Re: [PATCH 3/5] phy: tegra: xusb: Fix ordering issue when switching roles on USB2 ports

Diogo Ivo
2026-01-13T13:59:46Z

On 1/13/26 11:44, Jon Hunter wrote:
>
> On 13/01/2026 11:35, Jon Hunter wrote:
>>
>> On 04/12/2025 21:27, Diogo Ivo wrote:
>>> The current implementation of USB2 role switching on Tegra relies on
>>> whichever the previous USB controller driver was using the PHY to first
>>> "yield" it back to USB_ROLE_NONE before the next controller configures
>>> it for the new role. However, no mechanism to guarantee this ordering
>>> was implemented, and currently, in the general case, the configuration
>>> functions tegra_xhci_id_work() and tegra_xudc_usb_role_sw_work() end up
>>> running in the same order regardless of the transition being HOST-
>>> >DEVICE
>>> or DEVICE->HOST, leading to one of these transitions ending up in a
>>> non-working state due to the new configuration being clobbered by the
>>> previous controller driver setting USB_ROLE_NONE after the fact.
>>>
>>> Fix this by introducing a helper that waits for the USB2 port’s current
>>> role to become USB_ROLE_NONE and add it in the configuration functions
>>> above before setting the role to either USB_ROLE_HOST or
>>> USB_ROLE_DEVICE. The specific parameters of the helper function are
>>> choices that seem reasonable in my testing and have no other basis.
>>>
>>> This was tested on a Tegra210 platform (Smaug). However, due to the
>>> similar
>>> approach in Tegra186 it is likely that not only this problem exists
>>> there
>>> but that this patch also fixes it.
>>>
>>> Signed-off-by: Diogo Ivo <diogo.ivo@tecnico.ulisboa.pt>
>>> ---
>>> drivers/phy/tegra/xusb.c | 23 +++++++++++++++++++++++
>>> drivers/usb/gadget/udc/tegra-xudc.c | 4 ++++
>>> drivers/usb/host/xhci-tegra.c | 15 ++++++++++-----
>>> include/linux/phy/tegra/xusb.h | 1 +
>>> 4 files changed, 38 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/phy/tegra/xusb.c b/drivers/phy/tegra/xusb.c
>>> index c89df95aa6ca..e05c3f2d1421 100644
>>> --- a/drivers/phy/tegra/xusb.c
>>> +++ b/drivers/phy/tegra/xusb.c
>>> @@ -740,6 +740,29 @@ static void
>>> tegra_xusb_parse_usb_role_default_mode(struct tegra_xusb_port *port)
>>> }
>>> }
>>> +bool tegra_xusb_usb2_port_wait_role_none(struct tegra_xusb_padctl
>>> *padctl, int index)
>>> +{
>>> + struct tegra_xusb_usb2_port *usb2 =
>>> tegra_xusb_find_usb2_port(padctl,
>>> + index);
>>> + int retries = 5;
>>> +
>>> + if (!usb2) {
>>> + dev_err(&usb2->base.dev, "no port found for USB2 lane %u\n",
>>> index);
>>> + return false;
>>> + }
>>> +
>>> + do {
>>> + if (usb2->role == USB_ROLE_NONE)
>>> + return true;
>>> +
>>> + usleep_range(50, 60);
>>> + } while (retries--);
>>> +
>>> + dev_err(&usb2->base.dev, "timed out waiting for USB_ROLE_NONE");
>>> +
>>> + return false;
>>> +}
>>
>>
>> This patch is causing the following build error today with -next ...
>
> Sorry this is not in -next, I had just applied locally on top!
>
>> MODPOST Module.symvers
>> ERROR: modpost: "tegra_xusb_usb2_port_wait_role_none" [drivers/usb/
>> host/ xhci-tegra.ko] undefined!
>>
>> The above function symbol needs to be exported.

You're right, thanks for catching this. I'll fix it in v2.

>
> Nonetheless this needs to be fixed.
>
> Jon
>