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SubjectRe: [PATCH v4 1/1] Input: atmel_mxt_ts - implement I2C retries
14.09.2020 22:36, Dmitry Torokhov пишет:
> On Mon, Sep 14, 2020 at 12:33:40PM -0700, Dmitry Torokhov wrote:
>> On Mon, Sep 14, 2020 at 08:29:44PM +0300, Dmitry Osipenko wrote:
>>> 13.09.2020 19:56, Dmitry Torokhov пишет:
>>>> Hi Jiada,
>>>> On Sat, Sep 12, 2020 at 09:55:21AM +0900, Jiada Wang wrote:
>>>>> From: Nick Dyer <>
>>>>> Some maXTouch chips (eg mXT1386) will not respond on the first I2C request
>>>>> when they are in a sleep state. It must be retried after a delay for the
>>>>> chip to wake up.
>>>> Do we know when the chip is in sleep state? Can we do a quick I2C
>>>> transaction in this case instead of adding retry logic to everything? Or
>>>> there is another benefit for having such retry logic?
>>> Hello!
>>> Please take a look at page 29 of:
>>> It says that the retry is needed after waking up from a deep-sleep mode.
>>> There are at least two examples when it's needed:
>>> 1. Driver probe. Controller could be in a deep-sleep mode at the probe
>>> time, and then first __mxt_read_reg() returns I2C NACK on reading out TS
>>> hardware info.
>>> 2. Touchscreen input device is opened. The touchscreen is in a
>>> deep-sleep mode at the time when input device is opened, hence first
>>> __mxt_write_reg() invoked from mxt_start() returns I2C NACK.
>>> I think placing the retries within __mxt_read() / write_reg() should be
>>> the most universal option.
>>> Perhaps it should be possible to add mxt_wake() that will read out some
>>> generic register
>> I do not think we need to read a particular register, just doing a quick
>> read:
>> i2c_smbus_xfer(client->adapter, client->addr,
>> 0, I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &dummy)
>> should suffice.
>>> and then this helper should be invoked after HW
>>> resetting (before mxt_read_info_block()) and from mxt_start() (before
>>> mxt_set_t7_power_cfg()). But this approach feels a bit fragile to me.
>> Actually, reading the spec, it all depends on how the WAKE pin is wired
>> up on a given board. In certain setups retrying transaction is the right
>> approach, while in others explicit control is needed. So indeed, we need
>> a "wake" helper that we should call in probe and resume paths.

The WAKE-GPIO was never supported and I'm not sure whether anyone
actually needs it. I think we could ignore this case until anyone would
really need and could test it.

> By the way, I would like to avoid the unnecessary retries in probe paths
> if possible. I.e. on Chrome OS we really keep an eye on boot times and
> in case of multi-sourced touchscreens we may legitimately not have
> device at given address.

We could add a new MXT1386 DT compatible and then do:

static void mxt_wake(struct mxt_data *data)
struct i2c_client *client = data->client;
struct device *dev = &data->client->dev;
union i2c_smbus_data dummy;

if (!of_device_is_compatible(dev, "atmel,mXT1386"))

/* TODO: add WAKE-GPIO support */

i2c_smbus_xfer(client->adapter, client->addr,


Jiada, will you be able to re-work this patch? Please note that the new
"atmel,mXT1386" DT compatible needs to be added into the
atmel,maxtouch.txt binding.

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