On Sun, Aug 24, 2025, Janne Grunau wrote:

On Thu, Aug 21, 2025 at 11:25:51PM +0000, Thinh Nguyen wrote:

quoted

On Thu, Aug 21, 2025, Sven Peter wrote:

quoted

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.

All of this can be easily worked around by respecting transitions to
USB_ROLE_NONE and making sure the external reset line is asserted when
switching roles. We additionally have to ensure that the PHY is
suspended during init.

Signed-off-by: Sven Peter <sven@kernel.org>
---
 drivers/usb/dwc3/core.c | 61 +++++++++++++++++++++++++++++++++++++++++++++----
 drivers/usb/dwc3/core.h |  3 +++
 drivers/usb/dwc3/drd.c  | 11 ++++++++-
 drivers/usb/dwc3/host.c |  3 ++-
 4 files changed, 72 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 8002c23a5a02acb8f3e87b2662a53998a4cf4f5c..26aa507a738f001409a97ef563c6561433a1cac5 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c

...

quoted

quoted

 	/*
 	 * When current_dr_role is not set, there's no role switching.
 	 * Only perform GCTL.CoreSoftReset when there's DRD role switching.
 	 */
-	if (dwc->current_dr_role && ((DWC3_IP_IS(DWC3) ||
+	if (dwc->role_switch_reset_quirk ||

Don't override the use of GCTL.CoreSoftReset with this quirk. Not all
controller versions should use GCTL.CoreSoftReset, the new controller
version don't even have it. What version is this vendor using?

It reports DWC31, revision 190A and the unlisted version_types
0x736f3035 (M1), 0x736f3039 (M1 Pro/Max/Ultra) and 0x736f3130 (M2, M2
Pro/Max/Ultra).

Thanks for the info. This version should not be using
GCTL.CoreSoftReset.

BR,
Thinh