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

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Message-ID: <f942f18f-76f7-477d-8861-6e9d1a29655c@tecnico.ulisboa.pt>
Date: Tue, 13 Jan 2026 15:05:16 +0000
From: Diogo Ivo <diogo.ivo@...nico.ulisboa.pt>
To: Jon Hunter <jonathanh@...dia.com>, 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 1/13/26 14:42, Jon Hunter wrote:
> 
> On 13/01/2026 13:59, Diogo Ivo wrote:
>>
>>
>> On 1/13/26 12:01, Jon Hunter wrote:
>>>
>>> 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?
>>
>> Looking at cefc1caee9dd my approach leads to less changes but I do agree
>> that standardization benefits us here. However in that case I think we
>> can take it a step further and actually just have a single function
>> tegra_xusb_padctl_id_override() (and likewise for vbus_override() and
>> set_mode()) since they all seem to do the same thing in both platforms.
> 
> Yes I think that would be fine. I can't say I have looked at that in 
> detail but that would seem like the logical way to go.

Ok, then I'll do just that.

> Jon