Re: [PATCH v2 04/22] usb: dwc3: Add Apple Silicon DWC3 glue layer driver

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Sat, Sep 06, 2025, Sven Peter wrote:
> As mad as it sounds, the dwc3 controller present on the Apple M1 must be
> reset and reinitialized whenever a device is unplugged from the root
> port or when the PHY mode is changed.
> 
> This is required for at least the following reasons:
> 
>   - The USB2 D+/D- lines are connected through a stateful eUSB2 repeater
>     which in turn is controlled by a variant of the TI TPS6598x USB PD
>     chip. When the USB PD controller detects a hotplug event it resets
>     the eUSB2 repeater. Afterwards, no new device is recognized before
>     the DWC3 core and PHY are reset as well because the eUSB2 repeater
>     and the PHY/dwc3 block disagree about the current state.
> 
>   - It's possible to completely break the dwc3 controller by switching
>     it to device mode and unplugging the cable at just the wrong time.
>     If this happens dwc3 behaves as if no device is connected.
>     CORESOFTRESET will also never clear after it has been set. The only
>     workaround is to trigger a hard reset of the entire dwc3 core with
>     its external reset line.
> 
>   - Whenever the PHY mode is changed (to e.g. transition to DisplayPort
>     alternate mode or USB4) dwc3 has to be shutdown and reinitialized.
>     Otherwise the Type-C port will not be usable until the entire SoC
>     has been reset.
> 
> Additionally, these controllers have a Apple-specific MMIO region after
> the common dwc3 region where some controls have to be updated. PHY
> bringup and shutdown also requires SUSPHY to be enabled for the ports
> to work correctly.
> 
> In the future, this driver will also gain support for USB3-via-USB4
> tunneling which will require additional tweaks.
> 
> Add a glue driver that takes of all of these constraints.
> 
> Signed-off-by: Sven Peter <sven@kernel.org>
> ---
>  MAINTAINERS                   |   1 +
>  drivers/usb/dwc3/Kconfig      |  11 ++
>  drivers/usb/dwc3/Makefile     |   1 +
>  drivers/usb/dwc3/dwc3-apple.c | 425 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 438 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 0e085cb0762f765958d67be61ae0d3d773503431..e147e1b919d5737a34e684ec587872ce591c641a 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2424,6 +2424,7 @@ F:	drivers/pwm/pwm-apple.c
>  F:	drivers/soc/apple/*
>  F:	drivers/spi/spi-apple.c
>  F:	drivers/spmi/spmi-apple-controller.c
> +F:	drivers/usb/dwc3/dwc3-apple.c
>  F:	drivers/video/backlight/apple_dwi_bl.c
>  F:	drivers/watchdog/apple_wdt.c
>  F:	include/dt-bindings/interrupt-controller/apple-aic.h
> diff --git a/drivers/usb/dwc3/Kconfig b/drivers/usb/dwc3/Kconfig
> index 310d182e10b50b253d7e5a51674806e6ec442a2a..8161cd8f5d0d82826262518a1aefa3096aae83a8 100644
> --- a/drivers/usb/dwc3/Kconfig
> +++ b/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_APPLE
> +	tristate "Apple Silicon DWC3 Platform Driver"
> +	depends on OF && ARCH_APPLE
> +	default USB_DWC3
> +	select USB_ROLE_SWITCH
> +	help
> +	  Support Apple Silicon SoCs with DesignWare Core USB3 IP.
> +	  The DesignWare Core USB3 IP has to be used in dual-role
> +	  mode on these machines.
> +	  Say 'Y' or 'M' if you have such device.
> +
>  endif
> diff --git a/drivers/usb/dwc3/Makefile b/drivers/usb/dwc3/Makefile
> index 830e6c9e5fe073c1f662ce34b6a4a2da34c407a2..10b5e68cfd68d5ca9aa5a27b04f349f9bf58e65c 100644
> --- a/drivers/usb/dwc3/Makefile
> +++ b/drivers/usb/dwc3/Makefile
> @@ -43,6 +43,7 @@ endif
>  ##
>  
>  obj-$(CONFIG_USB_DWC3_AM62)		+= dwc3-am62.o
> +obj-$(CONFIG_USB_DWC3_APPLE)		+= dwc3-apple.o
>  obj-$(CONFIG_USB_DWC3_OMAP)		+= dwc3-omap.o
>  obj-$(CONFIG_USB_DWC3_EXYNOS)		+= dwc3-exynos.o
>  obj-$(CONFIG_USB_DWC3_PCI)		+= dwc3-pci.o
> diff --git a/drivers/usb/dwc3/dwc3-apple.c b/drivers/usb/dwc3/dwc3-apple.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..27674f0c284104cbbe75f51cd55593a964c8c9d6
> --- /dev/null
> +++ b/drivers/usb/dwc3/dwc3-apple.c
> @@ -0,0 +1,425 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Apple Silicon DWC3 Glue driver
> + * Copyright (C) The Asahi Linux Contributors
> + *
> + * Based on:
> + *  - dwc3-qcom.c Copyright (c) 2018, The Linux Foundation. All rights reserved.
> + *  - dwc3-of-simple.c Copyright (c) 2015 Texas Instruments Incorporated - https://urldefense.com/v3/__https://www.ti.com__;!!A4F2R9G_pg!Y-C3WLMl9OBFefTLBP84UnZJKzMKYzc7ZrG_bwC4q1q3h0XeGx8NmqFr_-FDYmDtHq802yjIffmSdYRaKA$ 
> + */
> +
> +#include <linux/of.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/platform_device.h>
> +#include <linux/reset.h>
> +
> +#include "glue.h"
> +
> +enum dwc3_apple_mode {
> +	DWC3_APPLE_OFF,
> +	DWC3_APPLE_HOST,
> +	DWC3_APPLE_DEVICE,
> +};
> +
> +/**
> + * struct dwc3_apple - Apple-specific DWC3 USB controller
> + * @dwc: Core DWC3 structure
> + * @dev: Pointer to the device structure
> + * @mmio_resource: Resource to be passed to dwc3_core_probe
> + * @apple_regs: Apple-specific DWC3 registers
> + * @resets: Reset control
> + * @role_sw: USB role switch
> + * @lock: Mutex for synchronizing access
> + * @core_probe_done: True if dwc3_core_probe was already called after the first plug
> + * @mode: Current mode of the controller (off/host/device)
> + */
> +struct dwc3_apple {
> +	struct dwc3 dwc;
> +
> +	struct device *dev;
> +	struct resource *mmio_resource;
> +	void __iomem *apple_regs;
> +
> +	struct reset_control *resets;
> +	struct usb_role_switch *role_sw;
> +
> +	struct mutex lock;
> +
> +	bool core_probe_done;
> +	enum dwc3_apple_mode mode;
> +};
> +
> +#define to_dwc3_apple(d) container_of((d), struct dwc3_apple, dwc)
> +
> +/*
> + * Apple Silicon dwc3 vendor-specific registers
> + *
> + * These registers were identified by tracing XNU's memory access patterns
> + * and correlating them with debug output over serial to determine their names.
> + * We don't exactly know what these do but without these USB3 devices sometimes
> + * don't work.
> + */
> +#define APPLE_DWC3_REGS_START 0xcd00
> +#define APPLE_DWC3_REGS_END 0xcdff
> +
> +#define APPLE_DWC3_CIO_LFPS_OFFSET 0xcd38
> +#define APPLE_DWC3_CIO_LFPS_OFFSET_VALUE 0xf800f80
> +
> +#define APPLE_DWC3_CIO_BW_NGT_OFFSET 0xcd3c
> +#define APPLE_DWC3_CIO_BW_NGT_OFFSET_VALUE 0xfc00fc0
> +
> +#define APPLE_DWC3_CIO_LINK_TIMER 0xcd40
> +#define APPLE_DWC3_CIO_PENDING_HP_TIMER GENMASK(23, 16)
> +#define APPLE_DWC3_CIO_PENDING_HP_TIMER_VALUE 0x14
> +#define APPLE_DWC3_CIO_PM_LC_TIMER GENMASK(15, 8)
> +#define APPLE_DWC3_CIO_PM_LC_TIMER_VALUE 0xa
> +#define APPLE_DWC3_CIO_PM_ENTRY_TIMER GENMASK(7, 0)
> +#define APPLE_DWC3_CIO_PM_ENTRY_TIMER_VALUE 0x10
> +
> +static inline void dwc3_apple_writel(struct dwc3_apple *appledwc, u32 offset, u32 value)
> +{
> +	writel(value, appledwc->apple_regs + offset - APPLE_DWC3_REGS_START);
> +}
> +
> +static inline u32 dwc3_apple_readl(struct dwc3_apple *appledwc, u32 offset)
> +{
> +	return readl(appledwc->apple_regs + offset - APPLE_DWC3_REGS_START);
> +}
> +
> +static inline void dwc3_apple_mask(struct dwc3_apple *appledwc, u32 offset, u32 mask, u32 value)
> +{
> +	u32 reg;
> +
> +	reg = dwc3_apple_readl(appledwc, offset);
> +	reg &= ~mask;
> +	reg |= value;
> +	dwc3_apple_writel(appledwc, offset, reg);
> +}
> +
> +static void dwc3_apple_setup_cio(struct dwc3_apple *appledwc)
> +{
> +	dwc3_apple_writel(appledwc, APPLE_DWC3_CIO_LFPS_OFFSET, APPLE_DWC3_CIO_LFPS_OFFSET_VALUE);
> +	dwc3_apple_writel(appledwc, APPLE_DWC3_CIO_BW_NGT_OFFSET,
> +			  APPLE_DWC3_CIO_BW_NGT_OFFSET_VALUE);
> +	dwc3_apple_mask(appledwc, APPLE_DWC3_CIO_LINK_TIMER, APPLE_DWC3_CIO_PENDING_HP_TIMER,
> +			APPLE_DWC3_CIO_PENDING_HP_TIMER_VALUE);
> +	dwc3_apple_mask(appledwc, APPLE_DWC3_CIO_LINK_TIMER, APPLE_DWC3_CIO_PM_LC_TIMER,
> +			APPLE_DWC3_CIO_PM_LC_TIMER_VALUE);
> +	dwc3_apple_mask(appledwc, APPLE_DWC3_CIO_LINK_TIMER, APPLE_DWC3_CIO_PM_ENTRY_TIMER,
> +			APPLE_DWC3_CIO_PM_ENTRY_TIMER_VALUE);
> +}
> +
> +static void dwc3_apple_set_ptrcap(struct dwc3_apple *appledwc, u32 mode)
> +{
> +	guard(spinlock_irqsave)(&appledwc->dwc.lock);
> +	dwc3_set_prtcap(&appledwc->dwc, mode, false);
> +}
> +
> +static int dwc3_apple_core_probe(struct dwc3_apple *appledwc)
> +{
> +	struct dwc3_probe_data probe_data = {};
> +	int ret;
> +
> +	lockdep_assert_held(&appledwc->lock);
> +	WARN_ON_ONCE(appledwc->core_probe_done);
> +
> +	appledwc->dwc.dev = appledwc->dev;
> +	probe_data.dwc = &appledwc->dwc;
> +	probe_data.res = appledwc->mmio_resource;
> +	probe_data.ignore_clocks_and_resets = true;
> +	probe_data.skip_core_init_mode = true;
> +
> +	ret = dwc3_core_probe(&probe_data);
> +	if (ret)
> +		return ret;
> +
> +	appledwc->core_probe_done = true;
> +	return 0;
> +}
> +
> +static int dwc3_apple_core_init(struct dwc3_apple *appledwc)
> +{
> +	int ret;
> +
> +	lockdep_assert_held(&appledwc->lock);
> +
> +	if (appledwc->core_probe_done) {
> +		ret = dwc3_core_init(&appledwc->dwc);
> +		if (ret)
> +			dev_err(appledwc->dev, "Failed to initialize DWC3 Core, err=%d\n", ret);
> +	} else {
> +		ret = dwc3_apple_core_probe(appledwc);
> +		if (ret)
> +			dev_err(appledwc->dev, "Failed to probe DWC3 Core, err=%d\n", ret);
> +	}
> +
> +	return ret;
> +}
> +
> +static void dwc3_apple_phy_set_mode(struct dwc3_apple *appledwc, enum phy_mode mode)
> +{
> +	lockdep_assert_held(&appledwc->lock);
> +
> +	/*
> +	 * This platform requires SUSPHY to be enabled here already in order to properly
> +	 * configure the PHY
> +	 */
> +	dwc3_enable_susphy(&appledwc->dwc, true);
> +	phy_set_mode(appledwc->dwc.usb2_generic_phy[0], mode);
> +	phy_set_mode(appledwc->dwc.usb3_generic_phy[0], mode);
> +}
> +
> +static int dwc3_apple_init(struct dwc3_apple *appledwc, enum dwc3_apple_mode mode)
> +{
> +	int ret, ret_reset;
> +
> +	lockdep_assert_held(&appledwc->lock);
> +
> +	ret = reset_control_deassert(appledwc->resets);
> +	if (ret) {
> +		dev_err(appledwc->dev, "Failed to deassert resets, err=%d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = dwc3_apple_core_init(appledwc);
> +	if (ret)
> +		goto reset_assert;
> +
> +	/*
> +	 * Now that the core is initialized and already went through dwc3_core_soft_reset we can
> +	 * configure some unknown Apple-specific settings.
> +	 */
> +	dwc3_apple_setup_cio(appledwc);
> +
> +	switch (mode) {
> +	case DWC3_APPLE_HOST:
> +		appledwc->dwc.dr_mode = USB_DR_MODE_HOST;
> +		dwc3_apple_set_ptrcap(appledwc, DWC3_GCTL_PRTCAP_HOST);
> +		dwc3_apple_phy_set_mode(appledwc, PHY_MODE_USB_HOST);
> +		ret = dwc3_host_init(&appledwc->dwc);
> +		if (ret) {
> +			dev_err(appledwc->dev, "Failed to initialize host, ret=%d\n", ret);
> +			goto core_exit;
> +		}
> +
> +		break;
> +	case DWC3_APPLE_DEVICE:
> +		appledwc->dwc.dr_mode = USB_DR_MODE_PERIPHERAL;
> +		dwc3_apple_set_ptrcap(appledwc, DWC3_GCTL_PRTCAP_DEVICE);
> +		dwc3_apple_phy_set_mode(appledwc, PHY_MODE_USB_DEVICE);
> +		ret = dwc3_gadget_init(&appledwc->dwc);
> +		if (ret) {
> +			dev_err(appledwc->dev, "Failed to initialize gadget, ret=%d\n", ret);
> +			goto core_exit;
> +		}
> +		break;
> +	default:
> +		/* Unreachable unless there's a bug in this driver */
> +		WARN_ON_ONCE(1);
> +		ret = -EINVAL;
> +		goto core_exit;
> +	}
> +
> +	appledwc->mode = mode;
> +	return 0;
> +
> +core_exit:
> +	dwc3_core_exit(&appledwc->dwc);
> +reset_assert:
> +	ret_reset = reset_control_assert(appledwc->resets);
> +	if (ret_reset)
> +		dev_warn(appledwc->dev, "Failed to assert resets, err=%d\n", ret_reset);
> +
> +	return ret;
> +}
> +
> +static int dwc3_apple_exit(struct dwc3_apple *appledwc)
> +{
> +	int ret = 0;
> +
> +	lockdep_assert_held(&appledwc->lock);
> +
> +	switch (appledwc->mode) {
> +	case DWC3_APPLE_OFF:
> +		/* Nothing to do if we're already off */
> +		return 0;
> +	case DWC3_APPLE_DEVICE:
> +		dwc3_gadget_exit(&appledwc->dwc);
> +		break;
> +	case DWC3_APPLE_HOST:
> +		dwc3_host_exit(&appledwc->dwc);
> +		break;
> +	}
> +
> +	/* This platform requires SUSPHY to be enabled in order to properly power down the PHY */
> +	dwc3_enable_susphy(&appledwc->dwc, true);
> +	dwc3_core_exit(&appledwc->dwc);
> +	appledwc->mode = DWC3_APPLE_OFF;
> +
> +	ret = reset_control_assert(appledwc->resets);
> +	if (ret) {
> +		dev_err(appledwc->dev, "Failed to assert resets, err=%d\n", ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int dwc3_usb_role_switch_set(struct usb_role_switch *sw, enum usb_role role)
> +{
> +	struct dwc3_apple *appledwc = usb_role_switch_get_drvdata(sw);
> +	int ret;
> +
> +	guard(mutex)(&appledwc->lock);
> +
> +	/*
> +	 * The USB2 D+/D- lines are connected through a stateful eUSB2 repeater which in turn is
> +	 * controlled by a variant of the TI TPS6598x USB PD chip. When the USB PD controller
> +	 * detects a hotplug event it resets the eUSB2 repeater. Afterwards, no new device is
> +	 * recognized before the DWC3 core and PHY are reset as well because the eUSB2 repeater
> +	 * and the PHY/dwc3 block disagree about the current state.
> +	 * Additionally, the PHY is also incapable of switching between arbitrary modes when dwc3
> +	 * is kept online. It's also possible to get dwc3 into a state where no new device is
> +	 * recognized and even a soft reset is not enough to recover when unplugging a cable at the
> +	 * wrong time while in gadget mode. Only a hard reset triggered via the external reset line
> +	 * is able to recover from this state.
> +	 * We thus tear all of dwc3 down here and re-initialize it every time we get a plug change
> +	 * (or even mode change) event.
> +	 */
> +	ret = dwc3_apple_exit(appledwc);
> +	if (ret)
> +		return ret;
> +
> +	switch (role) {
> +	case USB_ROLE_NONE:
> +		/* Nothing to do if no cable is connected */
> +		return 0;
> +	case USB_ROLE_HOST:
> +		return dwc3_apple_init(appledwc, DWC3_APPLE_HOST);
> +	case USB_ROLE_DEVICE:
> +		return dwc3_apple_init(appledwc, DWC3_APPLE_DEVICE);
> +	default:
> +		dev_err(appledwc->dev, "Invalid target role: %d\n", role);
> +		return -EINVAL;
> +	}
> +}
> +
> +static enum usb_role dwc3_usb_role_switch_get(struct usb_role_switch *sw)
> +{
> +	struct dwc3_apple *appledwc = usb_role_switch_get_drvdata(sw);
> +
> +	guard(mutex)(&appledwc->lock);
> +
> +	switch (appledwc->mode) {
> +	case DWC3_APPLE_HOST:
> +		return USB_ROLE_HOST;
> +	case DWC3_APPLE_DEVICE:
> +		return USB_ROLE_DEVICE;
> +	case DWC3_APPLE_OFF:
> +		return USB_ROLE_NONE;
> +	default:
> +		/* Unreachable unless there's a bug in this driver */
> +		WARN_ON_ONCE(1);
> +		return USB_ROLE_NONE;
> +	}
> +}
> +
> +static int dwc3_apple_setup_role_switch(struct dwc3_apple *appledwc)
> +{
> +	struct usb_role_switch_desc dwc3_role_switch = { NULL };
> +
> +	dwc3_role_switch.fwnode = dev_fwnode(appledwc->dev);
> +	dwc3_role_switch.set = dwc3_usb_role_switch_set;
> +	dwc3_role_switch.get = dwc3_usb_role_switch_get;
> +	dwc3_role_switch.driver_data = appledwc;
> +	appledwc->role_sw = usb_role_switch_register(appledwc->dev, &dwc3_role_switch);
> +	if (IS_ERR(appledwc->role_sw))
> +		return PTR_ERR(appledwc->role_sw);
> +
> +	return 0;
> +}
> +
> +static int dwc3_apple_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct dwc3_apple *appledwc;
> +	int ret;
> +
> +	appledwc = devm_kzalloc(&pdev->dev, sizeof(*appledwc), GFP_KERNEL);
> +	if (!appledwc)
> +		return -ENOMEM;
> +
> +	appledwc->dev = &pdev->dev;
> +	mutex_init(&appledwc->lock);
> +
> +	appledwc->resets = devm_reset_control_array_get_exclusive(dev);
> +	if (IS_ERR(appledwc->resets))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(appledwc->resets),
> +				     "Failed to get resets\n");
> +
> +	ret = reset_control_assert(appledwc->resets);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Failed to assert resets, err=%d\n", ret);
> +		return ret;
> +	}
> +
> +	appledwc->mmio_resource = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dwc3-core");
> +	if (!appledwc->mmio_resource) {
> +		dev_err(dev, "Failed to get DWC3 MMIO\n");
> +		return -EINVAL;
> +	}
> +
> +	appledwc->apple_regs = devm_platform_ioremap_resource_byname(pdev, "dwc3-apple");
> +	if (IS_ERR(appledwc->apple_regs))
> +		return dev_err_probe(dev, PTR_ERR(appledwc->apple_regs),
> +				     "Failed to map Apple-specific MMIO\n");
> +
> +	/*
> +	 * Note that we only bring up dwc3 once the first device is attached because we need to know
> +	 * the role (e.g. host), mode (e.g. USB3) and lane orientation to bring up the PHY which is
> +	 * tightly coupled to dwc3.
> +	 */
> +	appledwc->mode = DWC3_APPLE_OFF;
> +	appledwc->core_probe_done = false;
> +	ret = dwc3_apple_setup_role_switch(appledwc);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret, "Failed to setup role switch\n");
> +
> +	return 0;
> +}
> +
> +static void dwc3_apple_remove(struct platform_device *pdev)
> +{
> +	struct dwc3 *dwc = platform_get_drvdata(pdev);
> +	struct dwc3_apple *appledwc = to_dwc3_apple(dwc);
> +
> +	guard(mutex)(&appledwc->lock);
> +
> +	usb_role_switch_unregister(appledwc->role_sw);
> +
> +	dwc3_apple_exit(appledwc);
> +	if (appledwc->core_probe_done)
> +		dwc3_core_remove(&appledwc->dwc);
> +}
> +
> +static const struct of_device_id dwc3_apple_of_match[] = {
> +	{ .compatible = "apple,t8103-dwc3" },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, dwc3_apple_of_match);
> +
> +static struct platform_driver dwc3_apple_driver = {
> +	.probe		= dwc3_apple_probe,
> +	.remove		= dwc3_apple_remove,
> +	.driver		= {
> +		.name	= "dwc3-apple",
> +		.of_match_table	= dwc3_apple_of_match,
> +	},
> +};
> +
> +module_platform_driver(dwc3_apple_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Sven Peter <sven@kernel.org>");
> +MODULE_DESCRIPTION("DesignWare DWC3 Apple Silicon Glue Driver");
> 
> -- 
> 2.34.1
> 
> 

I like these new changes! From the quick glance, this looks good to me.

Sorry for the delay, but I need get back to reviewing this in detail
next week.

BR,
Thinh