On Mon, Oct 14, 2024 at 08:50:29AM +0000, Guan-Yu Lin wrote:
> Sharing a USB controller with another entity via xhci-sideband driver
> creates power management complexities. To prevent the USB controller
> from being inadvertently deactivated while in use by the other entity, a
> usage-count based mechanism is implemented. This allows the system to
> manage power effectively, ensuring the controller remains available
> whenever needed.
>
> Signed-off-by: Guan-Yu Lin <guanyulin@xxxxxxxxxx>
> ---
> drivers/usb/core/driver.c | 10 ++++++++++
> drivers/usb/core/hcd.c | 1 +
> drivers/usb/core/usb.c | 1 +
> drivers/usb/dwc3/core.c | 13 +++++++++++++
> drivers/usb/dwc3/core.h | 8 ++++++++
> drivers/usb/host/xhci-plat.c | 10 ++++++++++
> drivers/usb/host/xhci-plat.h | 7 +++++++
> sound/usb/qcom/qc_audio_offload.c | 3 +++
> 8 files changed, 53 insertions(+)
>
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index e713cf9b3dd2..eb85cbb1a2ff 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1583,6 +1583,11 @@ int usb_suspend(struct device *dev, pm_message_t msg)
> struct usb_device *udev = to_usb_device(dev);
> int r;
>
> + if (msg.event == PM_EVENT_SUSPEND && usb_sideband_check(udev)) {
> + dev_dbg(dev, "device accessed via sideband\n");
> + return 0;
> + }
I'm not so sure about this. By returning early, you prevent the drivers
bound to this device from suspending. But they can't operate properly
when the system is in a low-power mode. Won't that cause problems?
Maybe this really belongs in usb_suspend_device(), and its counterpart
belongs in usb_resume_device().
> +
> unbind_no_pm_drivers_interfaces(udev);
>
> /* From now on we are sure all drivers support suspend/resume
> @@ -1619,6 +1624,11 @@ int usb_resume(struct device *dev, pm_message_t msg)
> struct usb_device *udev = to_usb_device(dev);
> int status;
>
> + if (msg.event == PM_EVENT_RESUME && usb_sideband_check(udev)) {
> + dev_dbg(dev, "device accessed via sideband\n");
> + return 0;
> + }
> +
> /* For all calls, take the device back to full power and
> * tell the PM core in case it was autosuspended previously.
> * Unbind the interfaces that will need rebinding later,
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 1ff7d901fede..9876b3940281 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -2593,6 +2593,7 @@ struct usb_hcd *__usb_create_hcd(const struct hc_driver *driver,
> timer_setup(&hcd->rh_timer, rh_timer_func, 0);
> #ifdef CONFIG_PM
> INIT_WORK(&hcd->wakeup_work, hcd_resume_work);
> + refcount_set(&hcd->sb_usage_count, 0);
Did I miss something? I didn't notice this field in any of the earlier
patches. Was it already created by the prerequisite series? If so, why
didn't that series do this initialization?
> #endif
>
> INIT_WORK(&hcd->died_work, hcd_died_work);
> diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
> index 0b4685aad2d5..d315d066a56b 100644
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -671,6 +671,7 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
> dev->state = USB_STATE_ATTACHED;
> dev->lpm_disable_count = 1;
> atomic_set(&dev->urbnum, 0);
> + refcount_set(&dev->sb_usage_count, 0);
And doesn't this belong in the 3/5 patch, the one that creates the
sb_usage_count field?
Alan Stern
