On Mon, Sep 14, 2020 at 4:32 PM Dmitry Torokhov
[off-list ref] wrote:

On Tue, Sep 15, 2020 at 12:33:18AM +0300, Dmitry Osipenko wrote:

quoted

14.09.2020 22:36, Dmitry Torokhov пишет:

quoted

On Mon, Sep 14, 2020 at 12:33:40PM -0700, Dmitry Torokhov wrote:

quoted

On Mon, Sep 14, 2020 at 08:29:44PM +0300, Dmitry Osipenko wrote:

quoted

13.09.2020 19:56, Dmitry Torokhov пишет:

quoted

Hi Jiada,

On Sat, Sep 12, 2020 at 09:55:21AM +0900, Jiada Wang wrote:

quoted

From: Nick Dyer <redacted>

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:

https://ww1.microchip.com/downloads/en/DeviceDoc/mXT1386_1vx_Datasheet_LX.pdf

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.

quoted

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.

Right, I am not advocating adding GPIO control right away, I was simply
arguing why I believe we should separate wakeup handling from normal
communication handling.

quoted

quoted

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,
                      0, I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE,
                      &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.

Another option is to have a device property "atmel,wakeup-type" or
something, in case there are more Atmel variants needing this.

Rob, any preferences here?

If device specific, then I prefer to be implied by the compatible. If
board specific, then a property is appropriate. Seems like this is the
former case.

Rob