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    SubjectRe: [PATCH 4/6] ehea: header files
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    On Mon, 2006-08-14 at 14:53 +0200, Jan-Bernd Themann wrote:
    > Michael Ellerman wrote:
    > >> --- linux-2.6.18-rc4-orig/drivers/net/ehea/ehea.h 1969-12-31 16:00:00.000000000 -0800
    > >> +++ kernel/drivers/net/ehea/ehea.h 2006-08-08 23:59:39.927452928 -0700
    > >> +
    > >> +#define EHEA_PAGESHIFT 12
    > >> +#define EHEA_PAGESIZE 4096UL
    > >> +#define EHEA_CACHE_LINE 128
    > >
    > > This looks like a very bad idea, what happens if you're running on a
    > > machine with 64K pages?
    > >
    >
    > The EHEA_PAGESIZE define is needed for queue management to hardware side.

    You mean the eHEA has its own concept of page size? Separate from the
    page size used by the MMU?

    > >> +/*
    > >> + * h_galpa:
    > >> + * for pSeries this is a 64bit memory address where
    > >> + * I/O memory is mapped into CPU address space
    > >> + */
    > >> +
    > >> +struct h_galpa {
    > >> + u64 fw_handle;
    > >> +};
    > >
    > > What is a h_galpa? And why does it need a struct if it's just a u64?
    > >
    >
    > The eHEA chip is not PCI attached but directly connected to a proprietary
    > bus. Currently, we can access it by a simple 64 bit address, but this is not
    > true in all cases. Having a struct here allows us to encapsulate the chip
    > register access and to respond to changes to system hardware.
    >
    > We'll change the name to h_epa meaning "ehea physical address"

    Hmm, I'm not convinced. Having the struct doesn't really encapsulate
    much, because most of the places where you use the h_galpa struct just
    pull out the fw_handle anyway. So if you change the layout of the struct
    you're going to have to change most of the code anyway. And in the
    meantime it makes the code a lot less readable, most people understand
    what "u64 addr" is about, whereas "struct h_galpa" is much less
    meaningful. </2c>

    cheers

    --
    Michael Ellerman
    IBM OzLabs

    wwweb: http://michael.ellerman.id.au
    phone: +61 2 6212 1183 (tie line 70 21183)

    We do not inherit the earth from our ancestors,
    we borrow it from our children. - S.M.A.R.T Person
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