On Wed, 5 Jan 2011, Sarah Sharp wrote: > I think I'm hearing you want some of the shared_hcd references to go > away, with the eventual goal of perhaps getting rid of the pointer out > of the usb_hcd entirely. I agree that dead code like the SAW_IRQ flag > and the check_root_hub_suspended() code should go away, but I don't > think we can get rid of shared_hcd entirely. Yeah, that's what I'd like. Since you still feel you need it, go ahead and redo the RFC using the other changes we discussed and keep the shared_hcd pointer. Afterward we can go through and figure out how to eliminate it (or even whether it _should_ be eliminated). > You've addressed the use cases in the suspend and resume path, but > there's still an issue with the allocation and freeing. If you agree > that the shared roothub allocation should go in the PCI core because of > the shared resource visibility issue, Refresh my memory: What is the shared resource visibility issue? It's probably sitting in an old email message somewhere, but so many of them have gone by that I can't put my finger on it. > then the PCI core needs to also > deallocate the shared_hcd. How do you propose to do that when the USB > PCI core doesn't have a reference to the non-primary usb_hcd? > usb_hcd_pci_remove() needs to have a pointer to call usb_put_hcd() with. > > Also, in digging around the deallocation path, I found another design > decision I made based on shared_hcd being a part of usb_hcd. Right now, > the shared_hcd pointer is acting like a reference count on the bandwidth > mutex: ... > If the USB core has no notion of whether a shared roothub is allocated > (which you seem to be advocating for by making the xHCI driver call into > usb_hcd_pci_probe() and then allocating the shared_hcd), then the USB > core has no idea when to deallocate shared resources. That's simple. You allocate the primary hcd first (along with all the necessary resources) in the usual way by calling usb_hcd_pci_probe, and then you add the secondary hcd, letting it share the primary's resources (usb_add_shared_hcd). When it's time for the driver to be unloaded, you deallocate the secondary hcd (usb_remove_shared_hcd) leaving the shared resources intact, and then you deallocate the primary hcd by calling usb_hcd_pci_remove normally. In other words, you reverse the actions taken during the original registration. This also handles the problem of the bandwidth mutex; it gets treated like all the other shared resources. hcd_release can simply do: if (primary_hcd(hcd)) kfree(hcd->bandwidth_mutex); Alan Stern -- 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
