Re: [PATCH] USB: mutual exclusion for EHCI init and port resets

On Wednesday 10 October 2007, Alan Stern wrote:
> This patch (as999) fixes a problem that sometimes shows up when host
> controller driver modules are loaded in the wrong order.  If ehci-hcd
> happens to initialize an EHCI controller while the companion OHCI or
> UHCI controller is in the middle of a port reset, the reset can fail
> and the companion may get very confused.  The patch adds an
> rw-semaphore and uses it to keep EHCI initialization and port resets
> mutually exclusive.
> 
> Signed-off-by: Alan Stern <[email protected]>
> CC: David Brownell <[email protected]>

ACK.


> 
> ---
> 
> Index: usb-2.6/drivers/usb/core/hcd.h
> ===================================================================
> --- usb-2.6.orig/drivers/usb/core/hcd.h
> +++ usb-2.6/drivers/usb/core/hcd.h
> @@ -19,6 +19,8 @@
>  
>  #ifdef __KERNEL__
>  
> +#include <linux/rwsem.h>
> +
>  /* This file contains declarations of usbcore internals that are mostly
>   * used or exposed by Host Controller Drivers.
>   */
> @@ -470,5 +472,9 @@ static inline void usbmon_urb_complete(s
>  		: (in_interrupt () ? "in_interrupt" : "can sleep"))
>  
>  
> -#endif /* __KERNEL__ */
> +/* This rwsem is for use only by the hub driver and ehci-hcd.
> + * Nobody else should touch it.
> + */
> +extern struct rw_semaphore ehci_cf_port_reset_rwsem;
>  
> +#endif /* __KERNEL__ */
> Index: usb-2.6/drivers/usb/core/hub.c
> ===================================================================
> --- usb-2.6.orig/drivers/usb/core/hub.c
> +++ usb-2.6/drivers/usb/core/hub.c
> @@ -125,6 +125,12 @@ MODULE_PARM_DESC(use_both_schemes,
>  		"try the other device initialization scheme if the "
>  		"first one fails");
>  
> +/* Mutual exclusion for EHCI CF initialization.  This interferes with
> + * port reset on some companion controllers.
> + */
> +DECLARE_RWSEM(ehci_cf_port_reset_rwsem);
> +EXPORT_SYMBOL_GPL(ehci_cf_port_reset_rwsem);
> +
>  
>  static inline char *portspeed(int portstatus)
>  {
> @@ -1579,6 +1585,11 @@ static int hub_port_reset(struct usb_hub
>  {
>  	int i, status;
>  
> +	/* Block EHCI CF initialization during the port reset.
> +	 * Some companion controllers don't like it when they mix.
> +	 */
> +	down_read(&ehci_cf_port_reset_rwsem);
> +
>  	/* Reset the port */
>  	for (i = 0; i < PORT_RESET_TRIES; i++) {
>  		status = set_port_feature(hub->hdev,
> @@ -1610,7 +1621,7 @@ static int hub_port_reset(struct usb_hub
>  			usb_set_device_state(udev, status
>  					? USB_STATE_NOTATTACHED
>  					: USB_STATE_DEFAULT);
> -			return status;
> +			goto done;
>  		}
>  
>  		dev_dbg (hub->intfdev,
> @@ -1623,6 +1634,8 @@ static int hub_port_reset(struct usb_hub
>  		"Cannot enable port %i.  Maybe the USB cable is bad?\n",
>  		port1);
>  
> + done:
> +	up_read(&ehci_cf_port_reset_rwsem);
>  	return status;
>  }
>  
> Index: usb-2.6/drivers/usb/host/ehci-hcd.c
> ===================================================================
> --- usb-2.6.orig/drivers/usb/host/ehci-hcd.c
> +++ usb-2.6/drivers/usb/host/ehci-hcd.c
> @@ -645,10 +645,18 @@ static int ehci_run (struct usb_hcd *hcd
>  	 * are explicitly handed to companion controller(s), so no TT is
>  	 * involved with the root hub.  (Except where one is integrated,
>  	 * and there's no companion controller unless maybe for USB OTG.)
> +	 *
> +	 * Turning on the CF flag will transfer ownership of all ports
> +	 * from the companions to the EHCI controller.  If any of the
> +	 * companions are in the middle of a port reset at the time, it
> +	 * could cause trouble.  Write-locking ehci_cf_port_reset_rwsem
> +	 * guarantees that no resets are in progress.
>  	 */
> +	down_write(&ehci_cf_port_reset_rwsem);
>  	hcd->state = HC_STATE_RUNNING;
>  	ehci_writel(ehci, FLAG_CF, &ehci->regs->configured_flag);
>  	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
> +	up_write(&ehci_cf_port_reset_rwsem);
>  
>  	temp = HC_VERSION(ehci_readl(ehci, &ehci->caps->hc_capbase));
>  	ehci_info (ehci,
> 



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