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    SubjectRe: [PATCH 1/6] staging: vme: allow explicit assignment of bus numbers
    On Wed, Aug 10, 2011 at 01:50:17PM +0100, Martyn Welch wrote:
    > On 10/08/11 11:41, Manohar Vanga wrote:
    > > Hey Martyn,
    > >
    > >> I'm sorry, I'm still simply not convinced by this patch:
    > >>
    > >> 1) For a single bus driver (i.e. in the situation where we have 2 bridges of
    > >> the same type), the numbering of the buses is still dependent on the order
    > >> that they are found in the scan.
    > >
    > > Yes this is still a bug. But this patch doesn't address this case.
    > >
    > >> 2) If the bridge drivers are loaded as modules, I have a feeling they will be
    > >> loaded sequentially and therefore the order of the bridges would only change
    > >> if the order of the loading of the drivers changed.
    > >
    > > And this is a major problem when it comes to multiple bridges of differing
    > > types. What I'm saying is that this patch simply fixes this one problematic
    > > case. We can move this out as soon as we have a more robust implementation.
    > >
    > > As of now however, I think applying this is useful as we have a decent
    > > workaround to the problem. If you want I can make the fact of it being
    > > applicable only to cases with differing bridges explicit in the commit
    > > message.
    > >
    >
    > The problem is, I'm not convinced that this is the correct approach to take. I
    > think this should be parsed from sysfs dynamically (which may require some
    > work). I shall use the ethernet devices on my machine as an example:
    >
    > I have 2 ethernet devices (and lo) on my machine:
    >
    > $ ls /sys/class/net/
    > eth0 eth1 lo
    > $
    >
    > These are symlinks and I can quite quickly find out which each of these
    > devices in (based on topology):
    > $ ls -l /sys/class/net/
    > total 0
    > lrwxrwxrwx 1 root root 0 2011-08-10 11:56 eth0 ->
    > ../../devices/pci0000:00/0000:00:19.0/net/eth0
    > lrwxrwxrwx 1 root root 0 2011-08-10 11:56 eth1 ->
    > ../../devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/eth1
    > lrwxrwxrwx 1 root root 0 2011-08-10 11:56 lo -> ../../devices/virtual/net/lo
    > $
    >
    > I'd think that this contains the information that you have in the config file
    > (based on the previous discussion we had) and would allow you to map the bus
    > numbering after booting.
    >
    > To do this, I think we need to register a class called "vme", I guess in
    > vme_init() and add a call to class_device_register in vme_register_bridge and
    > a call to class_device_unregister in vme_unregister_bridge.
    >
    > Greg: Is that right?

    Yes.

    > I'm really not convinced that the solution presented in this patch is suitable
    > for inclusion upstream.

    I agree. Bus numbers are dynamic and should NEVER be depended on by
    userspace to be static and unchanging on reboots.

    thanks,

    greg k-h


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