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    SubjectRe: Exposing ROM's though sysfs
    On Tuesday, August 3, 2004 6:57 pm, Benjamin Herrenschmidt wrote:
    > Jesse did a pretty good summary of what features need to be provided
    > though. Note also that this "arbitration" layer may also need an in-kernel
    > API for things like vgacon or whatever may want to "grab" access to the
    > VGA device.

    Good point, I forgot about that. Theoretically, as long as a device has been
    POSTed, vgacon should work just fine with some small tweaks on platforms that
    allow mapping of the VGA framebuffer.

    > I suggest that at this point, we don't try to bother with simultaneous
    > access to devices on separate PCI domains, but just use an in-kernel
    > semaphore to arbitrate the single user at a given point in time who "owns"
    > the VGA access, whatever bus it is on. So we need 2 things, both in-kernel
    > and for userland:

    Sounds good. Cards usually POST pretty quickly, so that won't be a problem
    until someone puts 32 cards in a system (oh wait, that's not too far off :).

    > - A way to identify a VGA device on a given bus. Could this be a PCI
    > ID (or in kernel a pci_dev ?). That would mean no support for non-PCI
    > stuffs, how bad would that be ?

    I personally don't care about anything but PCI, AGP and PCI-Express, but you
    make a good point about embedded stuff.

    > - Userland should use read/write for IOs imho, either to a /dev device
    > (with maybe an ioctl to switch between PIO and VGA mem, though mmap is
    > better for the later) or to some sysfs entry (in which case, can we add
    > mmap call to a sysfs attribute ? last time I looked, it wasn't simple).

    Yeah, that sounds reasonable. I'd vote for a real device as opposed to sysfs
    files, for now at least.

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