概念

在OTG中，初始主机设备称为A设备，外设称为B设备。可用电缆的连接方式来决定初始角色。两用设备使用新型Mini-AB插座，从而使Mini-A插头、Mini-B插头和Mini-AB插座增添了第5个引脚（ID），以用于识别不同的电缆端点。Mini-A插头中的ID引脚接地，Mini-B插头中的ID引脚浮空。当OTG设备检测到接地的ID引脚时，表示默认的是A设备（主机），而检测到ID引脚浮空的设备则认为是B设备（外设）。系统一旦连接后，OTG的角色还可以更换，以采用新的HNP协议。而SRP允许B设备请求A设备打开VBUS电源并启动一次对话。

设备树

我们直接看支持otg的dwc3是怎么处理otg的，从设备开始看驱动，usb3_0的这个节点一般就是厂商自己定义的，主要包括中断，一般用于vbus检测，usb的插拔情况；dwc3_0这个子节点就是通用的dwc3核心，主要包括中断，一般用于id脚的检测，来判断当前是设备还是主机；如果dr_mode设置了模式，就会用固定的模式去初始化控制器

usb3phy: usb3phy@c0030000 {
        compatible = "usb3-phy";
        reg = <0xc0030000 0x1000>;
        clocks = <&soc_clocks CLK_USB>;
        clock-names = "usb_clk";
        status = "disabled";
};
usb3_0: usb3-0 {
        compatible = "arch,dwc3";
        #address-cells = <1>;
        #size-cells = <1>;
        ranges;
        interrupts = <53>;
        clocks = <&soc_clocks CLK_USB>;
        clock-names = "usb_clk";
        status = "disabled";
        usb_dwc3_0: dwc31@c0000000 {
                compatible = "snps,dwc3";
                reg = <0xc0000000 0x11000>;
                interrupts = <44>;
                usb-phy = <&usb3phy>;
                maximum-speed = "super-speed";
                dr_mode = "peripheral";
                phy_type = "utmi";
                lpm-qos = <PM_QOS_CPUIDLE_BLOCK_AXI>;
                snps,dis_u3_susphy_quirk;
                /* allow-suspend; */
                status = "okay";
        };
};

驱动框架

设备树跟驱动match后，会执行dwc3_probe；主要是一些初始化操作，如果设置了dr_mode为peripheral，就调用dwc_gadget_init去初始化设备控制器；dr_mode为host，就调用dwc3_host_init去初始化为主机控制器；如果dr_mode为otg，就根据id的情况去初始化为主机或设备

dwc3_probe
    dwc3_get_dr_mode
    dwc3_core_init
    dwc3_debugfs_init
    dwc3_core_init_mode//根据模式进入一种
        dwc3_gadget_init
            dwc->gadget.ops	= &dwc3_gadget_ops;//初始化设备控制器操作函数
            dwc3_gadget_init_endpoints(dwc, dwc->num_eps);
                dep->endpoint.ops = &dwc3_gadget_ep_ops;
            usb_add_gadget_udc(dwc->dev, &dwc->gadget);//注册设备控制器
        dwc3_host_init
            xhci = platform_device_alloc("xhci-hcd", PLATFORM_DEVID_AUTO);
            platform_device_add(xhci)//初始化xhci平台设备；用于匹配到usb_xhci_driver-----其probe来初始化主机控制器，填充操作函数xhci_hc_driver，并注册主机控制器
        dwc3_drd_init
            request_threaded_irq(dwc->otg_irq, dwc3_otg_irq,dwc3_otg_thread_irq,IRQF_SHARED, "dwc3-otg", dwc);
                dwc3_set_mode
                    __dwc3_set_mode
                        dwc3_otg_update//根据模式进入一种
                            dwc3_host_init
                            dwc3_gadget_init

主机控制器的初始化

上面的代码分析到：dwc3_host_init会通过 platform_device_add(xhci)//初始化xhci平台设备；用于匹配到usb_xhci_driver-----其probe来初始化主机控制器，填充操作函数xhci_hc_driver，并注册主机控制器

drivers/usb/host/xhci-plat.c中的usb_xhci_driver通过name(xhci-hcd)匹配上;xhci_init_driver将通用的xhci_hc_driver，赋值给xhci_plat_hc_driver；过程跟ehci_init_driver一致

static int xhci_plat_probe(struct platform_device *pdev)
{
	const struct xhci_plat_priv *priv_match;
	const struct hc_driver	*driver;
	struct device		*sysdev, *tmpdev;
	struct xhci_hcd		*xhci;
	struct resource         *res;
	struct usb_hcd		*hcd;
	int			ret;
	int			irq;
	struct xhci_plat_priv	*priv = NULL;


	if (usb_disabled())
		return -ENODEV;

	driver = &xhci_plat_hc_driver;

	irq = platform_get_irq(pdev, 0);
	if (irq < 0)
		return irq;

	/*
	 * sysdev must point to a device that is known to the system firmware
	 * or PCI hardware. We handle these three cases here:
	 * 1. xhci_plat comes from firmware
	 * 2. xhci_plat is child of a device from firmware (dwc3-plat)
	 * 3. xhci_plat is grandchild of a pci device (dwc3-pci)
	 */
	for (sysdev = &pdev->dev; sysdev; sysdev = sysdev->parent) {
		if (is_of_node(sysdev->fwnode) ||
			is_acpi_device_node(sysdev->fwnode))
			break;
#ifdef CONFIG_PCI
		else if (sysdev->bus == &pci_bus_type)
			break;
#endif
	}

	if (!sysdev)
		sysdev = &pdev->dev;

	/* Try to set 64-bit DMA first */
	if (WARN_ON(!sysdev->dma_mask))
		/* Platform did not initialize dma_mask */
		ret = dma_coerce_mask_and_coherent(sysdev,
						   DMA_BIT_MASK(64));
	else
		ret = dma_set_mask_and_coherent(sysdev, DMA_BIT_MASK(64));

	/* If seting 64-bit DMA mask fails, fall back to 32-bit DMA mask */
	if (ret) {
		ret = dma_set_mask_and_coherent(sysdev, DMA_BIT_MASK(32));
		if (ret)
			return ret;
	}

	pm_runtime_set_active(&pdev->dev);
	pm_runtime_enable(&pdev->dev);
	pm_runtime_get_noresume(&pdev->dev);

	hcd = __usb_create_hcd(driver, sysdev, &pdev->dev,
			       dev_name(&pdev->dev), NULL);
	if (!hcd) {
		ret = -ENOMEM;
		goto disable_runtime;
	}

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	hcd->regs = devm_ioremap_resource(&pdev->dev, res);
	if (IS_ERR(hcd->regs)) {
		ret = PTR_ERR(hcd->regs);
		goto put_hcd;
	}

	hcd->rsrc_start = res->start;
	hcd->rsrc_len = resource_size(res);

	xhci = hcd_to_xhci(hcd);

	/*
	 * Not all platforms have clks so it is not an error if the
	 * clock do not exist.
	 */
	xhci->reg_clk = devm_clk_get_optional(&pdev->dev, "reg");
	if (IS_ERR(xhci->reg_clk)) {
		ret = PTR_ERR(xhci->reg_clk);
		goto put_hcd;
	}

	ret = clk_prepare_enable(xhci->reg_clk);
	if (ret)
		goto put_hcd;

	xhci->clk = devm_clk_get_optional(&pdev->dev, NULL);
	if (IS_ERR(xhci->clk)) {
		ret = PTR_ERR(xhci->clk);
		goto disable_reg_clk;
	}

	ret = clk_prepare_enable(xhci->clk);
	if (ret)
		goto disable_reg_clk;

	priv_match = of_device_get_match_data(&pdev->dev);
	if (priv_match) {
		priv = hcd_to_xhci_priv(hcd);
		/* Just copy data for now */
		if (priv_match)
			*priv = *priv_match;
	}

	device_wakeup_enable(hcd->self.controller);

	xhci->main_hcd = hcd;
	xhci->shared_hcd = __usb_create_hcd(driver, sysdev, &pdev->dev,
			dev_name(&pdev->dev), hcd);
	if (!xhci->shared_hcd) {
		ret = -ENOMEM;
		goto disable_clk;
	}

	/* imod_interval is the interrupt moderation value in nanoseconds. */
	xhci->imod_interval = 40000;

	/* Iterate over all parent nodes for finding quirks */
	for (tmpdev = &pdev->dev; tmpdev; tmpdev = tmpdev->parent) {

		if (device_property_read_bool(tmpdev, "usb2-lpm-disable"))
			xhci->quirks |= XHCI_HW_LPM_DISABLE;

		if (device_property_read_bool(tmpdev, "usb3-lpm-capable"))
			xhci->quirks |= XHCI_LPM_SUPPORT;

		if (device_property_read_bool(tmpdev, "quirk-broken-port-ped"))
			xhci->quirks |= XHCI_BROKEN_PORT_PED;

		device_property_read_u32(tmpdev, "imod-interval-ns",
					 &xhci->imod_interval);
	}

	hcd->usb_phy = devm_usb_get_phy_by_phandle(sysdev, "usb-phy", 0);
	if (IS_ERR(hcd->usb_phy)) {
		ret = PTR_ERR(hcd->usb_phy);
		if (ret == -EPROBE_DEFER)
			goto put_usb3_hcd;
		hcd->usb_phy = NULL;
	} else {
		ret = usb_phy_init(hcd->usb_phy);
		if (ret)
			goto put_usb3_hcd;
	}

	hcd->tpl_support = of_usb_host_tpl_support(sysdev->of_node);
	xhci->shared_hcd->tpl_support = hcd->tpl_support;

	if (priv) {
		ret = xhci_priv_plat_setup(hcd);
		if (ret)
			goto disable_usb_phy;
	}

	if ((xhci->quirks & XHCI_SKIP_PHY_INIT) || (priv && (priv->quirks & XHCI_SKIP_PHY_INIT)))
		hcd->skip_phy_initialization = 1;

	ret = usb_add_hcd(hcd, irq, IRQF_SHARED);
	if (ret)
		goto disable_usb_phy;

	if (HCC_MAX_PSA(xhci->hcc_params) >= 4)
		xhci->shared_hcd->can_do_streams = 1;

	ret = usb_add_hcd(xhci->shared_hcd, irq, IRQF_SHARED);
	if (ret)
		goto dealloc_usb2_hcd;

	device_enable_async_suspend(&pdev->dev);
	pm_runtime_put_noidle(&pdev->dev);

	/*
	 * Prevent runtime pm from being on as default, users should enable
	 * runtime pm using power/control in sysfs.
	 */
	pm_runtime_forbid(&pdev->dev);

	return 0;
....
}
static struct platform_driver usb_xhci_driver = {
	.probe	= xhci_plat_probe,
	.remove	= xhci_plat_remove,
	.shutdown = usb_hcd_platform_shutdown,
	.driver	= {
		.name = "xhci-hcd",
		.pm = &xhci_plat_pm_ops,
		.of_match_table = of_match_ptr(usb_xhci_of_match),
		.acpi_match_table = ACPI_PTR(usb_xhci_acpi_match),
	},
};
MODULE_ALIAS("platform:xhci-hcd");

static int __init xhci_plat_init(void)
{
	xhci_init_driver(&xhci_plat_hc_driver, &xhci_plat_overrides);
	return platform_driver_register(&usb_xhci_driver);
}
module_init(xhci_plat_init);

static void __exit xhci_plat_exit(void)
{
	platform_driver_unregister(&usb_xhci_driver);
}
module_exit(xhci_plat_exit);

dwc3_core_init_mode

dwc3_core_init_mode根据设备树获得的模式，初始化控制器为对应模式，初始化控制器的操作函数：主机有主机的操作函数；设备有设备的操作函数

static int dwc3_core_init_mode(struct dwc3 *dwc)
{
        struct device *dev = dwc->dev;
        int ret;

        switch (dwc->dr_mode) {
        case USB_DR_MODE_PERIPHERAL:
                dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_DEVICE);

                if (dwc->usb2_phy)
                        otg_set_vbus(dwc->usb2_phy->otg, false);
                phy_set_mode(dwc->usb2_generic_phy, PHY_MODE_USB_DEVICE);
                phy_set_mode(dwc->usb3_generic_phy, PHY_MODE_USB_DEVICE);

                ret = dwc3_gadget_init(dwc);
                if (ret) {
                        if (ret != -EPROBE_DEFER)
                                dev_err(dev, "failed to initialize gadget\n");
                        return ret;
                }
                break;
        case USB_DR_MODE_HOST:
                dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_HOST);

                if (dwc->usb2_phy)
                        otg_set_vbus(dwc->usb2_phy->otg, true);
                phy_set_mode(dwc->usb2_generic_phy, PHY_MODE_USB_HOST);
                phy_set_mode(dwc->usb3_generic_phy, PHY_MODE_USB_HOST);

                ret = dwc3_host_init(dwc);
                if (ret) {
                        if (ret != -EPROBE_DEFER)
                                dev_err(dev, "failed to initialize host\n");
                        return ret;
                }
                break;
        case USB_DR_MODE_OTG:
                INIT_WORK(&dwc->drd_work, __dwc3_set_mode);
                ret = dwc3_drd_init(dwc);
                if (ret) {
                        if (ret != -EPROBE_DEFER)
                                dev_err(dev, "failed to initialize dual-role\n");
                        return ret;
                }
                break;
        default:
                dev_err(dev, "Unsupported mode of operation %d\n", dwc->dr_mode);
                return -EINVAL;
        }

        return 0;
}

OTG模式

注册中断

一般是通过id脚注册中断：use OTG block to get ID event

int dwc3_drd_init(struct dwc3 *dwc)
{
        int ret, irq;

        dwc->edev = dwc3_get_extcon(dwc);
        if (IS_ERR(dwc->edev))
                return PTR_ERR(dwc->edev);

        if (ROLE_SWITCH &&
            device_property_read_bool(dwc->dev, "usb-role-switch")) {
                ret = dwc3_setup_role_switch(dwc);
                if (ret < 0)
                        return ret;
        } else if (dwc->edev) {
                dwc->edev_nb.notifier_call = dwc3_drd_notifier;
                ret = extcon_register_notifier(dwc->edev, EXTCON_USB_HOST,
                                               &dwc->edev_nb);
                if (ret < 0) {
                        dev_err(dwc->dev, "couldn't register cable notifier\n");
                        return ret;
                }

                dwc3_drd_update(dwc);
        } else {
                dwc3_set_prtcap(dwc, DWC3_GCTL_PRTCAP_OTG);
                dwc->current_dr_role = DWC3_GCTL_PRTCAP_OTG;

                /* use OTG block to get ID event */
                irq = dwc3_otg_get_irq(dwc);
                if (irq < 0)
                        return irq;

                dwc->otg_irq = irq;

                /* disable all OTG IRQs */
                dwc3_otg_disable_events(dwc, DWC3_OTG_ALL_EVENTS);
                /* clear all events */
                dwc3_otg_clear_events(dwc);

                ret = request_threaded_irq(dwc->otg_irq, dwc3_otg_irq,
                                           dwc3_otg_thread_irq,
                                           IRQF_SHARED, "dwc3-otg", dwc);
                if (ret) {
                        dev_err(dwc->dev, "failed to request irq #%d --> %d\n",
                                dwc->otg_irq, ret);
                        ret = -ENODEV;
                        return ret;
                }

                dwc3_otg_init(dwc);
                dwc3_set_mode(dwc, DWC3_GCTL_PRTCAP_OTG);
        }

        return 0;
}

中断处理

根据id脚的状态,判断是做主机还是设备

static irqreturn_t dwc3_otg_irq(int irq, void *_dwc)
{
        u32 reg;
        struct dwc3 *dwc = _dwc;
        irqreturn_t ret = IRQ_NONE;

        reg = dwc3_readl(dwc->regs, DWC3_OEVT);
        if (reg) {
                /* ignore non OTG events, we can't disable them in OEVTEN */
                if (!(reg & DWC3_OTG_ALL_EVENTS)) {
                        dwc3_writel(dwc->regs, DWC3_OEVT, reg);
                        return IRQ_NONE;
                }

                if (dwc->current_otg_role == DWC3_OTG_ROLE_HOST &&
                    !(reg & DWC3_OEVT_DEVICEMODE))
                        dwc->otg_restart_host = 1;
                dwc3_writel(dwc->regs, DWC3_OEVT, reg);
                ret = IRQ_WAKE_THREAD;
        }

        return ret;
}

可以看作中断下半部，来通过dwc3_set_mode将控制器初始化为主机或者设备

static irqreturn_t dwc3_otg_thread_irq(int irq, void *_dwc)
{
        struct dwc3 *dwc = _dwc;

        spin_lock(&dwc->lock);
        if (dwc->otg_restart_host) {
                dwc3_otg_host_init(dwc);
                dwc->otg_restart_host = 0;
        }

        spin_unlock(&dwc->lock);

        dwc3_set_mode(dwc, DWC3_GCTL_PRTCAP_OTG);

        return IRQ_HANDLED;
}


void dwc3_set_mode(struct dwc3 *dwc, u32 mode)
{
        unsigned long flags;

        spin_lock_irqsave(&dwc->lock, flags);
        dwc->desired_dr_role = mode;
        spin_unlock_irqrestore(&dwc->lock, flags);

        queue_work(system_freezable_wq, &dwc->drd_work);
}

设置模式

模式设置的是设备或者主机，就直接调用dwc3_gadget_init或者dwc3_host_init初始化控制器；如果是otg模式，就要根据dwc3_otg_update去判断id脚的情况来更新为设备或者主机

static void __dwc3_set_mode(struct work_struct *work)
{
        struct dwc3 *dwc = work_to_dwc(work);
        unsigned long flags;
        int ret;
        u32 reg;

        if (dwc->dr_mode != USB_DR_MODE_OTG)
                return;

        if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_OTG)
                dwc3_otg_update(dwc, 0);

        if (!dwc->desired_dr_role)
                return;

        if (dwc->desired_dr_role == dwc->current_dr_role)
                return;

        if (dwc->desired_dr_role == DWC3_GCTL_PRTCAP_OTG && dwc->edev)
                return;

        switch (dwc->current_dr_role) {
        case DWC3_GCTL_PRTCAP_HOST:
                dwc3_host_exit(dwc);
                break;
        case DWC3_GCTL_PRTCAP_DEVICE:
                dwc3_gadget_exit(dwc);
                dwc3_event_buffers_cleanup(dwc);
                break;
        case DWC3_GCTL_PRTCAP_OTG:
                dwc3_otg_exit(dwc);
                spin_lock_irqsave(&dwc->lock, flags);
                dwc->desired_otg_role = DWC3_OTG_ROLE_IDLE;
                spin_unlock_irqrestore(&dwc->lock, flags);
                dwc3_otg_update(dwc, 1);
                break;
        default:
                break;
        }

        spin_lock_irqsave(&dwc->lock, flags);

        dwc3_set_prtcap(dwc, dwc->desired_dr_role);

        spin_unlock_irqrestore(&dwc->lock, flags);

        switch (dwc->desired_dr_role) {
        case DWC3_GCTL_PRTCAP_HOST:
                ret = dwc3_host_init(dwc);
                if (ret) {
                        dev_err(dwc->dev, "failed to initialize host\n");
                } else {
                        if (dwc->usb2_phy)
                                otg_set_vbus(dwc->usb2_phy->otg, true);
                        phy_set_mode(dwc->usb2_generic_phy, PHY_MODE_USB_HOST);
                        phy_set_mode(dwc->usb3_generic_phy, PHY_MODE_USB_HOST);
                        if (dwc->dis_split_quirk) {
                                reg = dwc3_readl(dwc->regs, DWC3_GUCTL3);
                                reg |= DWC3_GUCTL3_SPLITDISABLE;
                                dwc3_writel(dwc->regs, DWC3_GUCTL3, reg);
                                dwc3_save_controller_regs(DWC3_GUCTL3, reg);
                        }
                }
                break;
        case DWC3_GCTL_PRTCAP_DEVICE:
                dwc3_event_buffers_setup(dwc);

                if (dwc->usb2_phy)
                        otg_set_vbus(dwc->usb2_phy->otg, false);
                phy_set_mode(dwc->usb2_generic_phy, PHY_MODE_USB_DEVICE);
                phy_set_mode(dwc->usb3_generic_phy, PHY_MODE_USB_DEVICE);

                ret = dwc3_gadget_init(dwc);
                if (ret)
                        dev_err(dwc->dev, "failed to initialize peripheral\n");
                break;
        case DWC3_GCTL_PRTCAP_OTG:
                dwc3_otg_init(dwc);
                dwc3_otg_update(dwc, 0);
                break;
        default:
                break;
        }
}

更新模式

ignore_idstatus为0，就回去读id相关寄存器，获取id脚的状态desired_otg_role；为高就是DWC3_OTG_ROLE_DEVICE，为低就是DWC3_OTG_ROLE_HOST；跟current_otg_role一样就返回，不一样就关掉当前的控制器，初始化为desired_otg_role的控制器模式

void dwc3_otg_update(struct dwc3 *dwc, bool ignore_idstatus)
{
	int ret;
	u32 reg;
	int id;
	unsigned long flags;

	if (dwc->dr_mode != USB_DR_MODE_OTG)
		return;

	/* don't do anything if debug user changed role to not OTG */
	if (dwc->current_dr_role != DWC3_GCTL_PRTCAP_OTG)
		return;

	if (!ignore_idstatus) {
		reg = dwc3_readl(dwc->regs, DWC3_OSTS);
		id = !!(reg & DWC3_OSTS_CONIDSTS);

		dwc->desired_otg_role = id ? DWC3_OTG_ROLE_DEVICE :
					DWC3_OTG_ROLE_HOST;
	}

	if (dwc->desired_otg_role == dwc->current_otg_role)
		return;

	switch (dwc->current_otg_role) {
	case DWC3_OTG_ROLE_HOST:
		dwc3_host_exit(dwc);
		spin_lock_irqsave(&dwc->lock, flags);
		dwc3_otg_host_exit(dwc);
		spin_unlock_irqrestore(&dwc->lock, flags);
		break;
	case DWC3_OTG_ROLE_DEVICE:
		dwc3_gadget_exit(dwc);
		spin_lock_irqsave(&dwc->lock, flags);
		dwc3_event_buffers_cleanup(dwc);
		dwc3_otg_device_exit(dwc);
		spin_unlock_irqrestore(&dwc->lock, flags);
		break;
	default:
		break;
	}

	spin_lock_irqsave(&dwc->lock, flags);

	dwc->current_otg_role = dwc->desired_otg_role;

	spin_unlock_irqrestore(&dwc->lock, flags);

	switch (dwc->desired_otg_role) {
	case DWC3_OTG_ROLE_HOST:
		spin_lock_irqsave(&dwc->lock, flags);
		dwc3_otgregs_init(dwc);
		dwc3_otg_host_init(dwc);
		spin_unlock_irqrestore(&dwc->lock, flags);
		ret = dwc3_host_init(dwc);
		if (ret) {
			dev_err(dwc->dev, "failed to initialize host\n");
		} else {
			if (dwc->usb2_phy)
				otg_set_vbus(dwc->usb2_phy->otg, true);
			if (dwc->usb2_generic_phy)
				phy_set_mode(dwc->usb2_generic_phy,
					     PHY_MODE_USB_HOST);
		}
		break;
	case DWC3_OTG_ROLE_DEVICE:
		spin_lock_irqsave(&dwc->lock, flags);
		dwc3_otgregs_init(dwc);
		dwc3_otg_device_init(dwc);
		dwc3_event_buffers_setup(dwc);
		spin_unlock_irqrestore(&dwc->lock, flags);

		if (dwc->usb2_phy)
			otg_set_vbus(dwc->usb2_phy->otg, false);
		if (dwc->usb2_generic_phy)
			phy_set_mode(dwc->usb2_generic_phy,
				     PHY_MODE_USB_DEVICE);
		ret = dwc3_gadget_init(dwc);
		if (ret)
			dev_err(dwc->dev, "failed to initialize peripheral\n");
		break;
	default:
		break;
	}
}

debugfs

drivers/usb/dwc3/debugfs.c通过应用层写模式到属性文件中，也能直接切换模式

static ssize_t dwc3_mode_write(struct file *file,
                const char __user *ubuf, size_t count, loff_t *ppos)
{
        struct seq_file         *s = file->private_data;
        struct dwc3             *dwc = s->private;
        u32                     mode = 0;
        char                    buf[32];

        if (copy_from_user(&buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
                return -EFAULT;

        if (!strncmp(buf, "host", 4))
                mode = DWC3_GCTL_PRTCAP_HOST;

        if (!strncmp(buf, "device", 6))
                mode = DWC3_GCTL_PRTCAP_DEVICE;

        if (!strncmp(buf, "otg", 3))
                mode = DWC3_GCTL_PRTCAP_OTG;

        dwc3_set_mode(dwc, mode);

        return count;
}