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

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Message-ID: <6a0d379f-d215-4efc-bdd0-c9a74d31614a@nvidia.com>
Date: Tue, 13 Jan 2026 11:44:51 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>,
 Mathias Nyman <mathias.nyman@...el.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Thierry Reding <thierry.reding@...il.com>, JC Kuo <jckuo@...dia.com>,
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>
Cc: linux-usb@...r.kernel.org, linux-tegra@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH 3/5] phy: tegra: xusb: Fix ordering issue when switching
 roles on USB2 ports


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@...nico.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.

Nonetheless this needs to be fixed.

Jon

-- 
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