linux-kernel - Re: [linux-sunxi] [PATCH v2 9/9] power: supply: axp20x_usb

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Date:   Mon, 6 Jan 2020 12:27:01 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Sebastian Reichel <sre@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Oskari Lemmela <oskari@...mela.net>,
        Quentin Schulz <quentin.schulz@...tlin.com>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH v2 9/9] power: supply: axp20x_usb_power:
 Only poll while offline

On Sun, Jan 5, 2020 at 9:24 AM Samuel Holland <samuel@...lland.org> wrote:
>
> Investigation on the AXP803 shows that VBUS_PLUGIN/VBUS_REMOVAL IRQs are
> triggered on the rising/falling edge of AXP20X_PWR_STATUS_VBUS_USED. The
> reason IRQs do not arrive while N_VBUSEN/DRIVEVBUS is high is because
> AXP20X_PWR_STATUS_VBUS_USED also never goes high.
>
> This also means that if VBUS is online, a VBUS_REMOVAL IRQ is received
> immediately on setting N_VBUSEN/DRIVEVBUS high (and VBUS_PLUGIN shortly
> after it is set back low). This was also verified to be the case when
> manually offlining VBUS through AXP20X_VBUS_PATH_SELECT.
>
> As long as VBUS is online, a present->absent transition necessarily
> implies an online->offline transition. Since will cause an IRQ, there is
> no need to poll while VBUS is online.
>
> To ensure the driver's view of VBUS online status remains accurate,
> unconditionally poll once when receiving an IRQ and when resuming. If
> VBUS is still online at that time, polling will cease until the next
> VBUS_REMOVAL IRQ.
>
> Signed-off-by: Samuel Holland <samuel@...lland.org>

Reviewed-by: Chen-Yu Tsai <wens@...e.org>