linux-kernel - Re: [PATCH 2/5] phy: tegra: xusb: Fix USB2 port regulator disable logic

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Message-ID: <c5450fc7-230e-4435-bd1d-3db4f1f6e736@nvidia.com>
Date: Tue, 13 Jan 2026 12:01:38 +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 2/5] phy: tegra: xusb: Fix USB2 port regulator disable
 logic


On 04/12/2025 21:27, Diogo Ivo wrote:
> The USB2 PHY mode handling on Tegra210 incorrectly relied on
> regulator_is_enabled() when determining whether the VBUS supply should
> be disabled during role changes. This is because regulator_is_enabled()
> reports exactly what is states and not if there is an unbalanced number
> of calls between regulator_enable() and regulator_disable(). For
> example, regulator_is_enabled() always reports true on a fixed-regulator
> with no enable gpio, which is the case on the Pixel C.
> 
> This then leads to the PHY driver wrongfully calling regulator_disable()
> when transitioning from USB_ROLE_DEVICE to USB_ROLE_NONE since the driver
> did not previously call the corresponding regulator_enable().
> 
> Fix this by keeping track of the current role and updating the logic to
> disable the regulator only when the previous role was USB_ROLE_HOST.
> 
> While at it fix a small typo in a comment.
> 
> Signed-off-by: Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>
> ---
>   drivers/phy/tegra/xusb-tegra210.c | 5 +++--
>   drivers/phy/tegra/xusb.h          | 1 +
>   2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/phy/tegra/xusb-tegra210.c b/drivers/phy/tegra/xusb-tegra210.c
> index 3409924498e9..63ad57d95514 100644
> --- a/drivers/phy/tegra/xusb-tegra210.c
> +++ b/drivers/phy/tegra/xusb-tegra210.c
> @@ -1934,9 +1934,9 @@ static int tegra210_usb2_phy_set_mode(struct phy *phy, enum phy_mode mode,
>   			/*
>   			 * When port is peripheral only or role transitions to
>   			 * USB_ROLE_NONE from USB_ROLE_DEVICE, regulator is not
> -			 * be enabled.
> +			 * enabled.
>   			 */
> -			if (regulator_is_enabled(port->supply))
> +			if (port->role == USB_ROLE_HOST)
>   				regulator_disable(port->supply);
>   
>   			tegra210_xusb_padctl_id_override(padctl, false);
> @@ -1944,6 +1944,7 @@ static int tegra210_usb2_phy_set_mode(struct phy *phy, enum phy_mode mode,
>   		}
>   	}
>   
> +	port->role = submode;
>   	mutex_unlock(&padctl->lock);
>   
>   	return err;
> diff --git a/drivers/phy/tegra/xusb.h b/drivers/phy/tegra/xusb.h
> index d2b5f9565132..273af147dfd3 100644
> --- a/drivers/phy/tegra/xusb.h
> +++ b/drivers/phy/tegra/xusb.h
> @@ -317,6 +317,7 @@ struct tegra_xusb_usb2_port {
>   	enum usb_dr_mode mode;
>   	bool internal;
>   	int usb3_port_fake;
> +	enum usb_role role;
>   };


A similar fix was made to the Tegra186 code by commit cefc1caee9dd 
("phy: tegra: xusb: Fix unbalanced regulator disable in UTMI PHY mode"). 
Although the above looks simpler, I am wondering if we should make a 
similar change to the Tegra210 code so that they both are implemented in 
the same way?

Jon
-- 
nvpublic