On Wed, Oct 09, 2024 at 05:42:57AM +0000, Guan-Yu Lin wrote:
> Introduce sb_usage_count and corresponding apis to track sideband usage
> on each usb_device. A sideband refers to the co-processor that accesses
> the usb_device via shared control on the same USB host controller. To
> optimize power usage, it's essential to monitor whether ther sideband is
> actively using the usb_device. This information is vital when
> determining if a usb_device can be safely suspended during system power
> state transitions.
>
> Signed-off-by: Guan-Yu Lin <guanyulin@xxxxxxxxxx>
> ---
> drivers/usb/core/driver.c | 54 +++++++++++++++++++++++++++++++++++++++
> include/linux/usb.h | 13 ++++++++++
> 2 files changed, 67 insertions(+)
>
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index 0c3f12daac79..c1ba5ed15214 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1673,6 +1673,60 @@ void usb_disable_autosuspend(struct usb_device *udev)
> }
> EXPORT_SYMBOL_GPL(usb_disable_autosuspend);
>
> +/**
> + * usb_sideband_get - notify usb driver there's a new active sideband
> + * @udev: the usb_device which has an active sideband
> + *
> + * An active sideband indicates that another entity is currently using the usb
> + * device. Notify the usb device by increasing the sb_usage_count. This allows
> + * usb driver to adjust power management policy based on sideband activities.
> + */
> +void usb_sideband_get(struct usb_device *udev)
> +{
> + struct usb_device *parent = udev;
> +
> + do {
> + atomic_inc(&parent->sb_usage_count);
As this is a reference count, use refcount_t please.
> + parent = parent->parent;
> + } while (parent);
Woah, walking up the device chain? That should not be needed, or if so,
then each device's "usage count" is pointless.
> +}
> +EXPORT_SYMBOL_GPL(usb_sideband_get);
> +
> +/**
> + * usb_sideband_put - notify usb driver there's a sideband deactivated
> + * @udev: the usb_device which has a sideband deactivated
> + *
> + * The inverse operation of usb_sideband_get, which notifies the usb device by
> + * decreasing the sb_usage_count. This allows usb driver to adjust power
> + * management policy based on sideband activities.
> + */
> +void usb_sideband_put(struct usb_device *udev)
> +{
> + struct usb_device *parent = udev;
> +
> + do {
> + atomic_dec(&parent->sb_usage_count);
> + parent = parent->parent;
> + } while (parent);
> +}
> +EXPORT_SYMBOL_GPL(usb_sideband_put);
> +
> +/**
> + * usb_sideband_check - check sideband activities on the host controller
> + * @udev: the usb_device which has a sideband deactivated
> + *
> + * Check if there are any sideband activity on the USB device right now. This
> + * information could be used for power management or other forms or resource
> + * management.
> + *
> + * Returns true on any active sideband existence, false otherwise
> + */
> +bool usb_sideband_check(struct usb_device *udev)
> +{
> + return !!atomic_read(&udev->sb_usage_count);
And what happens if it changes right after you make this call? This
feels racy and broken.
> +}
> +EXPORT_SYMBOL_GPL(usb_sideband_check);
> +
> /**
> * usb_autosuspend_device - delayed autosuspend of a USB device and its interfaces
> * @udev: the usb_device to autosuspend
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index 672d8fc2abdb..5b9fea378960 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -645,6 +645,7 @@ struct usb3_lpm_parameters {
> * parent->hub_delay + wHubDelay + tTPTransmissionDelay (40ns)
> * Will be used as wValue for SetIsochDelay requests.
> * @use_generic_driver: ask driver core to reprobe using the generic driver.
> + * @sb_usage_count: number of active sideband accessing this usb device.
> *
> * Notes:
> * Usbcore drivers should not set usbdev->state directly. Instead use
> @@ -731,6 +732,8 @@ struct usb_device {
>
> u16 hub_delay;
> unsigned use_generic_driver:1;
> +
> + atomic_t sb_usage_count;
Why is this on the device and not the interface that is bound to the
driver that is doing this work?
thanks,
greg k-h
