| Message ID | 20221212152035.31806-1-johan@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] USB: fix misleading usb_set_intfdata() kernel doc | expand |
On Tue. 13 Dec. 2022 at 00:20, Johan Hovold <johan@kernel.org> wrote: > The struct device driver-data pointer is used for any data that a driver > may need in various callbacks while bound to the device. For > convenience, subsystems typically provide wrappers such as > usb_set_intfdata() of the generic accessor functions for use in bus > callbacks. > > There is generally no longer any need for a driver to clear the pointer, > but since commit 0998d0631001 ("device-core: Ensure drvdata = NULL when > no driver is bound") the driver-data pointer is set to NULL by driver > core post unbind anyway. > > For historical reasons, USB core also clears this pointer when an > explicitly claimed interface is released. > > Due to a misunderstanding, a misleading kernel doc comment for > usb_set_intfdata() was recently added which claimed that the driver data > pointer must not be cleared during disconnect before "all actions [are] > completed", which is both imprecise and incorrect. > > Specifically, drivers like cdc-acm which claim additional interfaces use > the driver-data pointer as a flag which is cleared when the first > interface is unbound. As long as a driver does not do something odd like > dereference the pointer in, for example, completion callbacks, this can > be done at any time during disconnect. And in any case this is no > different than for any other resource, like the driver data itself, > which may be freed by the disconnect callback. > > Note that the comment actually also claimed that the interface itself > was somehow being set to NULL by driver core. > > Fix the kernel doc by removing incorrect, overly specific and misleading > details and adding a comment about why some drivers do clear the > driver-data pointer. > > Fixes: 27ef17849779 ("usb: add usb_set_intfdata() documentation") > Signed-off-by: Johan Hovold <johan@kernel.org> Thank you for fixing my mess :) Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Yours sincerely, Vincent Mailhol
diff --git a/include/linux/usb.h b/include/linux/usb.h index b47371d44d1b..8a32e17f826e 100644 --- a/include/linux/usb.h +++ b/include/linux/usb.h @@ -267,16 +267,15 @@ static inline void *usb_get_intfdata(struct usb_interface *intf) } /** - * usb_set_intfdata() - associate driver-specific data with the interface - * @intf: the usb interface - * @data: pointer to the device priv structure or %NULL + * usb_set_intfdata() - associate driver-specific data with an interface + * @intf: USB interface + * @data: driver data * - * Drivers should use this function in their probe() to associate their - * driver-specific data with the usb interface. + * Drivers can use this function in their probe() callbacks to associate + * driver-specific data with an interface. * - * When disconnecting, the core will take care of setting @intf back to %NULL, - * so no actions are needed on the driver side. The interface should not be set - * to %NULL before all actions completed (e.g. no outsanding URB remaining). + * Note that there is generally no need to clear the driver-data pointer even + * if some drivers do so for historical or implementation-specific reasons. */ static inline void usb_set_intfdata(struct usb_interface *intf, void *data) {
The struct device driver-data pointer is used for any data that a driver may need in various callbacks while bound to the device. For convenience, subsystems typically provide wrappers such as usb_set_intfdata() of the generic accessor functions for use in bus callbacks. There is generally no longer any need for a driver to clear the pointer, but since commit 0998d0631001 ("device-core: Ensure drvdata = NULL when no driver is bound") the driver-data pointer is set to NULL by driver core post unbind anyway. For historical reasons, USB core also clears this pointer when an explicitly claimed interface is released. Due to a misunderstanding, a misleading kernel doc comment for usb_set_intfdata() was recently added which claimed that the driver data pointer must not be cleared during disconnect before "all actions [are] completed", which is both imprecise and incorrect. Specifically, drivers like cdc-acm which claim additional interfaces use the driver-data pointer as a flag which is cleared when the first interface is unbound. As long as a driver does not do something odd like dereference the pointer in, for example, completion callbacks, this can be done at any time during disconnect. And in any case this is no different than for any other resource, like the driver data itself, which may be freed by the disconnect callback. Note that the comment actually also claimed that the interface itself was somehow being set to NULL by driver core. Fix the kernel doc by removing incorrect, overly specific and misleading details and adding a comment about why some drivers do clear the driver-data pointer. Fixes: 27ef17849779 ("usb: add usb_set_intfdata() documentation") Signed-off-by: Johan Hovold <johan@kernel.org> --- Changes in v2 - fix up rather than drop the comment include/linux/usb.h | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)