[PATCH v6 4/5] 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 false.

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.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/usb/host/xhci.c | 3 ++-
 drivers/usb/host/xhci.h | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 5ebde8cae4fc44cdb997b0f61314e309bda56c0d..ae2c8daa206a87da24d58a62b0a0485ebf68cdd6 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -1017,7 +1017,8 @@ 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->quirks & XHCI_RESET_ON_RESUME ||
+	    xhci->broken_suspend || xhci->lost_power)
 		reinit_xhc = true;
 
 	if (!reinit_xhc) {
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 4914f0a10cff42dbc1448dcf7908534d582c848e..32526df75925989d40cbe7d59a187c945f498a30 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1645,6 +1645,12 @@ 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;

-- 
2.47.1