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Subject: Re: [PATCH v1 1/2] usb: phy: tegra: Wait for VBUS wakeup status
 deassertion on suspend
To:     Peter Chen <peter.chen@kernel.org>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>,
        Maxim Schwalm <maxim.schwalm@gmail.com>,
        linux-tegra@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210613145936.9902-1-digetx@gmail.com>
 <20210615010516.GA28352@nchen>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <b00a214c-02dd-9cc5-ff6f-acfd19841528@gmail.com>
Date:   Tue, 15 Jun 2021 17:48:06 +0300
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15.06.2021 04:05, Peter Chen пишет:
> On 21-06-13 17:59:35, Dmitry Osipenko wrote:
>> Some devices need an extra delay after losing VBUS, otherwise VBUS may
>> be detected as active at suspend time, preventing the PHY's suspension
>> by the VBUS detection sensor. This problem was found on Asus Transformer
>> TF700T (Tegra30) tablet device, where the USB PHY wakes up immediately
>> from suspend because VBUS sensor continues to detect VBUS as active after
>> disconnection. We need to poll the PHY's VBUS wakeup status until it's
>> deasserted before suspending PHY in order to fix this minor trouble.
>>
>> Fixes: 35192007d28d ("usb: phy: tegra: Support waking up from a low power mode")
>> Reported-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
>> Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>> ---
>>  drivers/usb/phy/phy-tegra-usb.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/usb/phy/phy-tegra-usb.c b/drivers/usb/phy/phy-tegra-usb.c
>> index fc5c6cab58ba..ff482c694200 100644
>> --- a/drivers/usb/phy/phy-tegra-usb.c
>> +++ b/drivers/usb/phy/phy-tegra-usb.c
>> @@ -64,6 +64,7 @@
>>  #define   A_VBUS_VLD_WAKEUP_EN			BIT(30)
>>  
>>  #define USB_PHY_VBUS_WAKEUP_ID			0x408
>> +#define   VBUS_WAKEUP_STS			BIT(10)
>>  #define   VBUS_WAKEUP_WAKEUP_EN			BIT(30)
>>  
>>  #define USB1_LEGACY_CTRL			0x410
>> @@ -645,6 +646,15 @@ static int utmi_phy_power_off(struct tegra_usb_phy *phy)
>>  	void __iomem *base = phy->regs;
>>  	u32 val;
>>  
>> +	/*
>> +	 * Give hardware time to settle down after VBUS disconnection,
>> +	 * otherwise PHY will immediately wake up from suspend.
>> +	 */
>> +	if (phy->wakeup_enabled && phy->mode != USB_DR_MODE_HOST)
>> +		readl_relaxed_poll_timeout(base + USB_PHY_VBUS_WAKEUP_ID,
>> +					   val, !(val & VBUS_WAKEUP_STS),
>> +					   5000, 100000);
>> +
> 
> Where will clear VBUS_WAKEUP_STS? Or it will be cleared by HW after VBUS lower than
> B Session Valid?

It's cleared by hardware. Tegra documentation doesn't explicitly saying
what voltage level is used by the VBUS_WAKEUP sensor, but it implies the
session-valid level.

There are two sensors that could be used for detection of
cable-insertion into B-device USB port of Tegra: VBUS_WAKEUP and
A_SESS_VLD (from perspective of Tegra as a B-device).

The VBUS_WAKEUP sensor may not work in some hardware configurations,
always outputting 0. Seems it depends on whether port is OTG-capable
(VBUS_WAKEUP works) or fixed to a device mode. IIUC, only VBUS_WAKEUP
sensor can generate wake event that can resume system for a deepest
suspend state.