Date: Sat, 5 May 2012 11:28:08 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
To: Martin Mokrejs <mmokrejs@fold.natur.cuni.cz>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Paul Bolle <pebolle@tiscali.nl>, <linux-usb@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] usb: also announce bcdDevice
In-Reply-To: <4FA54292.5000102@fold.natur.cuni.cz>
Message-ID: <Pine.LNX.4.44L0.1205051125220.3737-100000@netrider.rowland.org>
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On Sat, 5 May 2012, Martin Mokrejs wrote:

> Greg Kroah-Hartman wrote:
> > On Sat, May 05, 2012 at 02:14:43PM +0200, Martin Mokrejs wrote:
> >> Paul Bolle wrote:
> >>> Currently announce_device() does print the idVendor and idProduct values
> >>> but does not print the bcdDevice value. USB devices are accurately
> >>> identified by all three values. See, for instance, the USB storage
> >>> quirks which will only apply for a certain (range of) bcdDevice
> >>> value(s). So it seems useful to also print bcdDevice when announcing USB
> >>> devices.
> >>
> >> Could it also report negotiated speed? full-speed, high-speed, super-speed?
> > 
> > All of this, including the bcdDevice, can be found in sysfs.  So I don't
> > want to take this patch, otherwise we would be just adding more and more
> > to the kernel log.
> > 
> > If you programatically want to find this out, use libudev or listen to
> > the dbus messages for new devices, don't watch the kernel log messages.
> 
> Hmm, but when you go through your syslog/dmesg lines especially in case of
> USB devices which you swap in and out quite often, it is too late to lookup
> some file elsewhere which relates to *current* device. The information
> is lost already if you changed device meanwhile. You just realize USB disk
> disconnected but you have not way find out except from the log files what
> speed did it use. In case of USB3 devices capable of lower speeds it is
> quite important. Some just claim USB3 capabilities (on the package box)
> but in real, always end up at high-speed only.
> 
> For me testing several USB disks, USB to SATA bridges, host controllers,
> kernel command-lines ... it is way to much work. Having the USB debug
> enabled, especially XHCI_HCD_DEBUG gives on the other had too much output
> for daily use but as this is all stuff prone to fail somewhere and at some
> point I keep it enabled.
> 
> I don't think it clutters syslog nor that it adds significant extra size
> to the output. It would save people from enabling debug just because of this.
> And no, average linux user never never lookup sysfs nor use libudev, really.
> Still, the link speed is of interest to everybody fiddling with the stuff
> and wondering why the damn thing is so slow or why did it disconnect. It gives
> an answer or at least a hint.

But the kernel _already_ logs a message listing new USB devices along 
with their speed.  In fact, it does this even if the ANNOUNCE config 
option isn't set.

Alan Stern

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