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    SubjectRe: [RFC PATCH 1/2] pci: don't assume pref memio are 64bit -v3
    On Thu, Apr 23, 2009 at 08:13:04AM -0700, Yinghai Lu wrote:
    > at least the one in mm/memory_hotplug.c
    > /* add this memory to iomem resource */
    > static struct resource *register_memory_resource(u64 start, u64 size)
    > {
    > struct resource *res;
    > res = kzalloc(sizeof(struct resource), GFP_KERNEL);
    > BUG_ON(!res);
    > res->name = "System RAM";
    > res->start = start;
    > res->end = start + size - 1;
    > if (request_resource(&iomem_resource, res) < 0) {
    > printk("System RAM resource %llx - %llx cannot be added\n",
    > (unsigned long long)res->start, (unsigned long long)res->end);
    > kfree(res);
    > res = NULL;
    > }
    > return res;
    > }

    Indeed. It's a really strong argument against mem64 resource approach.

    On the other hand, it shows that getting 64-bit allocations right is
    indeed a very complex issue - without well defined root bus ranges
    there is a high risk of unexpectedly breaking something, like that memory
    hotplug. Oh well...

    So if the main purpose is to prevent 32-bit allocations in the DAC
    area, some mix of your v2 and v3 patches seems to be the way to go.
    That is

    - keep IORESOURCE_MEM_64 bits from -v3, but drop iomem32_resource
    and iomem64_resource things;

    - pass "max" argument to allocate_resource() like you did in -v2,
    but *only* then allocating from iomem_resource (r == &iomem_resource).
    Also, instead of max = 0xffffffff use something like max = PCIBIOS_MAX_MEM_32.

    #ifndef PCIBIOS_MAX_MEM_32
    #define PCIBIOS_MAX_MEM_32 (-1)

    This should preserve the current behaviour of pci_bus_alloc_resource()
    on non-x86 arches; overridden in arch/x86/include/asm/pci.h:
    #define PCIBIOS_MAX_MEM_32 0xffffffff

    > check bits 0-3 and check PCI_PREF_BASE_UPPER32 register being r/w ?

    Yes. If these bits are zero, no further checks are needed -
    bridge is 32-bit. If they aren't, do additional check for
    PCI_PREF_BASE_UPPER32 being non-zero or writable, but *only*
    if this prefetch resource is not already allocated (res->parent == NULL),
    just for safety reasons - we don't want to disconnect the allocated
    range from the bus even for a short time.


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