Re: [Qemu-devel] Using PCI config space to indicate config location

[Rusty Russell]

Gerd Hoffmann <address@hidden> writes:
> So how about this:
>
> (1) Add a vendor specific pci capability for new-style virtio.
>     Specifies the pci bar used for new-style virtio registers.
>     Guests can use it to figure whenever new-style virtio is
>     supported and to map the correct bar (which will probably
>     be bar 1 in most cases).

This was closer to the original proposal[1], which I really liked (you
can layout bars however you want).  Anthony thought that vendor
capabilities were a PCI-e feature, but it seems they're blessed in PCI
2.3.

So let's return to that proposal, giving something like this:

/* IDs for different capabilities.  Must all exist. */
/* FIXME: Do we win from separating ISR, NOTIFY and COMMON? */
/* Common configuration */
#define VIRTIO_PCI_CAP_COMMON_CFG       1
/* Notifications */
#define VIRTIO_PCI_CAP_NOTIFY_CFG       2
/* ISR access */
#define VIRTIO_PCI_CAP_ISR_CFG          3
/* Device specific confiuration */
#define VIRTIO_PCI_CAP_DEVICE_CFG       4

/* This is the PCI capability header: */
struct virtio_pci_cap {
        u8 cap_vndr;    /* Generic PCI field: PCI_CAP_ID_VNDR */
        u8 cap_next;    /* Generic PCI field: next ptr. */
        u8 cap_len;     /* Generic PCI field: sizeof(struct virtio_pci_cap). */
        u8 cfg_type;    /* One of the VIRTIO_PCI_CAP_*_CFG. */
        u8 bar;         /* Where to find it. */
        u8 unused;
        __le16 offset;  /* Offset within bar. */
        __le32 length;  /* Length. */
};

This means qemu can point the isr_cfg into the legacy area if it wants.
In fact, it can put everything in BAR0 if it wants.

Thoughts?
Rusty.