linux-kernel - Re: [PATCH v1 1/2] usb: phy: tegra: Wait for VBUS wakeup status deassertion on suspend

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Message-ID: <20210615010516.GA28352@nchen>
Date:   Tue, 15 Jun 2021 09:05:16 +0800
From:   Peter Chen <peter.chen@...nel.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        linux-tegra@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] usb: phy: tegra: Wait for VBUS wakeup status
 deassertion on suspend

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@...il.com> # Asus TF700T
> Tested-by: Maxim Schwalm <maxim.schwalm@...il.com> # Asus TF700T
> Signed-off-by: Dmitry Osipenko <digetx@...il.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?

-- 

Thanks,
Peter Chen