linux-kernel - [PATCH v2] usb: dwc3: core: Avoid redundant system suspend/resume callbacks

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Message-ID: <20250312223434.3071598-1-royluo@google.com>
Date: Wed, 12 Mar 2025 22:34:34 +0000
From: Roy Luo <royluo@...gle.com>
To: royluo@...gle.com, Thinh.Nguyen@...opsys.com, gregkh@...uxfoundation.org, 
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] usb: dwc3: core: Avoid redundant system suspend/resume callbacks

dwc3 device suspend/resume callbacks were being triggered during system
suspend and resume even if the device was already runtime-suspended.
This is redundant for device mode because the suspend and resume routines
are essentially identical for system PM and runtime PM.

To prevent these unnecessary callbacks, indicate to the PM core that it
can safely leave the device in runtime suspend if it's already
runtime-suspended in device mode by returning a positive value in
prepare() callback. This optimization only applies to devices without
pinctrl, as pinctrl has distinct logic tied to system suspend/resume.

Signed-off-by: Roy Luo <royluo@...gle.com>
---
Changes in v2:
- leave the pinctrl logic untouched, apply the optimization only when
  pinctrl isn't being used.
---
 drivers/usb/dwc3/core.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 66a08b527165..02cdd0727a5e 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -26,6 +26,7 @@
 #include <linux/of_graph.h>
 #include <linux/acpi.h>
 #include <linux/pinctrl/consumer.h>
+#include <linux/pinctrl/devinfo.h>
 #include <linux/reset.h>
 #include <linux/bitfield.h>
 
@@ -2658,14 +2659,31 @@ static void dwc3_complete(struct device *dev)
 		dwc3_writel(dwc->regs, DWC3_GUCTL3, reg);
 	}
 }
+
+static int dwc3_prepare(struct device *dev)
+{
+	struct dwc3	*dwc = dev_get_drvdata(dev);
+
+	/*
+	 * Indicate to the PM core that it may safely leave the device in
+	 * runtime suspend if runtime-suspended already in device mode.
+	 */
+	if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_DEVICE &&
+	    pm_runtime_suspended(dev) &&
+	    !dev_pinctrl(dev))
+		return 1;
+
+	return 0;
+}
 #else
 #define dwc3_complete NULL
+#define dwc3_prepare NULL
 #endif /* CONFIG_PM_SLEEP */
 
 static const struct dev_pm_ops dwc3_dev_pm_ops = {
 	SET_SYSTEM_SLEEP_PM_OPS(dwc3_suspend, dwc3_resume)
 	.complete = dwc3_complete,
-
+	.prepare = dwc3_prepare,
 	/*
 	 * Runtime suspend halts the controller on disconnection. It relies on
 	 * platforms with custom connection notification to start the controller

base-commit: 0fed89a961ea851945d23cc35beb59d6e56c0964
-- 
2.49.0.rc1.451.g8f38331e32-goog