linux-kernel - Re: [PATCH v2 2/3] Input: atmel_mxt_ts

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Message-ID: <CACRpkdZoxsamwCpckeMOVSkK_DQOqakmZ3fHzYb8CeSGZ1V_NA@mail.gmail.com>
Date:   Sun, 6 Dec 2020 16:20:28 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Nick Dyer <nick@...anahar.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Jiada Wang <jiada_wang@...tor.com>,
        Linux Input <linux-input@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] Input: atmel_mxt_ts - support wakeup methods

On Sat, Dec 5, 2020 at 6:48 AM Dmitry Osipenko <digetx@...il.com> wrote:

> According to datasheets, chips like mXT1386 have a WAKE line, it is used
> to wake the chip up from deep sleep mode before communicating with it via
> the I2C-compatible interface.
>
> If the WAKE line is connected to a GPIO line, the line must be asserted
> 25 ms before the host attempts to communicate with the controller. If the
> WAKE line is connected to the SCL pin, the controller will send a NACK on
> the first attempt to address it, the host must then retry 25 ms later.
>
> Implement the wake-up methods in the driver. Touchscreen now works
> properly on devices like Acer A500 tablet, fixing problems like this:
>
>  atmel_mxt_ts 0-004c: __mxt_read_reg: i2c transfer failed (-121)
>  atmel_mxt_ts 0-004c: mxt_bootloader_read: i2c recv failed (-121)
>  atmel_mxt_ts 0-004c: Trying alternate bootloader address
>  atmel_mxt_ts 0-004c: mxt_bootloader_read: i2c recv failed (-121)
>  atmel_mxt_ts: probe of 0-004c failed with error -121
>
> Signed-off-by: Jiada Wang <jiada_wang@...tor.com>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>

OK looks interesting!

> +       /* Request the WAKE line as asserted so controller won't sleep */
> +       data->wake_gpio = devm_gpiod_get_optional(&client->dev,
> +                                                 "wake", GPIOD_OUT_HIGH);
> +       if (IS_ERR(data->wake_gpio)) {
> +               error = PTR_ERR(data->wake_gpio);
> +               dev_err(&client->dev, "Failed to get wake gpio: %d\n", error);
> +               return error;
> +       }

That is a bit brutal, don't you think? Now you force the controller
to be on at all times. Even across suspend/resume.

Shouldn't the same patch drive this low in mxt_suspend()
and driver it high + wait 25 ms in mxt_resume()?
Waiting 25ms in mxt_resume() is chill, it is anyway on the
slowpath.

Yours,
Linus Walleij