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    SubjectRe: [PATCH] SR-IOV: correct broken resource alignment calculations
    * Matthew Wilcox (matthew@wil.cx) wrote:
    > On Fri, Aug 28, 2009 at 12:17:14PM -0700, Chris Wright wrote:
    > > An SR-IOV capable device includes an SR-IOV PCIe capability which
    > > describes the Virtual Function (VF) BAR requirements. A typical SR-IOV
    > > device can support multiple VFs whose BARs must be in a contiguous region,
    > > effectively an array of VF BARs. The BAR reports the size requirement
    > > for a single VF. We calculate the full range needed by simply multiplying
    > > the VF BAR size with the number of possible VFs and create a resource
    > > spanning the full range.
    > >
    > > This all seems sane enough except it artificially inflates the alignment
    > > requirement for the VF BAR. The VF BAR need only be aligned to the size
    > > of a single BAR not the contiguous range of VF BARs. This can cause us
    > > to fail to allocate resources for the BAR despite the fact that we
    > > actually have enough space.
    > >
    > > This patch adds a support for a new resource alignment type,
    > > IORESOURCE_VSIZEALIGN, and allows struct resource to keep track of the
    > > size requirements of a VF BAR which are smaller than the full resource
    > > size. This could also be done all within the PCI layer w/out bloating
    > > struct resource or using the last available bit for alignment types.
    >
    > Yes, I think that would be preferable. We have a *LOT* of resources in
    > the kernel, and the embedded folks would not find it funny if they all
    > grew in size suddenly.

    OK, I'll send that momentarily. It has one downside which is we re-read
    the BAR size multiple times.


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