On Wed, 9 Oct 2019, Bastien Nocera wrote:
> The kernel currenly has only 2 usb_device_drivers, one generic one, one
> that completely replaces the generic one to make USB devices usable over
> a network.
Presumably your first driver is in generic.c. Where is the second one?
> Use the newly exported generic driver functions when a driver declares
> to want them run, in addition to its own code. This makes it possible to
> write drivers that extend the generic USB driver.
>
> Signed-off-by: Bastien Nocera <hadess@xxxxxxxxxx>
This has a few problems. The biggest one is that the device core does
not guarantee any order of driver probing. If generic.c is probed
first, the subclass driver will never get probed -- which is a pretty
fatal flaw.
> ---
> drivers/usb/core/driver.c | 36 ++++++++++++++++++++++++++++++------
> include/linux/usb.h | 1 +
> 2 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index 2b27d232d7a7..863e380a272b 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -261,10 +261,17 @@ static int usb_probe_device(struct device *dev)
> */
> if (!udriver->supports_autosuspend)
> error = usb_autoresume_device(udev);
> + if (error)
> + return error;
>
> - if (!error)
> - error = udriver->probe(udev);
> - return error;
> + if (udriver->generic_init)
> + error = usb_generic_driver_probe(udev);
> + if (error)
> + return error;
> +
> + if (udriver->probe)
> + return udriver->probe(udev);
> + return 0;
> }
>
> /* called from driver core with dev locked */
> @@ -273,7 +280,10 @@ static int usb_unbind_device(struct device *dev)
> struct usb_device *udev = to_usb_device(dev);
> struct usb_device_driver *udriver = to_usb_device_driver(dev->driver);
>
> - udriver->disconnect(udev);
> + if (udriver->generic_init)
> + usb_generic_driver_disconnect(udev);
> + if (udriver->disconnect)
> + udriver->disconnect(udev);
The order is wrong. The disconnects should always be done in reverse
order of probing. This is true whenever you have a destructor for a
subclass; the subclasses destructor runs before the superclass's
destructor.
> if (!udriver->supports_autosuspend)
> usb_autosuspend_device(udev);
> return 0;
> @@ -886,6 +896,14 @@ int usb_register_device_driver(struct usb_device_driver *new_udriver,
> if (usb_disabled())
> return -ENODEV;
>
> + if (new_udriver->probe == NULL &&
> + !new_udriver->generic_init) {
There's no point adding this extra test. Even subclass drivers should
have a probe function.
> + printk(KERN_ERR "%s: error %d registering device "
> + " driver %s, no probe() function\n",
Don't split character strings. They are an exception to the 80-column
limit.
> + usbcore_name, retval, new_udriver->name);
> + return -EINVAL;
> + }
> +
> new_udriver->drvwrap.for_devices = 1;
> new_udriver->drvwrap.driver.name = new_udriver->name;
> new_udriver->drvwrap.driver.bus = &usb_bus_type;
> @@ -1149,7 +1167,10 @@ static int usb_suspend_device(struct usb_device *udev, pm_message_t msg)
> udev->do_remote_wakeup = 0;
> udriver = &usb_generic_driver;
> }
> - status = udriver->suspend(udev, msg);
> + if (udriver->generic_init)
> + status = usb_generic_driver_suspend (udev, msg);
> + if (status == 0 && udriver->suspend)
> + status = udriver->suspend(udev, msg);
Again, the order is wrong. Suspend the subclass driver first.
> done:
> dev_vdbg(&udev->dev, "%s: status %d\n", __func__, status);
> @@ -1181,7 +1202,10 @@ static int usb_resume_device(struct usb_device *udev, pm_message_t msg)
> udev->reset_resume = 1;
>
> udriver = to_usb_device_driver(udev->dev.driver);
> - status = udriver->resume(udev, msg);
> + if (udriver->generic_init)
> + status = usb_generic_driver_resume (udev, msg);
> + if (status == 0 && udriver->resume)
> + status = udriver->resume(udev, msg);
>
> done:
> dev_vdbg(&udev->dev, "%s: status %d\n", __func__, status);
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index e656e7b4b1e4..fb9ad3511e55 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -1242,6 +1242,7 @@ struct usb_device_driver {
> const struct attribute_group **dev_groups;
> struct usbdrv_wrap drvwrap;
> unsigned int supports_autosuspend:1;
> + unsigned int generic_init:1;
How about using a name that actually says something about the driver?
Such as generic_subclass? Or subclass_of_generic?
"init" has nothing to do with anything.
> };
> #define to_usb_device_driver(d) container_of(d, struct usb_device_driver, \
> drvwrap.driver)
Alan Stern
