[PATCH v5 09/12] xhci: introduce xhci->lost_power flag

["Théo Lebrun" <theo.lebrun@bootlin.com>]

The XHCI_RESET_ON_RESUME quirk allows wrappers to signal that they
expect a reset after resume. It is also used by some to enforce a XHCI
reset on resume (see needs-reset-on-resume DT prop).

Some wrappers are unsure beforehands if they will reset. Add a mechanism
to signal *at resume* if power has been lost. Parent devices can set
this flag, that defaults to the XHCI_RESET_ON_RESUME value.

The XHCI_RESET_ON_RESUME quirk still triggers a runtime_pm_get() on the
controller. This is required as we do not know if a suspend will
trigger a reset, so the best guess is to avoid runtime PM.

Reset the xhci->lost_power value each time in xhci_resume(), making it
safe for devices to only set lost_power on some resumes.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/usb/host/xhci.c | 8 +++++++-
 drivers/usb/host/xhci.h | 6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 0a8cf6c17f82..2c9b32d339f9 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -1029,9 +1029,12 @@ int xhci_resume(struct xhci_hcd *xhci, pm_message_t msg)
 
 	spin_lock_irq(&xhci->lock);
 
-	if (hibernated || xhci->quirks & XHCI_RESET_ON_RESUME || xhci->broken_suspend)
+	if (hibernated || xhci->lost_power || xhci->broken_suspend)
 		reinit_xhc = true;
 
+	/* Reset to default value, parent devices might correct it at next resume. */
+	xhci->lost_power = !!(xhci->quirks & XHCI_RESET_ON_RESUME);
+
 	if (!reinit_xhc) {
 		/*
 		 * Some controllers might lose power during suspend, so wait
@@ -5228,6 +5231,9 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks)
 	if (get_quirks)
 		get_quirks(dev, xhci);
 
+	/* Default value, that can be corrected at resume. */
+	xhci->lost_power = !!(xhci->quirks & XHCI_RESET_ON_RESUME);
+
 	/* In xhci controllers which follow xhci 1.0 spec gives a spurious
 	 * success event after a short transfer. This quirk will ignore such
 	 * spurious event.
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index ebd0afd59a60..ec7c6061363f 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1640,6 +1640,12 @@ struct xhci_hcd {
 	unsigned		broken_suspend:1;
 	/* Indicates that omitting hcd is supported if root hub has no ports */
 	unsigned		allow_single_roothub:1;
+	/*
+	 * Signal from upper stacks that we lost power during system-wide
+	 * suspend. Its default value is based on XHCI_RESET_ON_RESUME, meaning
+	 * it is safe for wrappers to not modify lost_power at resume.
+	 */
+	unsigned                lost_power:1;
 	/* cached extended protocol port capabilities */
 	struct xhci_port_cap	*port_caps;
 	unsigned int		num_port_caps;

-- 
2.45.2