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

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Date:   Sun, 6 Dec 2020 22:42:37 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
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

06.12.2020 18:20, Linus Walleij пишет:
> 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.

Still it's better than a disfunctional hardware :)

> 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.

I don't have hardware which uses the wake-gpio in order to test that it
works properly, hence wanted to keep it minimal. But indeed sounds like
toggling the GPIO in suspend/resume should be okay to do. Alright, I'll
improve it in the v3. Thank you!