From 7dc0c55e9f302e7048e040ee4437437bbea1e2cd Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Thu, 20 May 2021 16:21:44 -0400 Subject: [PATCH] USB: UDC core: Add udc_async_callbacks gadget op The Gadget API has a theoretical race when a gadget driver is unbound. Although the pull-up is turned off before the driver's ->unbind callback runs, if the USB cable were to be unplugged at just the wrong moment there would be nothing to prevent the UDC driver from invoking the ->disconnect callback after the unbind has finished. In theory, other asynchronous callbacks could also happen during the time before the UDC driver's udc_stop routine is called, and the gadget driver would not be prepared to handle any of them. We need a way to tell UDC drivers to stop issuing asynchronous (that is, ->suspend, ->resume, ->disconnect, ->reset, or ->setup) callbacks at some point after the pull-up has been turned off and before the ->unbind callback runs. This patch adds a new ->udc_async_callbacks callback to the usb_gadget_ops structure for precisely this purpose, and it adds the corresponding support to the UDC core. Later patches in this series add support for udc_async_callbacks to several UDC drivers. Acked-by: Felipe Balbi Signed-off-by: Alan Stern Link: https://lore.kernel.org/r/20210520202144.GC1216852@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/udc/core.c | 49 +++++++++++++++++++++++++++++++++++ include/linux/usb/gadget.h | 1 + 2 files changed, 50 insertions(+) diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c index 493ff93f7dda..b7f0b1ebaaa8 100644 --- a/drivers/usb/gadget/udc/core.c +++ b/drivers/usb/gadget/udc/core.c @@ -1147,6 +1147,53 @@ static inline void usb_gadget_udc_set_speed(struct usb_udc *udc, gadget->ops->udc_set_speed(gadget, s); } +/** + * usb_gadget_enable_async_callbacks - tell usb device controller to enable asynchronous callbacks + * @udc: The UDC which should enable async callbacks + * + * This routine is used when binding gadget drivers. It undoes the effect + * of usb_gadget_disable_async_callbacks(); the UDC driver should enable IRQs + * (if necessary) and resume issuing callbacks. + * + * This routine will always be called in process context. + */ +static inline void usb_gadget_enable_async_callbacks(struct usb_udc *udc) +{ + struct usb_gadget *gadget = udc->gadget; + + if (gadget->ops->udc_async_callbacks) + gadget->ops->udc_async_callbacks(gadget, true); +} + +/** + * usb_gadget_disable_async_callbacks - tell usb device controller to disable asynchronous callbacks + * @udc: The UDC which should disable async callbacks + * + * This routine is used when unbinding gadget drivers. It prevents a race: + * The UDC driver doesn't know when the gadget driver's ->unbind callback + * runs, so unless it is told to disable asynchronous callbacks, it might + * issue a callback (such as ->disconnect) after the unbind has completed. + * + * After this function runs, the UDC driver must suppress all ->suspend, + * ->resume, ->disconnect, ->reset, and ->setup callbacks to the gadget driver + * until async callbacks are again enabled. A simple-minded but effective + * way to accomplish this is to tell the UDC hardware not to generate any + * more IRQs. + * + * Request completion callbacks must still be issued. However, it's okay + * to defer them until the request is cancelled, since the pull-up will be + * turned off during the time period when async callbacks are disabled. + * + * This routine will always be called in process context. + */ +static inline void usb_gadget_disable_async_callbacks(struct usb_udc *udc) +{ + struct usb_gadget *gadget = udc->gadget; + + if (gadget->ops->udc_async_callbacks) + gadget->ops->udc_async_callbacks(gadget, false); +} + /** * usb_udc_release - release the usb_udc struct * @dev: the dev member within usb_udc @@ -1361,6 +1408,7 @@ static void usb_gadget_remove_driver(struct usb_udc *udc) kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE); usb_gadget_disconnect(udc->gadget); + usb_gadget_disable_async_callbacks(udc); if (udc->gadget->irq) synchronize_irq(udc->gadget->irq); udc->driver->unbind(udc->gadget); @@ -1442,6 +1490,7 @@ static int udc_bind_to_driver(struct usb_udc *udc, struct usb_gadget_driver *dri driver->unbind(udc->gadget); goto err1; } + usb_gadget_enable_async_callbacks(udc); usb_udc_connect_control(udc); kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE); diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h index 8811eb96e5cc..75c7538e350a 100644 --- a/include/linux/usb/gadget.h +++ b/include/linux/usb/gadget.h @@ -325,6 +325,7 @@ struct usb_gadget_ops { void (*udc_set_speed)(struct usb_gadget *, enum usb_device_speed); void (*udc_set_ssp_rate)(struct usb_gadget *gadget, enum usb_ssp_rate rate); + void (*udc_async_callbacks)(struct usb_gadget *gadget, bool enable); struct usb_ep *(*match_ep)(struct usb_gadget *, struct usb_endpoint_descriptor *, struct usb_ss_ep_comp_descriptor *);