linux-kernel - Re: [PATCH v2 2/2] Input: atmel_mxt_ts - wake mXT1386 from deep-sleep mode

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Message-ID: <11e0052b-ae7a-71bc-1b28-9d5b42acfd11@gmail.com>
Date:   Sat, 19 Sep 2020 22:49:07 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     "Wang, Jiada" <jiada_wang@...tor.com>, nick@...anahar.org,
        dmitry.torokhov@...il.com, robh+dt@...nel.org
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        andy.shevchenko@...il.com, erosca@...adit-jv.com,
        Andrew_Gabbasov@...tor.com
Subject: Re: [PATCH v2 2/2] Input: atmel_mxt_ts - wake mXT1386 from deep-sleep
 mode

18.09.2020 18:55, Wang, Jiada пишет:
...
>>>   +static void mxt_wake(struct mxt_data *data)
>>> +{
>>> +    struct i2c_client *client = data->client;
>>> +    struct device *dev = &data->client->dev;
>>> +    struct device_node *np = dev->of_node;
>>> +    union i2c_smbus_data dummy;
>>> +
>>> +    if (!of_device_is_compatible(np, "atmel,mXT1386"))
>>> +        return;
>> I'm not sure whether you misses the previous answers from Dmitry
>> Torokhov and Rob Herring, but they suggested to add a new device-tree
>> property which should specify the atmel,wakeup-method.
>>
> I think Rob Herring prefers for the compatible solution than property.

Actually, seems you're right. But I'm not sure now whether he just made
a typo, because it's actually a board-specific option.

It could be more preferred to skip the i2c_smbus_xfer() for the NONE
variant, but it also should be harmless in practice. I guess we indeed
could keep the current variant of yours patch and then add a clarifying
comment to the commit message and to the code, telling that
i2c_smbus_xfer() is harmless in a case of the hardwired WAKE-LINE.

>> There are 3 possible variants:
>>
>>    - NONE
>>    - GPIO
>>    - I2C-SCL
>>
>> Hence we should bail out from mxt_wake() if method is set to NONE or
>> GPIO.
>>
> for "GPIO", we still need 25 ms sleep. but rather than a dummy read,
> WAKE line need to be asserted before sleep.

Correct, I just meant to bail out because GPIO is currently unsupported.

...
>>>   static int mxt_initialize(struct mxt_data *data)
>>>   {
>>>       struct i2c_client *client = data->client;
>>>       int recovery_attempts = 0;
>>>       int error;
>>>   +    mxt_wake(data);
>>> +
>>>       while (1) {
>>
>> I assume the mxt_wake() should be placed here, since there is a 3
>> seconds timeout in the end of the while-loop, meaning that device may
>> get back into deep-sleep on a retry.
>>
> Can you elaborate a little more why exit from bootload mode after sleep
> for 3 second could enter deep-sleep mode.

The loop attempts to exit from bootload mode and then I suppose
mxt_read_info_block() may fail if I2C "accidentally" fails, hence the
deep-sleep mode still will be enabled on a retry.

The datasheet says that there are 2 seconds since the time of the last
I2C access before TS is put back into auto-sleep if deep-sleep mode is
enabled. The wait-loop has msleep(3000).