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SubjectRe: [PATCH v4 1/1] Input: atmel_mxt_ts - implement I2C retries
Hi Dmitry

On 2020/09/15 6:33, Dmitry Osipenko wrote:
> 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"))
> return;
> /* TODO: add WAKE-GPIO support */
> i2c_smbus_xfer(client->adapter, client->addr,
> &dummy);
> msleep(MXT_WAKEUP_TIME);
> }
> 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.

Yes, I can re-work this patch, and add one more change to dts-binding.

to summarize long discussion in this thread,
I think what I need to do are:
1) since the change will be different from current one, I will need to
start a new patch
2) call mxt_wake() in mxt_probe() and mxt_resume()
3) update atmel,maxtouch.txt binding

please correct me if I am wrong.


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