On Tue, May 13, 2014 at 03:55:30PM -0700, Greg KH wrote:
> On Tue, May 13, 2014 at 12:58:23PM -0700, Todd E Brandt wrote:
> > This patch creates a separate instance of the usb_address0 mutex for each host
> > controller, and attaches it to the host controller device struct. This allows
> > devices on separate hosts to be enumerated in parallel; saving time.
> >
> > In the current code, there is a single, global instance of the usb_address0
> > mutex which is used for all devices on any host. This isn't completely
> > necessary, as this mutex is only needed to prevent address0 collisions for
> > devices on the *same* host (usb 2.0 spec, sec 4.6.1). This superfluous coverage
> > can cause additional delay in system resume on systems with multiple hosts
> > (up to several seconds depending on what devices are attached).
> >
> > For instance, if I have a USB WLAN and a KVM switch attached to two ports,
> > there's a chance that they could be initialized at the same time (e.g. on
> > system resume). They would both be in the Default state and would be
> > responding to requests from the default address (address 00H). If they were
> > on the same host, there'd be no way of differentiating the two devices and thus
> > the mutex is needed. But on separate hosts there's no chance of collision.
> >
> > Signed-off-by: Todd Brandt <todd.e.brandt@xxxxxxxxxxxxxxx>
> > ---
> > drivers/usb/core/hcd.c | 15 +++++++++++++--
> > drivers/usb/core/hub.c | 6 ++----
> > include/linux/usb/hcd.h | 1 +
> > 3 files changed, 16 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> > index 9c4e292..b5d89eb 100644
> > --- a/drivers/usb/core/hcd.c
> > +++ b/drivers/usb/core/hcd.c
> > @@ -2452,9 +2452,18 @@ struct usb_hcd *usb_create_shared_hcd(const struct hc_driver *driver,
> > return NULL;
> > }
> > mutex_init(hcd->bandwidth_mutex);
> > + hcd->usb_address0_mutex =
> > + kmalloc(sizeof(*hcd->usb_address0_mutex), GFP_KERNEL);
> > + if (!hcd->usb_address0_mutex) {
> > + kfree(hcd);
> > + dev_dbg(dev, "hcd usb_address0 mutex alloc failed\n");
>
> No need to ever do a "allocation failed" message, as kmalloc would have
> just done that if it did fail.
I was just copying the code structure of the bandwidth_mutex for code
symmetry, but I'll resubmit a patch which removes this and makes the
mutex a static member of the hcd struct (per Alan's comments)
>
> thanks,
>
> greg k-h
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