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

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Message-ID: <043663d0-d592-432b-8550-10669674d17a@nvidia.com>
Date: Tue, 13 Jan 2026 14:42:07 +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 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.

Jon

-- 
nvpublic