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.
thanks,
greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
