[Qemu-devel] Re: [PATCH 16/23] pci: pcie host and mmcfg support.

[Michael S. Tsirkin]

On Tue, Oct 06, 2009 at 07:02:59PM +0900, Isaku Yamahata wrote:
> On Mon, Oct 05, 2009 at 01:41:21PM +0200, Michael S. Tsirkin wrote:
> > On Mon, Oct 05, 2009 at 07:06:56PM +0900, Isaku Yamahata wrote:
> > > @@ -1052,9 +1242,10 @@ PCIDevice *pci_create_simple(PCIBus *bus, int 
> > > devfn, const char *name)
> > >  
> > >  static int pci_find_space(PCIDevice *pdev, uint8_t size)
> > >  {
> > > +    int config_size = pcie_config_size(pdev);
> > >      int offset = PCI_CONFIG_HEADER_SIZE;
> > >      int i;
> > > -    for (i = PCI_CONFIG_HEADER_SIZE; i < PCI_CONFIG_SPACE_SIZE; ++i)
> > > +    for (i = PCI_CONFIG_HEADER_SIZE; i < config_size; ++i)
> > >          if (pdev->used[i])
> > >              offset = i + 1;
> > >          else if (i - offset + 1 == size)
> > > diff --git a/hw/pci.h b/hw/pci.h
> > > index 00f2b78..1f402d2 100644
> > > --- a/hw/pci.h
> > > +++ b/hw/pci.h
> > > @@ -175,20 +175,26 @@ enum {
> > >      QEMU_PCI_CAP_MSIX = 0x1,
> > >  };
> > >  
> > > +/* Size of the standart PCIe config space: 4KB */
> > > +#define PCIE_CONFIG_SPACE_SIZE  0x1000
> > > +#define PCIE_EXT_CONFIG_SPACE_SIZE                      \
> > > +    (PCIE_CONFIG_SPACE_SIZE - PCI_CONFIG_SPACE_SIZE)
> > > +
> > >  struct PCIDevice {
> > >      DeviceState qdev;
> > > +
> > >      /* PCI config space */
> > > -    uint8_t config[PCI_CONFIG_SPACE_SIZE];
> > > +    uint8_t *config;
> > >  
> > >      /* Used to enable config checks on load. Note that writeable bits are
> > >       * never checked even if set in cmask. */
> > > -    uint8_t cmask[PCI_CONFIG_SPACE_SIZE];
> > > +    uint8_t *cmask;
> > >  
> > >      /* Used to implement R/W bytes */
> > > -    uint8_t wmask[PCI_CONFIG_SPACE_SIZE];
> > > +    uint8_t *wmask;
> > >  
> > >      /* Used to allocate config space for capabilities. */
> > > -    uint8_t used[PCI_CONFIG_SPACE_SIZE];
> > > +    uint8_t *used;
> > >  
> > >      /* the following fields are read only */
> > >      PCIBus *bus;
> > 
> > 
> > So I thought about this some more, and I think that this change
> > in unnecessary. PCI Express adds support for extended 4K
> > configuration space, but the only thing that must reside
> > there is the optional advanced error reporting capability,
> > which I don't think we'll need to implement, ever.
> >
> > Everything else can reside in the first 256 bytes, just as for regular
> > PCI. And pci code already returns 0 for accesses outside the first 256
> > bytes, so express specific code is necessary.
> 
> I agree with you for emulated PCI express device
> (which doesn't exist for now). However I oppose it for other reason.
> 
> My purpose is to direct attach PCIe device to a guest including
> AER emulation somehow.

For now, if I were you, I would just ignore AER.

> When direct attaching PCIe native device to a guest,
> we don't have any control on how its configuration space is used.
> When an error is reported on host via AER, I'd like to pass 
> the error to guest in some manner. So I want AER too in a sense.

Since what you will want to do is forward stuff to a physical device,
you likely won't need to keep anything in memory at all.
So express code might just do
        if (offset > 256)
                write_to_physical_device();
But, let's take these things one at a time.
For one, device assignment is not upstream at all.

By the way, a general question: how was this tested?  Did you manage to
make guest generate mmconfig transactions?  Which guests do this?

> -- 
> yamahata