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    Driver core: add notification of bus events · 116af378
    Benjamin Herrenschmidt 提交于
    I finally did as you suggested and added the notifier to the struct
    bus_type itself. There are still problems to be expected is something
    attaches to a bus type where the code can hook in different struct
    device sub-classes (which is imho a big bogosity but I won't even try to
    argue that case now) but it will solve nicely a number of issues I've
    had so far.
    
    That also means that clients interested in registering for such
    notifications have to do it before devices are added and after bus types
    are registered. Fortunately, most bus types that matter for the various
    usage scenarios I have in mind are registerd at postcore_initcall time,
    which means I have a really nice spot at arch_initcall time to add my
    notifiers.
    
    There are 4 notifications provided. Device being added (before hooked to
    the bus) and removed (failure of previous case or after being unhooked
    from the bus), along with driver being bound to a device and about to be
    unbound.
    
    The usage I have for these are:
    
     - The 2 first ones are used to maintain a struct device_ext that is
    hooked to struct device.firmware_data. This structure contains for now a
    pointer to the Open Firmware node related to the device (if any), the
    NUMA node ID (for quick access to it) and the DMA operations pointers &
    iommu table instance for DMA to/from this device. For bus types I own
    (like IBM VIO or EBUS), I just maintain that structure directly from the
    bus code when creating the devices. But for bus types managed by generic
    code like PCI or platform (actually, of_platform which is a variation of
    platform linked to Open Firmware device-tree), I need this notifier.
    
     - The other two ones have a completely different usage scenario. I have
    cases where multiple devices and their drivers depend on each other. For
    example, the IBM EMAC network driver needs to attach to a MAL DMA engine
    which is a separate device, and a PHY interface which is also a separate
    device. They are all of_platform_device's (well, about to be with my
    upcoming patches) but there is no say in what precise order the core
    will "probe" them and instanciate the various modules. The solution I
    found for that is to have the drivers for emac to use multithread_probe,
    and wait for a driver to be bound to the target MAL and PHY control
    devices (the device-tree contains reference to the MAL and PHY interface
    nodes, which I can then match to of_platform_devices). Right now, I've
    been polling, but with that notifier, I can more cleanly wait (with a
    timeout of course).
    Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
    Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
    116af378
dd.c 9.6 KB