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    SubjectRe: [PATCH 09/10] usb: Add USB subsystem notifications [ver #3]
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    Hi,

    Alan Stern <stern@rowland.harvard.edu> writes:
    >> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
    >> > On Thu, Jun 06, 2019 at 10:55:24AM -0400, Alan Stern wrote:
    >> >> On Thu, 6 Jun 2019, Greg Kroah-Hartman wrote:
    >> >>
    >> >> > On Thu, Jun 06, 2019 at 10:24:18AM -0400, Alan Stern wrote:
    >> >> > > On Thu, 6 Jun 2019, David Howells wrote:
    >> >> > >
    >> >> > > > Add a USB subsystem notification mechanism whereby notifications about
    >> >> > > > hardware events such as device connection, disconnection, reset and I/O
    >> >> > > > errors, can be reported to a monitoring process asynchronously.
    >> >> > >
    >> >> > > USB I/O errors covers an awfully large and vague field. Do we really
    >> >> > > want to include them? I'm doubtful.
    >> >> >
    >> >> > See the other patch on the linux-usb list that wanted to start adding
    >> >> > KOBJ_CHANGE notifications about USB "i/o errors".
    >> >>
    >> >> That patch wanted to add notifications only for enumeration failures
    >> >> (assuming you're talking about the patch from Eugeniu Rosca), not I/O
    >> >> errors in general.
    >> >
    >> > Yes, sorry, I was thinking that as a "I/O failed in enumeration" :)
    >> >
    >> >> > So for "severe" issues, yes, we should do this, but perhaps not for all
    >> >> > of the "normal" things we see when a device is yanked out of the system
    >> >> > and the like.
    >> >>
    >> >> Then what counts as a "severe" issue? Anything besides enumeration
    >> >> failure?
    >> >
    >> > Not that I can think of at the moment, other than the other recently
    >> > added KOBJ_CHANGE issue. I'm sure we have other "hard failure" issues
    >> > in the USB stack that people will want exposed over time.
    >>
    >> From an XHCI standpoint, Transaction Errors might be one thing. They
    >> happen rarely and are a strong indication that the bus itself is
    >> bad. Either bad cable, misbehaving PHYs, improper power management, etc.
    >
    > Don't you also get transaction errors if the user unplugs a device in
    > the middle of a transfer? That's not the sort of thing we want to sent
    > notifications about.

    Mathias, do we get Transaction Error if user removes cable during a
    transfer? I thought we would just get Port Status Change with CC bit
    cleared, no?

    --
    balbi
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