Re: [Qemu-devel] [RFC PATCH v2 4/6] hw/pci: introduce bridge-only vendor-specific capability to provide some hints to firmware

[Michael S. Tsirkin]

On Sun, Jul 23, 2017 at 01:15:41AM +0300, Aleksandr Bezzubikov wrote:
> On PCI init PCI bridges may need some
> extra info about bus number to reserve, IO, memory and
> prefetchable memory limits. QEMU can provide this
> with special

with a special

> vendor-specific PCI capability.
> 
> Sizes of limits match ones from
> PCI Type 1 Configuration Space Header,
> number of buses to reserve occupies only 1 byte 
> since it is the size of Subordinate Bus Number register.
> 
> Signed-off-by: Aleksandr Bezzubikov <address@hidden>
> ---
>  hw/pci/pci_bridge.c         | 27 +++++++++++++++++++++++++++
>  include/hw/pci/pci_bridge.h | 18 ++++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/hw/pci/pci_bridge.c b/hw/pci/pci_bridge.c
> index 720119b..8ec6c2c 100644
> --- a/hw/pci/pci_bridge.c
> +++ b/hw/pci/pci_bridge.c
> @@ -408,6 +408,33 @@ void pci_bridge_map_irq(PCIBridge *br, const char* 
> bus_name,
>      br->bus_name = bus_name;
>  }
>  
> +
> +int pci_bridge_help_cap_init(PCIDevice *dev, int cap_offset,

help? should be qemu_cap_init?

> +                              uint8_t bus_reserve, uint32_t io_limit,
> +                              uint16_t mem_limit, uint64_t pref_limit,
> +                              Error **errp)
> +{
> +    size_t cap_len = sizeof(PCIBridgeQemuCap);
> +    PCIBridgeQemuCap cap;

This leaks info to guest. You want to init all fields here:

cap = {
 .len = ....
};

> +
> +    cap.len = cap_len;
> +    cap.bus_res = bus_reserve;
> +    cap.io_lim = io_limit & 0xFF;
> +    cap.io_lim_upper = io_limit >> 8 & 0xFFFF;
> +    cap.mem_lim = mem_limit;
> +    cap.pref_lim = pref_limit & 0xFFFF;
> +    cap.pref_lim_upper = pref_limit >> 16 & 0xFFFFFFFF;

Please use pci_set_word etc or cpu_to_leXX.

I think it's easiest to replace struct with a set of macros then
pci_set_word does the work for you.


> +
> +    int offset = pci_add_capability(dev, PCI_CAP_ID_VNDR,
> +                                    cap_offset, cap_len, errp);
> +    if (offset < 0) {
> +        return offset;
> +    }
> +
> +    memcpy(dev->config + offset + 2, (char *)&cap + 2, cap_len - 2);

+2 is yacky. See how virtio does it:

    memcpy(dev->config + offset + PCI_CAP_FLAGS, &cap->cap_len,
           cap->cap_len - PCI_CAP_FLAGS);


> +    return 0;
> +}
> +
>  static const TypeInfo pci_bridge_type_info = {
>      .name = TYPE_PCI_BRIDGE,
>      .parent = TYPE_PCI_DEVICE,
> diff --git a/include/hw/pci/pci_bridge.h b/include/hw/pci/pci_bridge.h
> index ff7cbaa..c9f642c 100644
> --- a/include/hw/pci/pci_bridge.h
> +++ b/include/hw/pci/pci_bridge.h
> @@ -67,4 +67,22 @@ void pci_bridge_map_irq(PCIBridge *br, const char* 
> bus_name,
>  #define  PCI_BRIDGE_CTL_DISCARD_STATUS       0x400   /* Discard timer status 
> */
>  #define  PCI_BRIDGE_CTL_DISCARD_SERR 0x800   /* Discard timer SERR# enable */
>  
> +typedef struct PCIBridgeQemuCap {
> +    uint8_t id;     /* Standard PCI capability header field */
> +    uint8_t next;   /* Standard PCI capability header field */
> +    uint8_t len;    /* Standard PCI vendor-specific capability header field 
> */
> +    uint8_t bus_res;
> +    uint32_t pref_lim_upper;

Big endian? Ugh.

> +    uint16_t pref_lim;
> +    uint16_t mem_lim;

I'd say we need 64 bit for memory.

> +    uint16_t io_lim_upper;
> +    uint8_t io_lim;
> +    uint8_t padding;

IMHO each type should have a special "don't care" flag
that would mean "I don't know".


> +} PCIBridgeQemuCap;

You don't really need this struct in the header. And pls document all fields.

> +
> +int pci_bridge_help_cap_init(PCIDevice *dev, int cap_offset,
> +                              uint8_t bus_reserve, uint32_t io_limit,
> +                              uint16_t mem_limit, uint64_t pref_limit,
> +                              Error **errp);
> +
>  #endif /* QEMU_PCI_BRIDGE_H */
> -- 
> 2.7.4