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    SubjectRe: how to get virtual address from dma address


    On 6 Oct 2001, Jes Sorensen wrote:

    > >>>>> "Paul" == Paul Mackerras <paulus@samba.org> writes:
    >
    > Paul> David S. Miller writes:
    > >> I can not even count on one hand how many people I've helped
    > >> converting, who wanted a bus_to_virt() and when I showed them how
    > >> to do it with information the device provided already they said "oh
    > >> wow, I never would have thought of that". That process won't
    > >> happen as often with the suggested feature.
    >
    > Paul> Well, let's see if we can come up with a way to achieve this
    > Paul> goal as well as the other.
    >
    > Paul> I look at all the hash-table stuff in the usb-ohci driver and I
    > Paul> think to myself about all the complexity that is there (and I
    > Paul> haven't managed to convince myself yet that it is actually
    > Paul> SMP-safe) and all the time wasted doing that stuff, when on
    > Paul> probably 95% of the machines that use the usb-ohci driver, the
    > Paul> hashing stuff is totally unnecessary. I am talking about
    > Paul> powermacs, which don't have an iommu, and where the reverse
    > Paul> mapping is as simple as adding a constant.
    >
    > I haven't looked at the ohci driver at all, however doesn't it return
    > anything but the dma address? No index, no offset, no nothing? If
    > thats the case, someone really needs to go visit the designers with a
    > large bat ;-(

    I would apply the bat to people that wants such a dma to virtual general
    translation. This thing is obviously gross shit.

    I would also apply the bat to people that look into stuff of other people
    and, instead of trying to actually understand the code, just give a look
    and send inappropriate statements to the list.

    Gérard.

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