Re: [PATCH v3] usb: core: add sysfs entry for usb device state

[Greg Kroah-Hartman]

On Mon, Jun 05, 2023 at 09:55:28PM +0000, Roy Luo wrote:
> Expose usb device state to userland as the information is useful in
> detecting non-compliant setups and diagnosing enumeration failures.
> For example:
> - End-to-end signal integrity issues: the device would fail port reset
>   repeatedly and thus be stuck in POWERED state.
> - Charge-only cables (missing D+/D- lines): the device would never enter
>   POWERED state as the HC would not see any pullup.
> 
> What's the status quo?
> We do have error logs such as "Cannot enable. Maybe the USB cable is bad?"
> to flag potential setup issues, but there's no good way to expose them to
> userspace.
> 
> Why add a sysfs entry in struct usb_port instead of struct usb_device?
> The struct usb_device is not device_add() to the system until it's in
> ADDRESS state hence we would miss the first two states. The struct
> usb_port is a better place to keep the information because its life
> cycle is longer than the struct usb_device that is attached to the port.
> 
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202306042228.e532af6e-oliver.sang@xxxxxxxxx
> Signed-off-by: Roy Luo <royluo@xxxxxxxxxx>
> ---
> This patch comes directly from RFC v2 after being reviewed by Alan Stern
> Link: https://lore.kernel.org/all/20230531010134.1092942-1-royluo@xxxxxxxxxx/
> More discussion about implementation options is in RFC v1
> Link: https://lore.kernel.org/all/20230525173818.219633-1-royluo@xxxxxxxxxx/
> 
> Changes since v1:
> * Address Alan Stern's comment: remove redundant NULL initializers in
>   update_port_device_state().
> 
> Changes since v2:
> * Fix "BUG: sleeping function called from invalid context" caught by
>   kernel test robot. Move sleeping function sysfs_get_dirent to port
>   initiailzation and keep the kernfs_node for future reference.
>   (Reviewed-by tag is reset as this patch involves more code changes)
> ---
>  Documentation/ABI/testing/sysfs-bus-usb |  9 +++++++
>  drivers/usb/core/hub.c                  | 15 ++++++++++++
>  drivers/usb/core/hub.h                  |  4 ++++
>  drivers/usb/core/port.c                 | 32 +++++++++++++++++++++----
>  4 files changed, 56 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
> index cb172db41b34..155770f18f9c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-usb
> +++ b/Documentation/ABI/testing/sysfs-bus-usb
> @@ -292,6 +292,15 @@ Description:
>  		which is marked with early_stop has failed to initialize, it will ignore
>  		all future connections until this attribute is clear.
>  
> +What:		/sys/bus/usb/devices/.../<hub_interface>/port<X>/state
> +Date:		May 2023

It's June :)

> +Contact:	Roy Luo <royluo@xxxxxxxxxx>
> +Description:
> +		Indicates current state of the USB device attached to the port. Valid
> +		states are: 'not-attached', 'attached', 'powered',
> +		'reconnecting', 'unauthenticated', 'default', 'addressed',
> +		'configured', and 'suspended'.

No mentioning that you can poll on this file?  You went through a lot of
work to add that feature, right?  Or am I mistaking why you added the
sysfs_notify_dirent() calls?  Are they really not needed?  Or are they
needed?

Actually why are they needed?  This is a state change, can't you emit
uevents saying the state changed and if userspace wants to re-read it,
it will?  Or is that too noisy?

Or is any of this needed at all, and you just want to read the file
every once in a while from userspace to see what is going on?

Do you have a pointer to any userspace code that is using this new
interface?

> +
>  What:		/sys/bus/usb/devices/.../power/usb2_lpm_l1_timeout
>  Date:		May 2013
>  Contact:	Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 97a0f8faea6e..a739403a9e45 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2018,6 +2018,19 @@ bool usb_device_is_owned(struct usb_device *udev)
>  	return !!hub->ports[udev->portnum - 1]->port_owner;
>  }
>  
> +static void update_port_device_state(struct usb_device *udev)
> +{
> +	struct usb_hub *hub;
> +	struct usb_port *port_dev;
> +
> +	if (udev->parent) {
> +		hub = usb_hub_to_struct_hub(udev->parent);
> +		port_dev = hub->ports[udev->portnum - 1];
> +		WRITE_ONCE(port_dev->state, udev->state);
> +		sysfs_notify_dirent(port_dev->state_kn);
> +	}
> +}
> +
>  static void recursively_mark_NOTATTACHED(struct usb_device *udev)
>  {
>  	struct usb_hub *hub = usb_hub_to_struct_hub(udev);
> @@ -2030,6 +2043,7 @@ static void recursively_mark_NOTATTACHED(struct usb_device *udev)
>  	if (udev->state == USB_STATE_SUSPENDED)
>  		udev->active_duration -= jiffies;
>  	udev->state = USB_STATE_NOTATTACHED;
> +	update_port_device_state(udev);
>  }
>  
>  /**
> @@ -2086,6 +2100,7 @@ void usb_set_device_state(struct usb_device *udev,
>  				udev->state != USB_STATE_SUSPENDED)
>  			udev->active_duration += jiffies;
>  		udev->state = new_state;
> +		update_port_device_state(udev);
>  	} else
>  		recursively_mark_NOTATTACHED(udev);
>  	spin_unlock_irqrestore(&device_state_lock, flags);
> diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
> index e23833562e4f..37897afd1b64 100644
> --- a/drivers/usb/core/hub.h
> +++ b/drivers/usb/core/hub.h
> @@ -84,6 +84,8 @@ struct usb_hub {
>   * @peer: related usb2 and usb3 ports (share the same connector)
>   * @req: default pm qos request for hubs without port power control
>   * @connect_type: port's connect type
> + * @state: device state of the usb device attached to the port
> + * @state_kn: kernfs_node of the sysfs attribute that accesses @state
>   * @location: opaque representation of platform connector location
>   * @status_lock: synchronize port_event() vs usb_port_{suspend|resume}
>   * @portnum: port index num based one
> @@ -100,6 +102,8 @@ struct usb_port {
>  	struct usb_port *peer;
>  	struct dev_pm_qos_request *req;
>  	enum usb_port_connect_type connect_type;
> +	enum usb_device_state state;
> +	struct kernfs_node *state_kn;
>  	usb_port_location_t location;
>  	struct mutex status_lock;
>  	u32 over_current_count;
> diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
> index 06a8f1f84f6f..2f906e89054e 100644
> --- a/drivers/usb/core/port.c
> +++ b/drivers/usb/core/port.c
> @@ -160,6 +160,16 @@ static ssize_t connect_type_show(struct device *dev,
>  }
>  static DEVICE_ATTR_RO(connect_type);
>  
> +static ssize_t state_show(struct device *dev,
> +			  struct device_attribute *attr, char *buf)
> +{
> +	struct usb_port *port_dev = to_usb_port(dev);
> +	enum usb_device_state state = READ_ONCE(port_dev->state);
> +
> +	return sprintf(buf, "%s\n", usb_state_string(state));

I thought checkpatch would warn you that you should be using
sysfs_emit() here, wonder why it didn't.

thanks,

greg k-h