On Mon, 7 Mar 2011, Sarah Sharp wrote:
> Introduce the notion of a PCI device that may be associated with more than
> one USB host controller driver (struct usb_hcd). This patch is the start
> of the work to separate the xHCI host controller into two roothubs: a USB
> 3.0 roothub with SuperSpeed-only ports, and a USB 2.0 roothub with
> HS/FS/LS ports.
>
> One usb_hcd structure is designated to be the "primary HCD", and a pointer
> is added to the usb_hcd structure to keep track of that. A new function
> call, usb_hcd_is_primary_hcd() is added to check whether the USB hcd is
> marked as the primary HCD (or if it is not part of a roothub pair). To
> allow the USB core and xHCI driver to access either roothub in a pair, a
> "shared_hcd" pointer is added to the usb_hcd structure.
>
> Add a new function, usb_create_shared_hcd(), that does roothub allocation
> for paired roothubs. It will act just like usb_create_hcd() did if the
> primary_hcd pointer argument is NULL. If it is passed a non-NULL
> primary_hcd pointer, it sets usb_hcd->shared_hcd and usb_hcd->primary_hcd
> fields. It will also skip the bandwidth_mutex allocation, and set the
> secondary hcd's bandwidth_mutex pointer to the primary HCD's mutex.
>
> IRQs are only allocated once for the primary roothub.
>
> Introduce a new usb_hcd driver flag that indicates the host controller
> driver wants to create two roothubs. If the HCD_SHARED flag is set, then
> the USB core PCI probe methods will allocate a second roothub, and make
> sure that second roothub gets freed during rmmod and in initialization
> error paths.
...
> +/*
> + * Roothubs that share one PCI device must also share the bandwidth mutex.
> + * Don't deallocate the bandwidth_mutex until the last shared usb_hcd is
> + * deallocated.
> + *
> + * The first shared roothub that is released will set shared_hcd to NULL. The
> + * second shared roothub that is released (or a USB host controller driver that
> + * doesn't set up shared roothubs) will deallocate the bandwidth mutex.
> + */
> static void hcd_release (struct kref *kref)
> {
> struct usb_hcd *hcd = container_of (kref, struct usb_hcd, kref);
>
> - kfree(hcd->bandwidth_mutex);
> + if (hcd->shared_hcd)
> + hcd->shared_hcd->shared_hcd = NULL;
> + else
> + kfree(hcd->bandwidth_mutex);
> kfree(hcd);
> }
This is okay as it stands, but I wonder if it can be simplified. The
order in which the hcd structures are released doesn't matter, because
the bandwidth mutex won't be accessed after the root hubs are
unregistered. Hence the mutex can be deallocated when the primary hcd
is removed (since the primary hcd structure always has to be removed
last).
Or am I missing something?
Alan Stern
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