Re: [RFT PATCH] xhci: dbc: support runtime suspend while DbC is in enabled state

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

Hello Mathias,

On 6/15/2026 2:25 PM, Mathias Nyman wrote:
> Allow xHC to runtime suspend if DbC is in 'enabled' state for over
> 15 seconds without a connect.
> 
> Idea is that every time we go to 'enabled' state we make sure DbC runtime
> pm usage is '1' and save a timestamp. if the event loop still finds DbC in
> enabled state 15 seconds later then it decrease DbC runtime pm usage by
> calling pm_runtime_put().
> Enabled state is reached either when DbC is enabled by userspace or a
> connected/configured DbC is disconnected.
> 
> When a connect is detected we make sure DbC usage count is 1.
> 
> If DbC has been in 'enabled' state for 15 seconds and DbC usage is
> decreased to 0 by pm_runtime_put, then the whole xHC controller may
> runtime suspends to PCI D3 state if no other devices are using it
> 
> DbC sysfs file will show 'suspended' when xHC is suspended and will wake up
> and enable DbC at cable connect, or when user writes 'enable' to the file.
> 

The patch helps. Thank you!
Anytime time line on getting it merged?

==
Chaitanya

> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> ---
>   .../testing/sysfs-bus-pci-drivers-xhci_hcd    |  2 +-
>   drivers/usb/host/xhci-dbgcap.c                | 60 ++++++++++++++++++-
>   drivers/usb/host/xhci-dbgcap.h                |  3 +
>   3 files changed, 62 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
> index 98a8376a83d2..991765d84201 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
> +++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
> @@ -22,7 +22,7 @@ Description:
>   
>   		Reading this attribute gives the state of the DbC. It
>   		can be one of the following states: disabled, enabled,
> -		initialized, connected or configured.
> +		initialized, connected, configured or suspended.
>   
>   What:		/sys/bus/pci/drivers/xhci_hcd/.../dbc_idVendor
>   Date:		March 2023
> diff --git a/drivers/usb/host/xhci-dbgcap.c b/drivers/usb/host/xhci-dbgcap.c
> index 8ff8ac300927..f228c46293ca 100644
> --- a/drivers/usb/host/xhci-dbgcap.c
> +++ b/drivers/usb/host/xhci-dbgcap.c
> @@ -647,6 +647,31 @@ static int xhci_dbc_enable_dce(struct xhci_dbc *dbc, bool enable)
>   
>   static void xhci_dbc_set_state(struct xhci_dbc *dbc, enum dbc_state new_state)
>   {
> +	if (dbc->state == new_state)
> +		return;
> +
> +	switch (new_state) {
> +	case DS_ENABLED:
> +		/*
> +		 * DbC pm usage is 1 here, both when moved from disconnect or
> +		 * configured states, or when setting initial DbC enable state.
> +		 * Just enable pending put
> +		 */
> +		dev_dbg(dbc->dev, "DbC set pending_rpm_put = 1\n");
> +		dbc->pending_rpm_put = 1;
> +		break;
> +	case DS_CONNECTED:
> +		if (dbc->pending_rpm_put)
> +			/* DbC pm usage still 1, just remove pending put */
> +			dbc->pending_rpm_put = 0;
> +		else
> +			/* DbC pm usage was put to 0, call get */
> +			pm_runtime_get(dbc->dev);
> +		break;
> +	default:
> +		break;
> +	}
> +
>   	dbc->state_timestamp = jiffies;
>   	dbc->state = new_state;
>   }
> @@ -682,7 +707,7 @@ static int xhci_dbc_start(struct xhci_dbc *dbc)
>   
>   	WARN_ON(!dbc);
>   
> -	pm_runtime_get_sync(dbc->dev); /* note this was self.controller */
> +	pm_runtime_get(dbc->dev);
>   
>   	spin_lock_irqsave(&dbc->lock, flags);
>   	ret = xhci_do_dbc_start(dbc);
> @@ -707,6 +732,7 @@ static int xhci_dbc_start(struct xhci_dbc *dbc)
>   static void xhci_dbc_stop(struct xhci_dbc *dbc)
>   {
>   	unsigned long		flags;
> +	bool			need_rpm_put = false;
>   
>   	WARN_ON(!dbc);
>   
> @@ -732,12 +758,20 @@ static void xhci_dbc_stop(struct xhci_dbc *dbc)
>   
>   	spin_lock_irqsave(&dbc->lock, flags);
>   	writel(0, &dbc->regs->control);
> +
> +	if (dbc->state == DS_CONNECTED || dbc->state == DS_CONFIGURED ||
> +	    dbc->pending_rpm_put)
> +		need_rpm_put = true;
> +
> +	dbc->pending_rpm_put = 0;
> +
>   	xhci_dbc_set_state(dbc, DS_DISABLED);
>   	spin_unlock_irqrestore(&dbc->lock, flags);
>   
>   	xhci_dbc_mem_cleanup(dbc);
>   
> -	pm_runtime_put(dbc->dev); /* note, was self.controller */
> +	if (need_rpm_put)
> +		pm_runtime_put(dbc->dev);
>   }
>   
>   static void
> @@ -911,6 +945,12 @@ static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
>   			dev_info(dbc->dev, "DbC connected\n");
>   		} else if (!(ctrl & DBC_CTRL_DBC_ENABLE)) {
>   			dev_err(dbc->dev, "unexpected DbC disable, xHC reset?\n");
> +		} else if (dbc->pending_rpm_put &&
> +			   time_is_before_jiffies(dbc->state_timestamp +
> +				msecs_to_jiffies(DBC_AUTOSUSPEND_DELAY))) {
> +			dbc->pending_rpm_put = 0;
> +			dev_dbg(dbc->dev, "DbC Enabled state for 15 seconds, allow rpm suspend\n");
> +			pm_runtime_put(dbc->dev);
>   		}
>   
>   		return EVT_DONE;
> @@ -1099,6 +1139,9 @@ static ssize_t dbc_show(struct device *dev,
>   	if (dbc->state >= ARRAY_SIZE(dbc_state_strings))
>   		return sysfs_emit(buf, "unknown\n");
>   
> +	if (dbc->resume_required)
> +		return sysfs_emit(buf, "suspended\n");
> +
>   	return sysfs_emit(buf, "%s\n", dbc_state_strings[dbc->state]);
>   }
>   
> @@ -1113,12 +1156,25 @@ static ssize_t dbc_store(struct device *dev,
>   	dbc = xhci->dbc;
>   
>   	if (sysfs_streq(buf, "enable")) {
> +		pm_runtime_get_sync(dbc->dev);
> +
>   		mutex_lock(&dbc->enable_mutex);
> +		/*
> +		 * DbC may already be enabled here if xhci was suspended with
> +		 * dbc->resume_required set, and resumed by pm_runtime_get_sync()
> +		 * above. In this case we end up calling xhci_dbc_start() twice,
> +		 * second time returns an error but is harmless
> +		 */
>   		xhci_dbc_start(dbc);
> +
>   		mutex_unlock(&dbc->enable_mutex);
> +		pm_runtime_put(dbc->dev);
>   	} else if (sysfs_streq(buf, "disable")) {
>   		mutex_lock(&dbc->enable_mutex);
> +
> +		dbc->resume_required = 0;
>   		xhci_dbc_stop(dbc);
> +
>   		mutex_unlock(&dbc->enable_mutex);
>   	} else {
>   		return -EINVAL;
> diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
> index df7aca8bfe99..5b18efb2c1ea 100644
> --- a/drivers/usb/host/xhci-dbgcap.h
> +++ b/drivers/usb/host/xhci-dbgcap.h
> @@ -114,6 +114,8 @@ struct dbc_ep {
>   #define DBC_POLL_INTERVAL_MAX		5000	/* milliseconds */
>   #define DBC_XFER_INACTIVITY_TIMEOUT	10	/* milliseconds */
>   #define DBC_ENUMERATION_TIMEOUT		2000	/* milliseconds */
> +#define DBC_AUTOSUSPEND_DELAY		15000	/* milliseconds */
> +
>   /*
>    * Private structure for DbC hardware state:
>    */
> @@ -166,6 +168,7 @@ struct xhci_dbc {
>   	unsigned long			xfer_timestamp;
>   	unsigned long			state_timestamp;
>   	unsigned			resume_required:1;
> +	unsigned			pending_rpm_put:1;
>   	struct dbc_ep			eps[2];
>   
>   	const struct dbc_driver		*driver;