Re: [Qemu-devel] [PATCH RFC v2 2/2] hw/pci: handle unassigned pci addresses

[Marcel Apfelbaum <marcel.a@redhat.com>]

On Mon, 2013-09-09 at 14:40 +0300, Michael S. Tsirkin wrote:
> On Mon, Sep 09, 2013 at 02:11:54PM +0300, Marcel Apfelbaum wrote:
> > Created a MemoryRegion with negative priority that
> > spans over all the pci address space.
> > It "intercepts" the accesses to unassigned pci
> > address space and will follow the pci spec:
> >  1. returns -1 on read
> >  2. does nothing on write
> >  3. sets the RECEIVED MASTER ABORT bit in the STATUS register
> >     of the device that initiated the transaction
> > 
> > Note: This implementation assumes that all the reads/writes to
> > the pci address space are done by the cpu.
> > 
> > Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
> > ---
> > Changes from v1:
> >  - "pci-unassigned-mem" MemoryRegion resides now in PCIBus and not on
> >     various Host Bridges
> >  - "pci-unassgined-mem" does not have a ".valid.accept" field and
> >     implements read write methods
> > 
> >  hw/pci/pci.c             | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> >  include/hw/pci/pci_bus.h |  1 +
> >  2 files changed, 47 insertions(+)
> > 
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index d00682e..b6a8026 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -283,6 +283,43 @@ const char *pci_root_bus_path(PCIDevice *dev)
> >      return rootbus->qbus.name;
> >  }
> >  
> > +static void unassigned_mem_access(PCIBus *bus)
> > +{
> > +    /* FIXME assumption: memory access to the pci address
> > +     * space is always initiated by the host bridge
> 
> /* Always
>  * like
>  * this
>  */
> 
> /* Not
>  * like this */
OK

> 
> > +     * (device 0 on the bus) */
> 
> Can't we pass the master device in?
> We are still left with the assumption that
> there's a single master, but at least
> we get rid of the assumption that it's
> always device 0 function 0.
> 
> 
> > +    PCIDevice *d = bus->devices[0];
> > +    if (!d) {
> > +        return;
> > +    }
> > +
> > +    pci_word_test_and_set_mask(d->config + PCI_STATUS,
> > +                               PCI_STATUS_REC_MASTER_ABORT);
> 
> Probably should check and set secondary status for
> a bridge device.
I wanted to add the support for bridges later,
I am struggling with some issues with PCI bridges.
 
> 
> > +}
> > +
> > +static uint64_t unassigned_mem_read(void *opaque, hwaddr addr, unsigned size)
> > +{
> > +    PCIBus *bus = opaque;
> > +    unassigned_mem_access(bus);
> > +
> > +    return -1ULL;
> > +}
> > +
> > +static void unassigned_mem_write(void *opaque, hwaddr addr, uint64_t val,
> > +                                unsigned size)
> > +{
> > +    PCIBus *bus = opaque;
> > +    unassigned_mem_access(bus);
> > +}
> > +
> > +static const MemoryRegionOps unassigned_mem_ops = {
> > +    .read = unassigned_mem_read,
> > +    .write = unassigned_mem_write,
> > +    .endianness = DEVICE_NATIVE_ENDIAN,
> > +};
> > +
> > +#define UNASSIGNED_MEM_PRIORITY -1
> > +
> >  static void pci_bus_init(PCIBus *bus, DeviceState *parent,
> >                           const char *name,
> >                           MemoryRegion *address_space_mem,
> 
> 
> I would rename "unassigned" to "pci_master_Abort_" everywhere.
Are you sure about the capital "A"?

For the memory ops I suppose is OK, but the MemoryRegion name
I think it should remain "unassigned_mem"; it will be strange
to name it pci_master_Abort_mem.
> 
> Call things by what they do not how they are used.
> 
> > @@ -294,6 +331,15 @@ static void pci_bus_init(PCIBus *bus, DeviceState *parent,
> >      bus->address_space_mem = address_space_mem;
> >      bus->address_space_io = address_space_io;
> >  
> > +
> > +    memory_region_init_io(&bus->unassigned_mem, OBJECT(bus),
> > +                          &unassigned_mem_ops, bus, "pci-unassigned",
> > +                          memory_region_size(bus->address_space_mem));
> > +    memory_region_add_subregion_overlap(bus->address_space_mem,
> > +                                        bus->address_space_mem->addr,
> > +                                        &bus->unassigned_mem,
> > +                                        UNASSIGNED_MEM_PRIORITY);
> > +
> >      /* host bridge */
> >      QLIST_INIT(&bus->child);
> >
> 
> It seems safer to add an API for enabling this functionality.
> Something like
> 
> pci_set_master_for_master_abort(PCIBus *, PCIDevice *);
I started to implement that way, but it would be strange (I think) 
to see in the code the above method because almost all the pci devices
can be master devices.

I selected an "implicit" implementation so for this reason exactly.
We do not really select a master, but a "master for writes/reads on
pci address space". Selecting device 0 on the bus automatically for
this makes more sense to me.
What do you think?
Marcel 

> 
>   
> > diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
> > index 9df1788..4cc25a3 100644
> > --- a/include/hw/pci/pci_bus.h
> > +++ b/include/hw/pci/pci_bus.h
> > @@ -23,6 +23,7 @@ struct PCIBus {
> >      PCIDevice *parent_dev;
> >      MemoryRegion *address_space_mem;
> >      MemoryRegion *address_space_io;
> > +    MemoryRegion unassigned_mem;
> >  
> >      QLIST_HEAD(, PCIBus) child; /* this will be replaced by qdev later */
> >      QLIST_ENTRY(PCIBus) sibling;/* this will be replaced by qdev later */
> > -- 
> > 1.8.3.1
>