linux-kernel - Re: [PATCH 09/10] usb: Add USB subsystem notifications [ver #3]

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Date:   Tue, 11 Jun 2019 09:28:15 +0300
From:   Felipe Balbi <felipe.balbi@...ux.intel.com>
To:     Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Howells <dhowells@...hat.com>, viro@...iv.linux.org.uk,
        linux-usb@...r.kernel.org, raven@...maw.net,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-block@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] usb: Add USB subsystem notifications [ver #3]


Hi,

Alan Stern <stern@...land.harvard.edu> writes:
>> Greg Kroah-Hartman <gregkh@...uxfoundation.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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