAND,
> -                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER);
> +                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER |
> +                 PCI_COMMAND_INTX_DISABLE);
>  
>      memset(dev->wmask + PCI_CONFIG_HEADER_SIZE, 0xff,
>             config_size - PCI_CONFIG_HEADER_SIZE);
> @@ -903,26 +936,14 @@ void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val, int l)
>          ranges_overlap(addr, l, PCI_ROM_ADDRESS1, 4) ||
>          range_covers_byte(addr, l, PCI_COMMAND))
>          pci_update_mappings(d);
> +
> +    if (range_covers_byte(addr, l, PCI_COMMAND))
> +        pci_update_irq_disabled(d);
>  }
>  
>  /***********************************************************/
>  /* generic PCI irq support */
>  
> -static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> -{
> -    PCIBus *bus;
> -    for (;;) {
> -        bus = pci_dev->bus;
> -        irq_num = bus->map_irq(pci_dev, irq_num);
> -        if (bus->set_irq)
> -            break;
> -        pci_dev = bus->parent_dev;
> -    }
> -    bus->irq_count[irq_num] += change;
> -    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
> -}
> -
> -
>  /* 0 <= irq_num <= 3. level must be 0 or 1 */
>  static void pci_set_irq(void *opaque, int irq_num, int level)
>  {
> @@ -935,7 +956,9 @@ static void pci_set_irq(void *opaque, int irq_num, int level)
>  
>      pci_dev->irq_state[irq_num] = level;
>      pci_dev->irq_status += change;
> -    pci_update_irq_status(s);
> +    pci_update_irq_status(pci_dev);
> +    if (pci_dev->irq_disabled)
> +        return;
>      pci_change_irq_level(pci_dev, irq_num, change);
>  }
>  
> diff --git a/hw/pci.h b/hw/pci.h
> index c3f2c3f..994b8bc 100644
> --- a/hw/pci.h
> +++ b/hw/pci.h
> @@ -101,6 +101,7 @@ typedef struct PCIIORegion {
>  #define  PCI_COMMAND_IO		0x1	/* Enable response in I/O space */
>  #define  PCI_COMMAND_MEMORY	0x2	/* Enable response in Memory space */
>  #define  PCI_COMMAND_MASTER	0x4	/* Enable bus master */
> +#define  PCI_COMMAND_INTX_DISABLE 0x400 /* INTx Emulation Disable */
>  #define PCI_STATUS              0x06    /* 16 bits */
>  #define  PCI_STATUS_INTERRUPT   0x08
>  #define PCI_REVISION_ID         0x08    /* 8 bits  */
> @@ -226,6 +227,9 @@ struct PCIDevice {
>      /* Sum of all irq levels. Used to implement irq status register. */
>      int irq_status;
>  
> +    /* Whether interrupts are disabled by command bit. */
> +    int irq_disabled;
> +
>      /* Capability bits */
>      uint32_t cap_present;
>
Michael S. Tsirkin - Nov. 26, 2009, 9:53 a.m.
On Thu, Nov 26, 2009 at 12:04:51PM +0900, Isaku Yamahata wrote:
> On Wed, Nov 25, 2009 at 06:59:06PM +0200, Michael S. Tsirkin wrote:
> > interrupt disable bit is mandatory in PCI spec,
> > so we must implement it to be spec compliant.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  hw/pci.c |   57 ++++++++++++++++++++++++++++++++++++++++-----------------
> >  hw/pci.h |    4 ++++
> >  2 files changed, 44 insertions(+), 17 deletions(-)
> > 
> > diff --git a/hw/pci.c b/hw/pci.c
> > index 844664b..3daae46 100644
> > --- a/hw/pci.c
> > +++ b/hw/pci.c
> > @@ -114,12 +114,43 @@ static void pci_update_irq_status(PCIDevice *dev)
> >      }
> >  }
> >  
> > +static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> > +{
> > +    PCIBus *bus;
> > +    for (;;) {
> > +        bus = pci_dev->bus;
> > +        irq_num = bus->map_irq(pci_dev, irq_num);
> > +        if (bus->set_irq)
> > +            break;
> > +        pci_dev = bus->parent_dev;
> > +    }
> > +    bus->irq_count[irq_num] += change;
> > +    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
> 
> Let's use ! instead of != 0 for consistency.
> 

This patch simply moves code, so it's better to keep it
the same - this way git blame can find it.
A separate patch to clean this might be a good idea.

> > +}
> > +
> > +/* Update irq disabled field after config space change,
> > + * assert/deassert interrupts if necessary. */
> > +static void pci_update_irq_disabled(PCIDevice *d)
> > +{
> > +    int i;
> > +    int disabled = !!(pci_get_word(d->config + PCI_COMMAND) &
> > +                      PCI_COMMAND_INTX_DISABLE);
> > +    if (disabled == d->irq_disabled)
> > +        return;
> > +    d->irq_disabled = disabled;
> > +    for (i = 0; i < ARRAY_SIZE(d->irq_state); ++i) {
> > +        int state = d->irq_state[i];
> > +        pci_change_irq_level(d, i, disabled ? -state : state);
> > +    }
> > +}
> > +
> 
> "if (!changed) return" check is in pci_set_irq().
> So if d->irq_state[i] == 0, bus->set_irq() will be called again.
> I suppose this isn't your intention.

Good catch, thanks!

> I suppose !changed check should be in pci_change_irq_level() instead of pci_set_irq().
> 

The fix is different: in fact pci_update_irq_disabled
should never call pci_change_irq_level with change value 0.
that -state should have been 1 - state.
I'll fix this. Thanks!

> >  static void pci_device_reset(PCIDevice *dev)
> >  {
> >      int r;
> >  
> >      memset(dev->irq_state, 0, sizeof dev->irq_state);
> >      dev->irq_status = 0;
> > +    dev->irq_disabled = 0;
> >      pci_update_irq_status(dev);
> >      dev->config[PCI_COMMAND] &= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY |
> >                                    PCI_COMMAND_MASTER);
> > @@ -345,6 +376,7 @@ int pci_device_load(PCIDevice *s, QEMUFile *f)
> >      }
> >      /* Restore the interrupt status bit. */
> >      pci_update_irq_status(s);
> > +    pci_update_irq_disabled(s);
> >      return ret;
> >  }
> >  
> > @@ -458,7 +490,8 @@ static void pci_init_wmask(PCIDevice *dev)
> >      dev->wmask[PCI_CACHE_LINE_SIZE] = 0xff;
> >      dev->wmask[PCI_INTERRUPT_LINE] = 0xff;
> >      pci_set_word(dev->wmask + PCI_COMMAND,
> > -                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER);
> > +                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER |
> > +                 PCI_COMMAND_INTX_DISABLE);
> >  
> >      memset(dev->wmask + PCI_CONFIG_HEADER_SIZE, 0xff,
> >             config_size - PCI_CONFIG_HEADER_SIZE);
> > @@ -903,26 +936,14 @@ void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val, int l)
> >          ranges_overlap(addr, l, PCI_ROM_ADDRESS1, 4) ||
> >          range_covers_byte(addr, l, PCI_COMMAND))
> >          pci_update_mappings(d);
> > +
> > +    if (range_covers_byte(addr, l, PCI_COMMAND))
> > +        pci_update_irq_disabled(d);
> >  }
> >  
> >  /***********************************************************/
> >  /* generic PCI irq support */
> >  
> > -static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> > -{
> > -    PCIBus *bus;
> > -    for (;;) {
> > -        bus = pci_dev->bus;
> > -        irq_num = bus->map_irq(pci_dev, irq_num);
> > -        if (bus->set_irq)
> > -            break;
> > -        pci_dev = bus->parent_dev;
> > -    }
> > -    bus->irq_count[irq_num] += change;
> > -    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
> > -}
> > -
> > -
> >  /* 0 <= irq_num <= 3. level must be 0 or 1 */
> >  static void pci_set_irq(void *opaque, int irq_num, int level)
> >  {
> > @@ -935,7 +956,9 @@ static void pci_set_irq(void *opaque, int irq_num, int level)
> >  
> >      pci_dev->irq_state[irq_num] = level;
> >      pci_dev->irq_status += change;
> > -    pci_update_irq_status(s);
> > +    pci_update_irq_status(pci_dev);
> > +    if (pci_dev->irq_disabled)
> > +        return;
> >      pci_change_irq_level(pci_dev, irq_num, change);
> >  }
> >  
> > diff --git a/hw/pci.h b/hw/pci.h
> > index c3f2c3f..994b8bc 100644
> > --- a/hw/pci.h
> > +++ b/hw/pci.h
> > @@ -101,6 +101,7 @@ typedef struct PCIIORegion {
> >  #define  PCI_COMMAND_IO		0x1	/* Enable response in I/O space */
> >  #define  PCI_COMMAND_MEMORY	0x2	/* Enable response in Memory space */
> >  #define  PCI_COMMAND_MASTER	0x4	/* Enable bus master */
> > +#define  PCI_COMMAND_INTX_DISABLE 0x400 /* INTx Emulation Disable */
> >  #define PCI_STATUS              0x06    /* 16 bits */
> >  #define  PCI_STATUS_INTERRUPT   0x08
> >  #define PCI_REVISION_ID         0x08    /* 8 bits  */
> > @@ -226,6 +227,9 @@ struct PCIDevice {
> >      /* Sum of all irq levels. Used to implement irq status register. */
> >      int irq_status;
> >  
> > +    /* Whether interrupts are disabled by command bit. */
> > +    int irq_disabled;
> > +
> >      /* Capability bits */
> >      uint32_t cap_present;
> >  
> 
> -- 
> yamahata
Michael S. Tsirkin - Nov. 26, 2009, 12:38 p.m.
On Thu, Nov 26, 2009 at 11:53:16AM +0200, Michael S. Tsirkin wrote:
> On Thu, Nov 26, 2009 at 12:04:51PM +0900, Isaku Yamahata wrote:
> > On Wed, Nov 25, 2009 at 06:59:06PM +0200, Michael S. Tsirkin wrote:
> > > interrupt disable bit is mandatory in PCI spec,
> > > so we must implement it to be spec compliant.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > >  hw/pci.c |   57 ++++++++++++++++++++++++++++++++++++++++-----------------
> > >  hw/pci.h |    4 ++++
> > >  2 files changed, 44 insertions(+), 17 deletions(-)
> > > 
> > > diff --git a/hw/pci.c b/hw/pci.c
> > > index 844664b..3daae46 100644
> > > --- a/hw/pci.c
> > > +++ b/hw/pci.c
> > > @@ -114,12 +114,43 @@ static void pci_update_irq_status(PCIDevice *dev)
> > >      }
> > >  }
> > >  
> > > +static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> > > +{
> > > +    PCIBus *bus;
> > > +    for (;;) {
> > > +        bus = pci_dev->bus;
> > > +        irq_num = bus->map_irq(pci_dev, irq_num);
> > > +        if (bus->set_irq)
> > > +            break;
> > > +        pci_dev = bus->parent_dev;
> > > +    }
> > > +    bus->irq_count[irq_num] += change;
> > > +    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
> > 
> > Let's use ! instead of != 0 for consistency.
> > 
> 
> This patch simply moves code, so it's better to keep it
> the same - this way git blame can find it.
> A separate patch to clean this might be a good idea.
> 
> > > +}
> > > +
> > > +/* Update irq disabled field after config space change,
> > > + * assert/deassert interrupts if necessary. */
> > > +static void pci_update_irq_disabled(PCIDevice *d)
> > > +{
> > > +    int i;
> > > +    int disabled = !!(pci_get_word(d->config + PCI_COMMAND) &
> > > +                      PCI_COMMAND_INTX_DISABLE);
> > > +    if (disabled == d->irq_disabled)
> > > +        return;
> > > +    d->irq_disabled = disabled;
> > > +    for (i = 0; i < ARRAY_SIZE(d->irq_state); ++i) {
> > > +        int state = d->irq_state[i];
> > > +        pci_change_irq_level(d, i, disabled ? -state : state);
> > > +    }
> > > +}
> > > +
> > 
> > "if (!changed) return" check is in pci_set_irq().
> > So if d->irq_state[i] == 0, bus->set_irq() will be called again.
> > I suppose this isn't your intention.
> 
> Good catch, thanks!

Thinking about this more, in fact, it is harmless to call set_irq
with the same level as th old one, and this
is not on datapath.
So yes, this is the intention.

> > I suppose !changed check should be in pci_change_irq_level() instead of pci_set_irq().
> > 
> 
> The fix is different: in fact pci_update_irq_disabled
> should never call pci_change_irq_level with change value 0.
> that -state should have been 1 - state.
> I'll fix this. Thanks!

In fact, you were right.
While calling pci_change_irq_level with change 0 is harmless,
it's cleaner to move the check within that function.
I'll do that.

> > >  static void pci_device_reset(PCIDevice *dev)
> > >  {
> > >      int r;
> > >  
> > >      memset(dev->irq_state, 0, sizeof dev->irq_state);
> > >      dev->irq_status = 0;
> > > +    dev->irq_disabled = 0;
> > >      pci_update_irq_status(dev);
> > >      dev->config[PCI_COMMAND] &= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY |
> > >                                    PCI_COMMAND_MASTER);
> > > @@ -345,6 +376,7 @@ int pci_device_load(PCIDevice *s, QEMUFile *f)
> > >      }
> > >      /* Restore the interrupt status bit. */
> > >      pci_update_irq_status(s);
> > > +    pci_update_irq_disabled(s);
> > >      return ret;
> > >  }
> > >  
> > > @@ -458,7 +490,8 @@ static void pci_init_wmask(PCIDevice *dev)
> > >      dev->wmask[PCI_CACHE_LINE_SIZE] = 0xff;
> > >      dev->wmask[PCI_INTERRUPT_LINE] = 0xff;
> > >      pci_set_word(dev->wmask + PCI_COMMAND,
> > > -                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER);
> > > +                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER |
> > > +                 PCI_COMMAND_INTX_DISABLE);
> > >  
> > >      memset(dev->wmask + PCI_CONFIG_HEADER_SIZE, 0xff,
> > >             config_size - PCI_CONFIG_HEADER_SIZE);
> > > @@ -903,26 +936,14 @@ void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val, int l)
> > >          ranges_overlap(addr, l, PCI_ROM_ADDRESS1, 4) ||
> > >          range_covers_byte(addr, l, PCI_COMMAND))
> > >          pci_update_mappings(d);
> > > +
> > > +    if (range_covers_byte(addr, l, PCI_COMMAND))
> > > +        pci_update_irq_disabled(d);
> > >  }
> > >  
> > >  /***********************************************************/
> > >  /* generic PCI irq support */
> > >  
> > > -static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> > > -{
> > > -    PCIBus *bus;
> > > -    for (;;) {
> > > -        bus = pci_dev->bus;
> > > -        irq_num = bus->map_irq(pci_dev, irq_num);
> > > -        if (bus->set_irq)
> > > -            break;
> > > -        pci_dev = bus->parent_dev;
> > > -    }
> > > -    bus->irq_count[irq_num] += change;
> > > -    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
> > > -}
> > > -
> > > -
> > >  /* 0 <= irq_num <= 3. level must be 0 or 1 */
> > >  static void pci_set_irq(void *opaque, int irq_num, int level)
> > >  {
> > > @@ -935,7 +956,9 @@ static void pci_set_irq(void *opaque, int irq_num, int level)
> > >  
> > >      pci_dev->irq_state[irq_num] = level;
> > >      pci_dev->irq_status += change;
> > > -    pci_update_irq_status(s);
> > > +    pci_update_irq_status(pci_dev);
> > > +    if (pci_dev->irq_disabled)
> > > +        return;
> > >      pci_change_irq_level(pci_dev, irq_num, change);
> > >  }
> > >  
> > > diff --git a/hw/pci.h b/hw/pci.h
> > > index c3f2c3f..994b8bc 100644
> > > --- a/hw/pci.h
> > > +++ b/hw/pci.h
> > > @@ -101,6 +101,7 @@ typedef struct PCIIORegion {
> > >  #define  PCI_COMMAND_IO		0x1	/* Enable response in I/O space */
> > >  #define  PCI_COMMAND_MEMORY	0x2	/* Enable response in Memory space */
> > >  #define  PCI_COMMAND_MASTER	0x4	/* Enable bus master */
> > > +#define  PCI_COMMAND_INTX_DISABLE 0x400 /* INTx Emulation Disable */
> > >  #define PCI_STATUS              0x06    /* 16 bits */
> > >  #define  PCI_STATUS_INTERRUPT   0x08
> > >  #define PCI_REVISION_ID         0x08    /* 8 bits  */
> > > @@ -226,6 +227,9 @@ struct PCIDevice {
> > >      /* Sum of all irq levels. Used to implement irq status register. */
> > >      int irq_status;
> > >  
> > > +    /* Whether interrupts are disabled by command bit. */
> > > +    int irq_disabled;
> > > +
> > >      /* Capability bits */
> > >      uint32_t cap_present;
> > >  
> > 
> > -- 
> > yamahata
Michael S. Tsirkin - Nov. 26, 2009, 1:21 p.m.
On Thu, Nov 26, 2009 at 12:04:51PM +0900, Isaku Yamahata wrote:
> On Wed, Nov 25, 2009 at 06:59:06PM +0200, Michael S. Tsirkin wrote:
> > interrupt disable bit is mandatory in PCI spec,
> > so we must implement it to be spec compliant.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  hw/pci.c |   57 ++++++++++++++++++++++++++++++++++++++++-----------------
> >  hw/pci.h |    4 ++++
> >  2 files changed, 44 insertions(+), 17 deletions(-)
> > 
> > diff --git a/hw/pci.c b/hw/pci.c
> > index 844664b..3daae46 100644
> > --- a/hw/pci.c
> > +++ b/hw/pci.c
> > @@ -114,12 +114,43 @@ static void pci_update_irq_status(PCIDevice *dev)
> >      }
> >  }
> >  
> > +static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> > +{
> > +    PCIBus *bus;
> > +    for (;;) {
> > +        bus = pci_dev->bus;
> > +        irq_num = bus->map_irq(pci_dev, irq_num);
> > +        if (bus->set_irq)
> > +            break;
> > +        pci_dev = bus->parent_dev;
> > +    }
> > +    bus->irq_count[irq_num] += change;
> > +    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
> 
> Let's use ! instead of != 0 for consistency.

By the way, this would have to be !!, not !.
So not sure there's much consistency to be gained:
!= appears in pci.c more times than !!.

Patch

diff --git a/hw/pci.c b/hw/pci.c
index 844664b..3daae46 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -114,12 +114,43 @@  static void pci_update_irq_status(PCIDevice *dev)
     }
 }
 
+static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
+{
+    PCIBus *bus;
+    for (;;) {
+        bus = pci_dev->bus;
+        irq_num = bus->map_irq(pci_dev, irq_num);
+        if (bus->set_irq)
+            break;
+        pci_dev = bus->parent_dev;
+    }
+    bus->irq_count[irq_num] += change;
+    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
+}
+
+/* Update irq disabled field after config space change,
+ * assert/deassert interrupts if necessary. */
+static void pci_update_irq_disabled(PCIDevice *d)
+{
+    int i;
+    int disabled = !!(pci_get_word(d->config + PCI_COMMAND) &
+                      PCI_COMMAND_INTX_DISABLE);
+    if (disabled == d->irq_disabled)
+        return;
+    d->irq_disabled = disabled;
+    for (i = 0; i < ARRAY_SIZE(d->irq_state); ++i) {
+        int state = d->irq_state[i];
+        pci_change_irq_level(d, i, disabled ? -state : state);
+    }
+}
+
 static void pci_device_reset(PCIDevice *dev)
 {
     int r;
 
     memset(dev->irq_state, 0, sizeof dev->irq_state);
     dev->irq_status = 0;
+    dev->irq_disabled = 0;
     pci_update_irq_status(dev);
     dev->config[PCI_COMMAND] &= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY |
                                   PCI_COMMAND_MASTER);
@@ -345,6 +376,7 @@  int pci_device_load(PCIDevice *s, QEMUFile *f)
     }
     /* Restore the interrupt status bit. */
     pci_update_irq_status(s);
+    pci_update_irq_disabled(s);
     return ret;
 }
 
@@ -458,7 +490,8 @@  static void pci_init_wmask(PCIDevice *dev)
     dev->wmask[PCI_CACHE_LINE_SIZE] = 0xff;
     dev->wmask[PCI_INTERRUPT_LINE] = 0xff;
     pci_set_word(dev->wmask + PCI_COMMAND,
-                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER);
+                 PCI_COMMAND_IO | PCI_COMMAND_MEMORY | PCI_COMMAND_MASTER |
+                 PCI_COMMAND_INTX_DISABLE);
 
     memset(dev->wmask + PCI_CONFIG_HEADER_SIZE, 0xff,
            config_size - PCI_CONFIG_HEADER_SIZE);
@@ -903,26 +936,14 @@  void pci_default_write_config(PCIDevice *d, uint32_t addr, uint32_t val, int l)
         ranges_overlap(addr, l, PCI_ROM_ADDRESS1, 4) ||
         range_covers_byte(addr, l, PCI_COMMAND))
         pci_update_mappings(d);
+
+    if (range_covers_byte(addr, l, PCI_COMMAND))
+        pci_update_irq_disabled(d);
 }
 
 /***********************************************************/
 /* generic PCI irq support */
 
-static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
-{
-    PCIBus *bus;
-    for (;;) {
-        bus = pci_dev->bus;
-        irq_num = bus->map_irq(pci_dev, irq_num);
-        if (bus->set_irq)
-            break;
-        pci_dev = bus->parent_dev;
-    }
-    bus->irq_count[irq_num] += change;
-    bus->set_irq(bus->irq_opaque, irq_num, bus->irq_count[irq_num] != 0);
-}
-
-
 /* 0 <= irq_num <= 3. level must be 0 or 1 */
 static void pci_set_irq(void *opaque, int irq_num, int level)
 {
@@ -935,7 +956,9 @@  static void pci_set_irq(void *opaque, int irq_num, int level)
 
     pci_dev->irq_state[irq_num] = level;
     pci_dev->irq_status += change;
-    pci_update_irq_status(s);
+    pci_update_irq_status(pci_dev);
+    if (pci_dev->irq_disabled)
+        return;
     pci_change_irq_level(pci_dev, irq_num, change);
 }
 
diff --git a/hw/pci.h b/hw/pci.h
index c3f2c3f..994b8bc 100644
--- a/hw/pci.h
+++ b/hw/pci.h
@@ -101,6 +101,7 @@  typedef struct PCIIORegion {
 #define  PCI_COMMAND_IO		0x1	/* Enable response in I/O space */
 #define  PCI_COMMAND_MEMORY	0x2	/* Enable response in Memory space */
 #define  PCI_COMMAND_MASTER	0x4	/* Enable bus master */
+#define  PCI_COMMAND_INTX_DISABLE 0x400 /* INTx Emulation Disable */
 #define PCI_STATUS              0x06    /* 16 bits */
 #define  PCI_STATUS_INTERRUPT   0x08
 #define PCI_REVISION_ID         0x08    /* 8 bits  */
@@ -226,6 +227,9 @@  struct PCIDevice {
     /* Sum of all irq levels. Used to implement irq status register. */
     int irq_status;
 
+    /* Whether interrupts are disabled by command bit. */
+    int irq_disabled;
+
     /* Capability bits */
     uint32_t cap_present;