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

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Message-ID: <e9f18b0d-6462-43e7-955f-45337914b321@nvidia.com>
Date: Tue, 13 Jan 2026 11:35:18 +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 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 ...

   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.

Jon

-- 
nvpublic