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

[Diogo Ivo]

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@xxxxxxxxxxxxxxxxxx>
> > > ---
> > >   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