Re: [PATCH v20 3/5] usb: misc: Add onboard_usb_hub driver

Greg Kroah-Hartman
2022-02-08T11:31:58Z

On Wed, Jan 19, 2022 at 12:43:43PM -0800, Matthias Kaehlcke wrote:
> The main issue this driver addresses is that a USB hub needs to be
> powered before it can be discovered. For discrete onboard hubs (an
> example for such a hub is the Realtek RTS5411) this is often solved
> by supplying the hub with an 'always-on' regulator, which is kind
> of a hack. Some onboard hubs may require further initialization
> steps, like changing the state of a GPIO or enabling a clock, which
> requires even more hacks. This driver creates a platform device
> representing the hub which performs the necessary initialization.
> Currently it only supports switching on a single regulator, support
> for multiple regulators or other actions can be added as needed.
> Different initialization sequences can be supported based on the
> compatible string.
>
> Besides performing the initialization the driver can be configured
> to power the hub off during system suspend. This can help to extend
> battery life on battery powered devices which have no requirements
> to keep the hub powered during suspend. The driver can also be
> configured to leave the hub powered when a wakeup capable USB device
> is connected when suspending, and power it off otherwise.
>
> Technically the driver consists of two drivers, the platform driver
> described above and a very thin USB driver that subclasses the
> generic driver. The purpose of this driver is to provide the platform
> driver with the USB devices corresponding to the hub(s) (a hub
> controller may provide multiple 'logical' hubs, e.g. one to support
> USB 2.0 and another for USB 3.x).
>
> Note: the current series only supports hubs connected directly to
> a root hub, support for other configurations could be added if
> needed.
>
> Co-developed-by: Ravi Chandra Sadineni <ravisadineni@chromium.org>
> Signed-off-by: Ravi Chandra Sadineni <ravisadineni@chromium.org>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> Acked-by: Alan Stern <stern@rowland.harvard.edu>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> Changes in v20:
> - s/nontrivial/non-trivial/ in Kconfig doc
> - added include of 'export.h'
> - initialize variable 'power_off' in onboard_hub_suspend() at
> declaration time
> - renamed set_udev_link_name() to get_udev_link_name()
> - use kzalloc to allocate struct usbdev_node instead of devm_kzalloc()
> - release the lock in onboard_hub_add_usbdev() before calling
> get_udev_link_name()
> - free struct usbdev_node in onboard_hub_remove_usbdev(), now that
> it doesn't used managed memory
> - make struct onboard_hub const in always_powered_in_suspend_show()
> - call put_device() if pdev is not bound in _find_onboard_hub()
> - get driver data before calling put_device() in _find_onboard_hub()
> - log platform device name when sysfs link creation fails in
> onboard_hub_usbdev_probe()
> - added kernel doc for onboard_hub_create_pdevs() and
> onboard_hub_destroy_pdevs()
> - added 'Reviewed-by' tag from Doug
>
> Changes in v19:
> - added VID:PID pairs and compatible strings for RTS5414 hub
> - updated comments with RTS5411 USB versions to reflect those
> reported/supported by the hub
>
> Changes in v18:
> - introduced hidden Kconfig option to align module vs. builtin
> choice with CONFIG_USB (thanks Doug!)
> - refactored onboard_hub_create_pdevs()
>
> Changes in v17:
> - updated date and kernel version in ABI documentation for
> 'always_powered_in_suspend' attribute
> - removed obsolete .yaml entry from MAINTAINERS file
> - added entry for ABI documentation to MAINTAINERS file
> - renamed struct 'udev_node' to 'usbdev_node'
> - changed return logic in onboard_hub_suspend/resume() to
> get rid of 'rc' variable
> - added helper set_udev_link_name() to set link names for
> onboard hub USB devices
> - use of_parse_phandle() instead of of_property_read_u32() +
> of_find_node_by_phandle() combo
> - defer probing in _find_onboard_hub() if the platform device
> isn't bound yet
> - initialize list head passed as parameter to
> onboard_hub_create_pdevs() instead of relying on the caller
> to do so
> - don't require the 'companion-hub' property to be specified.
> This is needed to support hubs without companion hub
> - use devm_kzalloc() to allocate platform device list entries
> and stop freeing them explicitly
> - remove unnecessary INIT_LIST_HEAD() of platform device list
> entries
> - use '%pOF' to print DT node name
> - delete platform device list entries from the list of devices
> in onboard_hub_destroy_pdevs(). It shouldn't be strictly
> necessary, but better be on the safe side.
>
> Changes in v16:
> - none
>
> Changes in v15:
> - none
>
> Changes in v14:
> - none
>
> Changes in v13:
> - none
>
> Changes in v12:
> - use IS_ENABLED(CONFIG_USB_ONBOARD_HUB_MODULE) in onboard_hub.h to
> also check for the driver built as module
> - include onboard_hub.h again from the driver to make sure there are
> prototype declarations for the public functions
> - remove indentation from label in onboard_hub_create_pdevs()
>
> Changes in v11:
> - added onboard_hub_create/destroy_pdevs() helpers, to support multiple onboard
> hubs connected to the same parent hub
> - don't include ‘onboard_hub.h’ from the onboard hub driver
> - updated commit message
> - added ‘Acked-by' from Alan
>
> Changes in v10:
> - always use of_is_onboard_usb_hub() stub unless ONBOARD_USB_HUB=y/m
>
> Changes in v9:
> - none
>
> Changes in v8:
> - none
>
> Changes in v7:
> - don't declare stub for of_is_onboard_usb_hub() when
> CONFIG_COMPILE_TEST is defined
>
> Changes in v6:
> - use 'companion-hub' to locate the platform device, instead of
> scanning through the nodes of the parent
> - added ABI documentation for 'always_powered_in_suspend'
> - sysfs_emit() instead of sprintf() in always_powered_in_suspend_show()
> - register sysfs attribute through driver.dev_groups
> - evaluate return value of driver_attach() in _probe()
> - use dev_warn() instead of WARN_ON() in _probe()
> - include 'onboard_hub.h'
>
> Changes in v5:
> - the platform device is now instantiated from the same DT node
> as the 'primary' USB hub device
> - use the USB compatible strings for the platform device
> - refactored _find_onboard_hub() to search the parents child
> nodes for a platform device with a matching compatible string
> - added exported function of_is_onboard_usb_hub() to allow other
> drivers (like xhci_plat) to check if one of their child DT nodes
> is a supported hub
> - use late suspend to make sure info about wakeup enabled descendants
> is updated
> - call driver_attach() for the USB driver in onboard_hub_probe() to
> make sure the driver is re-attached after the device_release_driver()
> calls in onboard_hub_remove()
> - renamed sysfs attribute 'power_off_in_suspend' to
> 'always_powered_in_suspend'
> - added sysfs symlinks between platform device and USB devices
> - marked 'onboard_hub_pm_ops' as __maybe_unused
> - removed 'realtek' compatible string which is not needed at this
> point
> - fix log for regulator_disable() failure
>
> Changes in v4:
> - updated Kconfig documentation
> - changed the loop in onboard_hub_remove() to release the hub lock
> before unbinding the USB device and make self deadlock prevention
> less clunky
> - fixed return value in onboard_hub_usbdev_probe()
> - added entry to MAINTAINERS file
>
> Changes in v3:
> - updated the commit message
> - updated description in Kconfig
> - remove include of 'core/usb.h'
> - use 'is_powered_on' flag instead of 'has_wakeup_capable_descendants'
> - added 'going_away' flag to struct onboard_hub
> - don't allow adding new USB devices when the platform device is going away
> - don't bother with deleting the list item in onboard_hub_remove_usbdev()
> when the platform device is going away
> - don't assume in onboard_hub_suspend() that all USB hub devices are
> connected to the same controller
> - removed unnecessary devm_kfree() from onboard_hub_remove_usbdev()
> - fixed error handling in onboard_hub_remove_usbdev()
> - use kstrtobool() instead of strtobool() in power_off_in_suspend_store()
> - unbind USB devices in onboard_hub_remove() to avoid dangling references
> to the platform device
> - moved put_device() for platform device to _find_onboard_hub()
> - changed return value of onboard_hub_remove_usbdev() to void
> - evaluate return value of onboard_hub_add_usbdev()
> - register 'power_off_in_suspend' as managed device attribute
> - use USB_DEVICE macro instead manual initialization
> - add unwinding to onboard_hub_init()
> - updated MODULE_DESCRIPTION
> - use module_init() instead of device_initcall()
>
> Changes in v2:
> - check wakeup enabled state of the USB controller instead of
> using 'wakeup-source' property
> - use sysfs attribute instead of DT property to determine if
> the hub should be powered off at all during system suspend
> - added missing brace in onboard_hub_suspend()
> - updated commit message
> - use pm_ptr for pm_ops as suggested by Alan
>
> Changes in v1:
> - renamed the driver to 'onboard_usb_hub'
> - single file for platform and USB driver
> - USB hub devices register with the platform device
> - the DT includes a phandle of the platform device
> - the platform device now controls when power is turned off
> - the USB driver became a very thin subclass of the generic USB
> driver
> - enabled autosuspend support
>
> .../sysfs-bus-platform-onboard-usb-hub | 8 +
> MAINTAINERS | 7 +
> drivers/usb/misc/Kconfig | 23 +
> drivers/usb/misc/Makefile | 1 +
> drivers/usb/misc/onboard_usb_hub.c | 511 ++++++++++++++++++
> include/linux/usb/onboard_hub.h | 18 +
> 6 files changed, 568 insertions(+)
> create mode 100644 Documentation/ABI/testing/sysfs-bus-platform-onboard-usb-hub
> create mode 100644 drivers/usb/misc/onboard_usb_hub.c
> create mode 100644 include/linux/usb/onboard_hub.h
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-platform-onboard-usb-hub b/Documentation/ABI/testing/sysfs-bus-platform-onboard-usb-hub
> new file mode 100644
> index 000000000000..39fa2ed29fed
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-platform-onboard-usb-hub
> @@ -0,0 +1,8 @@
> +What: /sys/bus/platform/devices/<dev>/always_powered_in_suspend
> +Date: November 2021
> +KernelVersion: 5.17
> +Contact: Matthias Kaehlcke <matthias@kaehlcke.net>
> + linux-usb@vger.kernel.org
> +Description:
> + (RW) Controls whether the USB hub remains always powered
> + during system suspend or not.
> \ No newline at end of file
> diff --git a/MAINTAINERS b/MAINTAINERS
> index dd36acc87ce6..68bc6efaad3f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -14183,6 +14183,13 @@ S: Maintained
> T: git git://linuxtv.org/media_tree.git
> F: drivers/media/i2c/ov9734.c
>
> +ONBOARD USB HUB DRIVER
> +M: Matthias Kaehlcke <mka@chromium.org>
> +L: linux-usb@vger.kernel.org
> +S: Maintained
> +F: Documentation/ABI/testing/sysfs-bus-platform-onboard-usb-hub
> +F: drivers/usb/misc/onboard_usb_hub.c
> +
> ONENAND FLASH DRIVER
> M: Kyungmin Park <kyungmin.park@samsung.com>
> L: linux-mtd@lists.infradead.org
> diff --git a/drivers/usb/misc/Kconfig b/drivers/usb/misc/Kconfig
> index 8f1144359012..99bc262a41f6 100644
> --- a/drivers/usb/misc/Kconfig
> +++ b/drivers/usb/misc/Kconfig
> @@ -284,3 +284,26 @@ config BRCM_USB_PINMAP
> This option enables support for remapping some USB external
> signals, which are typically on dedicated pins on the chip,
> to any gpio.
> +
> +config USB_ONBOARD_HUB
> + bool "Onboard USB hub support"
> + depends on OF || COMPILE_TEST
> + help
> + Say Y here if you want to support discrete onboard USB hubs that
> + don't require an additional control bus for initialization, but
> + need some non-trivial form of initialization, such as enabling a
> + power regulator. An example for such a hub is the Realtek
> + RTS5411.
> +
> + This driver can be used as a module but its state (module vs
> + builtin) must match the state of the USB subsystem. Enabling
> + this config will enable the driver and it will automatically
> + match the state of the USB subsystem. If this driver is a
> + module it will be called onboard_usb_hub.
> +
> +if USB_ONBOARD_HUB
> +config USB_ONBOARD_HUB_ACTUAL
> + tristate
> + default m if USB=m
> + default y if USB=y
> +endif
> diff --git a/drivers/usb/misc/Makefile b/drivers/usb/misc/Makefile
> index 5f4e598573ab..9549b88c2cc1 100644
> --- a/drivers/usb/misc/Makefile
> +++ b/drivers/usb/misc/Makefile
> @@ -32,3 +32,4 @@ obj-$(CONFIG_USB_CHAOSKEY) += chaoskey.o
> obj-$(CONFIG_USB_SISUSBVGA) += sisusbvga/
> obj-$(CONFIG_USB_LINK_LAYER_TEST) += lvstest.o
> obj-$(CONFIG_BRCM_USB_PINMAP) += brcmstb-usb-pinmap.o
> +obj-$(CONFIG_USB_ONBOARD_HUB_ACTUAL) += onboard_usb_hub.o
> diff --git a/drivers/usb/misc/onboard_usb_hub.c b/drivers/usb/misc/onboard_usb_hub.c
> new file mode 100644
> index 000000000000..e280409aecf5
> --- /dev/null
> +++ b/drivers/usb/misc/onboard_usb_hub.c
> @@ -0,0 +1,511 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Driver for onboard USB hubs
> + *
> + * Copyright (c) 2022, Google LLC
> + */
> +
> +#include <linux/device.h>
> +#include <linux/export.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/list.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/suspend.h>
> +#include <linux/sysfs.h>
> +#include <linux/usb.h>
> +#include <linux/usb/hcd.h>
> +#include <linux/usb/of.h>
> +#include <linux/usb/onboard_hub.h>
> +
> +static struct usb_device_driver onboard_hub_usbdev_driver;
> +
> +/************************** Platform driver **************************/
> +
> +struct usbdev_node {
> + struct usb_device *udev;
> + struct list_head list;
> +};
> +
> +struct onboard_hub {
> + struct regulator *vdd;
> + struct device *dev;
> + bool always_powered_in_suspend;
> + bool is_powered_on;
> + bool going_away;
> + struct list_head udev_list;
> + struct mutex lock;
> +};
> +
> +static int onboard_hub_power_on(struct onboard_hub *hub)
> +{
> + int err;
> +
> + err = regulator_enable(hub->vdd);
> + if (err) {
> + dev_err(hub->dev, "failed to enable regulator: %d\n", err);
> + return err;
> + }
> +
> + hub->is_powered_on = true;
> +
> + return 0;
> +}
> +
> +static int onboard_hub_power_off(struct onboard_hub *hub)
> +{
> + int err;
> +
> + err = regulator_disable(hub->vdd);
> + if (err) {
> + dev_err(hub->dev, "failed to disable regulator: %d\n", err);
> + return err;
> + }
> +
> + hub->is_powered_on = false;
> +
> + return 0;
> +}
> +
> +static int __maybe_unused onboard_hub_suspend(struct device *dev)
> +{
> + struct onboard_hub *hub = dev_get_drvdata(dev);
> + struct usbdev_node *node;
> + bool power_off = true;
> +
> + if (hub->always_powered_in_suspend)
> + return 0;
> +
> + mutex_lock(&hub->lock);
> +
> + list_for_each_entry(node, &hub->udev_list, list) {
> + if (!device_may_wakeup(node->udev->bus->controller))
> + continue;
> +
> + if (usb_wakeup_enabled_descendants(node->udev)) {
> + power_off = false;
> + break;
> + }
> + }
> +
> + mutex_unlock(&hub->lock);
> +
> + if (!power_off)
> + return 0;
> +
> + return onboard_hub_power_off(hub);
> +}
> +
> +static int __maybe_unused onboard_hub_resume(struct device *dev)
> +{
> + struct onboard_hub *hub = dev_get_drvdata(dev);
> +
> + if (hub->is_powered_on)
> + return 0;
> +
> + return onboard_hub_power_on(hub);
> +}
> +
> +static inline void get_udev_link_name(const struct usb_device *udev, char *buf, size_t size)
> +{
> + snprintf(buf, size, "usb_dev.%s", dev_name(&udev->dev));
> +}
> +
> +static int onboard_hub_add_usbdev(struct onboard_hub *hub, struct usb_device *udev)
> +{
> + struct usbdev_node *node;
> + char link_name[64];
> + int err;
> +
> + mutex_lock(&hub->lock);
> +
> + if (hub->going_away) {
> + err = -EINVAL;
> + goto error;
> + }
> +
> + node = kzalloc(sizeof(*node), GFP_KERNEL);
> + if (!node) {
> + err = -ENOMEM;
> + goto error;
> + }
> +
> + node->udev = udev;
> +
> + list_add(&node->list, &hub->udev_list);
> +
> + mutex_unlock(&hub->lock);
> +
> + get_udev_link_name(udev, link_name, sizeof(link_name));
> + WARN_ON(sysfs_create_link(&hub->dev->kobj, &udev->dev.kobj, link_name));
> +
> + return 0;
> +
> +error:
> + mutex_unlock(&hub->lock);
> +
> + return err;
> +}
> +
> +static void onboard_hub_remove_usbdev(struct onboard_hub *hub, const struct usb_device *udev)
> +{
> + struct usbdev_node *node;
> + char link_name[64];
> +
> + get_udev_link_name(udev, link_name, sizeof(link_name));
> + sysfs_remove_link(&hub->dev->kobj, link_name);
> +
> + mutex_lock(&hub->lock);
> +
> + list_for_each_entry(node, &hub->udev_list, list) {
> + if (node->udev == udev) {
> + list_del(&node->list);
> + kfree(node);
> + break;
> + }
> + }
> +
> + mutex_unlock(&hub->lock);
> +}
> +
> +static ssize_t always_powered_in_suspend_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + const struct onboard_hub *hub = dev_get_drvdata(dev);
> +
> + return sysfs_emit(buf, "%d\n", hub->always_powered_in_suspend);
> +}
> +
> +static ssize_t always_powered_in_suspend_store(struct device *dev, struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct onboard_hub *hub = dev_get_drvdata(dev);
> + bool val;
> + int ret;
> +
> + ret = kstrtobool(buf, &val);
> + if (ret < 0)
> + return ret;
> +
> + hub->always_powered_in_suspend = val;
> +
> + return count;
> +}
> +static DEVICE_ATTR_RW(always_powered_in_suspend);
> +
> +static struct attribute *onboard_hub_attrs[] = {
> + &dev_attr_always_powered_in_suspend.attr,
> + NULL,
> +};
> +ATTRIBUTE_GROUPS(onboard_hub);
> +
> +static int onboard_hub_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct onboard_hub *hub;
> + int err;
> +
> + hub = devm_kzalloc(dev, sizeof(*hub), GFP_KERNEL);
> + if (!hub)
> + return -ENOMEM;
> +
> + hub->vdd = devm_regulator_get(dev, "vdd");
> + if (IS_ERR(hub->vdd))
> + return PTR_ERR(hub->vdd);
> +
> + hub->dev = dev;
> + mutex_init(&hub->lock);
> + INIT_LIST_HEAD(&hub->udev_list);
> +
> + dev_set_drvdata(dev, hub);
> +
> + err = onboard_hub_power_on(hub);
> + if (err)
> + return err;
> +
> + /*
> + * The USB driver might have been detached from the USB devices by
> + * onboard_hub_remove(), make sure to re-attach it if needed.
> + */
> + err = driver_attach(&onboard_hub_usbdev_driver.drvwrap.driver);
> + if (err) {
> + onboard_hub_power_off(hub);
> + return err;
> + }
> +
> + return 0;
> +}
> +
> +static int onboard_hub_remove(struct platform_device *pdev)
> +{
> + struct onboard_hub *hub = dev_get_drvdata(&pdev->dev);
> + struct usbdev_node *node;
> + struct usb_device *udev;
> +
> + hub->going_away = true;
> +
> + mutex_lock(&hub->lock);
> +
> + /* unbind the USB devices to avoid dangling references to this device */
> + while (!list_empty(&hub->udev_list)) {
> + node = list_first_entry(&hub->udev_list, struct usbdev_node, list);
> + udev = node->udev;
> +
> + /*
> + * Unbinding the driver will call onboard_hub_remove_usbdev(),
> + * which acquires hub->lock. We must release the lock first.
> + */
> + get_device(&udev->dev);
> + mutex_unlock(&hub->lock);
> + device_release_driver(&udev->dev);
> + put_device(&udev->dev);
> + mutex_lock(&hub->lock);
> + }
> +
> + mutex_unlock(&hub->lock);
> +
> + return onboard_hub_power_off(hub);
> +}
> +
> +static const struct of_device_id onboard_hub_match[] = {
> + { .compatible = "usbbda,411" },
> + { .compatible = "usbbda,5411" },
> + { .compatible = "usbbda,414" },
> + { .compatible = "usbbda,5414" },
> + {}
> +};
> +MODULE_DEVICE_TABLE(of, onboard_hub_match);
> +
> +static bool of_is_onboard_usb_hub(const struct device_node *np)
> +{
> + return !!of_match_node(onboard_hub_match, np);
> +}
> +
> +static const struct dev_pm_ops __maybe_unused onboard_hub_pm_ops = {
> + SET_LATE_SYSTEM_SLEEP_PM_OPS(onboard_hub_suspend, onboard_hub_resume)
> +};
> +
> +static struct platform_driver onboard_hub_driver = {
> + .probe = onboard_hub_probe,
> + .remove = onboard_hub_remove,
> +
> + .driver = {
> + .name = "onboard-usb-hub",
> + .of_match_table = onboard_hub_match,
> + .pm = pm_ptr(&onboard_hub_pm_ops),
> + .dev_groups = onboard_hub_groups,
> + },
> +};
> +
> +/************************** USB driver **************************/
> +
> +#define VENDOR_ID_REALTEK 0x0bda
> +
> +/*
> + * Returns the onboard_hub platform device that is associated with the USB
> + * device passed as parameter.
> + */
> +static struct onboard_hub *_find_onboard_hub(struct device *dev)
> +{
> + struct platform_device *pdev;
> + struct device_node *np;
> + struct onboard_hub *hub;
> +
> + pdev = of_find_device_by_node(dev->of_node);
> + if (!pdev) {
> + np = of_parse_phandle(dev->of_node, "companion-hub", 0);
> + if (!np) {
> + dev_err(dev, "failed to find device node for companion hub\n");
> + return ERR_PTR(-EINVAL);
> + }
> +
> + pdev = of_find_device_by_node(np);
> + of_node_put(np);
> +
> + if (!pdev || !device_is_bound(&pdev->dev)) {

I don't understand why you need to call device_is_bound() here. What
are you wanting to find here?

You found the hub device associated to this usb device, based on the
of_find_device_by_node() call, so why check it again? What could have
happened that this isn't the correct device?

> + if (pdev)
> + put_device(&pdev->dev);
> +
> + return ERR_PTR(-EPROBE_DEFER);

What are you deferring to have happen later?

> + }
> + }
> +
> + hub = dev_get_drvdata(&pdev->dev);
> + put_device(&pdev->dev);
> +
> + return hub;
> +}
> +
> +static int onboard_hub_usbdev_probe(struct usb_device *udev)
> +{
> + struct device *dev = &udev->dev;
> + struct onboard_hub *hub;
> + int err;
> +
> + /* ignore supported hubs without device tree node */
> + if (!dev->of_node)
> + return -ENODEV;
> +
> + hub = _find_onboard_hub(dev);
> + if (IS_ERR(hub))
> + return PTR_ERR(hub);
> +
> + dev_set_drvdata(dev, hub);
> +
> + err = onboard_hub_add_usbdev(hub, udev);
> + if (err)
> + return err;
> +
> + err = sysfs_create_link(&udev->dev.kobj, &hub->dev->kobj, "onboard_hub_dev");

What is this link for? Messing with sysfs links is a pain and drivers
really shouldn't be doing them if at all possible.

> + if (err)
> + dev_warn(&udev->dev, "failed to create symlink to platform device '%s'): %d\n",
> + dev_name(hub->dev), err);
> +
> + return 0;

So you ignore the error? That's fine, just odd.

> +}
> +
> +static void onboard_hub_usbdev_disconnect(struct usb_device *udev)
> +{
> + struct onboard_hub *hub = dev_get_drvdata(&udev->dev);
> +
> + sysfs_remove_link(&udev->dev.kobj, "onboard_hub_dev");
> +
> + onboard_hub_remove_usbdev(hub, udev);
> +}

thanks,

greg k-h