usb: dwc3: add generic driver to support flattened

To support flattened dwc3 dt model and drop the glue layer, introduce the
`dwc3-generic` driver. This enables direct binding of the DWC3 core driver
and offers an alternative to the existing glue driver `dwc3-of-simple`.

Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Ze Huang <huang.ze@linux.dev>
Link: https://lore.kernel.org/r/20250913-dwc3_generic-v8-2-b50f81f05f95@linux.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250913-dwc3_generic-v8-2-b50f81f05f95@linux.dev

drivers/usb/dwc3/Kconfig

@@ -189,4 +189,15 @@ config USB_DWC3_RTK
 	  or dual-role mode.
 	  Say 'Y' or 'M' if you have such device.
 
+config USB_DWC3_GENERIC_PLAT
+	tristate "DWC3 Generic Platform Driver"
+	depends on OF && COMMON_CLK
+	default USB_DWC3
+	help
+	  Support USB3 functionality in simple SoC integrations.
+	  Currently supports SpacemiT DWC USB3. Platforms using
+	  dwc3-of-simple can easily switch to dwc3-generic by flattening
+	  the dwc3 child node in the device tree.
+	  Say 'Y' or 'M' here if your platform integrates DWC3 in a similar way.
+
 endif

drivers/usb/dwc3/Makefile

@@ -57,3 +57,4 @@ obj-$(CONFIG_USB_DWC3_IMX8MP)		+= dwc3-imx8mp.o
 obj-$(CONFIG_USB_DWC3_XILINX)		+= dwc3-xilinx.o
 obj-$(CONFIG_USB_DWC3_OCTEON)		+= dwc3-octeon.o
 obj-$(CONFIG_USB_DWC3_RTK)		+= dwc3-rtk.o
+obj-$(CONFIG_USB_DWC3_GENERIC_PLAT)	+= dwc3-generic-plat.o

drivers/usb/dwc3/dwc3-generic-plat.c

@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * dwc3-generic-plat.c - DesignWare USB3 generic platform driver
+ *
+ * Copyright (C) 2025 Ze Huang <huang.ze@linux.dev>
+ *
+ * Inspired by dwc3-qcom.c and dwc3-of-simple.c
+ */
+
+#include <linux/clk.h>
+#include <linux/platform_device.h>
+#include <linux/reset.h>
+#include "glue.h"
+
+struct dwc3_generic {
+	struct device		*dev;
+	struct dwc3		dwc;
+	struct clk_bulk_data	*clks;
+	int			num_clocks;
+	struct reset_control	*resets;
+};
+
+#define to_dwc3_generic(d) container_of((d), struct dwc3_generic, dwc)
+
+static void dwc3_generic_reset_control_assert(void *data)
+{
+	reset_control_assert(data);
+}
+
+static int dwc3_generic_probe(struct platform_device *pdev)
+{
+	struct dwc3_probe_data probe_data = {};
+	struct device *dev = &pdev->dev;
+	struct dwc3_generic *dwc3g;
+	struct resource *res;
+	int ret;
+
+	dwc3g = devm_kzalloc(dev, sizeof(*dwc3g), GFP_KERNEL);
+	if (!dwc3g)
+		return -ENOMEM;
+
+	dwc3g->dev = dev;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res) {
+		dev_err(&pdev->dev, "missing memory resource\n");
+		return -ENODEV;
+	}
+
+	dwc3g->resets = devm_reset_control_array_get_optional_exclusive(dev);
+	if (IS_ERR(dwc3g->resets))
+		return dev_err_probe(dev, PTR_ERR(dwc3g->resets), "failed to get resets\n");
+
+	ret = reset_control_assert(dwc3g->resets);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to assert resets\n");
+
+	/* Not strict timing, just for safety */
+	udelay(2);
+
+	ret = reset_control_deassert(dwc3g->resets);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to deassert resets\n");
+
+	ret = devm_add_action_or_reset(dev, dwc3_generic_reset_control_assert, dwc3g->resets);
+	if (ret)
+		return ret;
+
+	ret = devm_clk_bulk_get_all_enabled(dwc3g->dev, &dwc3g->clks);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "failed to get clocks\n");
+
+	dwc3g->num_clocks = ret;
+	dwc3g->dwc.dev = dev;
+	probe_data.dwc = &dwc3g->dwc;
+	probe_data.res = res;
+	probe_data.ignore_clocks_and_resets = true;
+	ret = dwc3_core_probe(&probe_data);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to register DWC3 Core\n");
+
+	return 0;
+}
+
+static void dwc3_generic_remove(struct platform_device *pdev)
+{
+	struct dwc3 *dwc = platform_get_drvdata(pdev);
+	struct dwc3_generic *dwc3g = to_dwc3_generic(dwc);
+
+	dwc3_core_remove(dwc);
+
+	clk_bulk_disable_unprepare(dwc3g->num_clocks, dwc3g->clks);
+}
+
+static int dwc3_generic_suspend(struct device *dev)
+{
+	struct dwc3 *dwc = dev_get_drvdata(dev);
+	struct dwc3_generic *dwc3g = to_dwc3_generic(dwc);
+	int ret;
+
+	ret = dwc3_pm_suspend(dwc);
+	if (ret)
+		return ret;
+
+	clk_bulk_disable_unprepare(dwc3g->num_clocks, dwc3g->clks);
+
+	return 0;
+}
+
+static int dwc3_generic_resume(struct device *dev)
+{
+	struct dwc3 *dwc = dev_get_drvdata(dev);
+	struct dwc3_generic *dwc3g = to_dwc3_generic(dwc);
+	int ret;
+
+	ret = clk_bulk_prepare_enable(dwc3g->num_clocks, dwc3g->clks);
+	if (ret)
+		return ret;
+
+	ret = dwc3_pm_resume(dwc);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int dwc3_generic_runtime_suspend(struct device *dev)
+{
+	return dwc3_runtime_suspend(dev_get_drvdata(dev));
+}
+
+static int dwc3_generic_runtime_resume(struct device *dev)
+{
+	return dwc3_runtime_resume(dev_get_drvdata(dev));
+}
+
+static int dwc3_generic_runtime_idle(struct device *dev)
+{
+	return dwc3_runtime_idle(dev_get_drvdata(dev));
+}
+
+static const struct dev_pm_ops dwc3_generic_dev_pm_ops = {
+	SYSTEM_SLEEP_PM_OPS(dwc3_generic_suspend, dwc3_generic_resume)
+	RUNTIME_PM_OPS(dwc3_generic_runtime_suspend, dwc3_generic_runtime_resume,
+		       dwc3_generic_runtime_idle)
+};
+
+static const struct of_device_id dwc3_generic_of_match[] = {
+	{ .compatible = "spacemit,k1-dwc3", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, dwc3_generic_of_match);
+
+static struct platform_driver dwc3_generic_driver = {
+	.probe		= dwc3_generic_probe,
+	.remove		= dwc3_generic_remove,
+	.driver		= {
+		.name	= "dwc3-generic-plat",
+		.of_match_table = dwc3_generic_of_match,
+		.pm	= pm_ptr(&dwc3_generic_dev_pm_ops),
+	},
+};
+module_platform_driver(dwc3_generic_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("DesignWare USB3 generic platform driver");