usb: core: added uevent for over-current

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Aug 31, 2018 at 10:14:19AM -0700, Jon Flatley wrote:
> After commit 1cbd53c8cd85 ("usb: core: introduce per-port over-current
> counters") usb ports expose a sysfs value 'over_current_count'
> to user space. This value on its own is not very useful as it requires
> manual polling.
> 
> As a solution, fire a udev event from the usb hub device that specifies
> the values 'OVER_CURRENT_PORT' and 'OVER_CURRENT_COUNT' that indicate
> the path of the usb port where the over-current event occurred and the
> value of 'over_current_count' in sysfs. Additionally, call
> sysfs_notify() so the sysfs value supports poll().
> 
> Signed-off-by: Jon Flatley <jflat@chromium.org>
> ---
>  drivers/usb/core/hub.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 65feedd69323..c986b0fc2daa 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -27,6 +27,7 @@
>  #include <linux/random.h>
>  #include <linux/pm_qos.h>
>  #include <linux/pm_dark_resume.h>
> +#include <linux/kobject.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/byteorder.h>
> @@ -5096,6 +5097,40 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
>  	usb_lock_port(port_dev);
>  }
>  
> +/* Handle notifying userspace about hub over-current events */
> +static void port_over_current_notify(struct usb_port *port_dev)
> +{
> +	static char *envp[] = { NULL, NULL, NULL };
> +	struct device *hub_dev;
> +	char *port_dev_path;
> +
> +	sysfs_notify(&port_dev->dev.kobj, NULL, "over_current_count");
> +
> +	hub_dev = port_dev->dev.parent;
> +
> +	if (!hub_dev)
> +		return;
> +
> +	port_dev_path = kobject_get_path(&port_dev->dev.kobj, GFP_KERNEL);
> +	if (!port_dev_path)
> +		return;
> +
> +	envp[0] = kasprintf(GFP_KERNEL, "OVER_CURRENT_PORT=%s", port_dev_path);
> +	if (!envp[0])
> +		return;
> +
> +	envp[1] = kasprintf(GFP_KERNEL, "OVER_CURRENT_COUNT=%u",
> +			port_dev->over_current_count);
> +	if (!envp[1])
> +		goto exit;
> +
> +	kobject_uevent_env(&hub_dev->kobj, KOBJ_CHANGE, envp);
> +
> +	kfree(envp[1]);
> +exit:
> +	kfree(envp[0]);
> +}
> +
>  static void port_event(struct usb_hub *hub, int port1)
>  		__must_hold(&port_dev->status_lock)
>  {
> @@ -5138,6 +5173,7 @@ static void port_event(struct usb_hub *hub, int port1)
>  	if (portchange & USB_PORT_STAT_C_OVERCURRENT) {
>  		u16 status = 0, unused;
>  		port_dev->over_current_count++;
> +		port_over_current_notify(port_dev);

When an overcurrent "event" happens, does it just stay overloaded for
long periods of time?  Would this flood the system with lots of kobject
messages, or is this rate-limited somehow?

Also, as this is a new user/kernel abi you are creating, it needs to be
documented somewhere.  Perhaps in the sysfs file information for this
attribute?

thanks,

greg k-h