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 <nick.dyer@xxxxxxxxxxx> >> >> 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 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. AFAIK, there shouldn't be any extra benefits from the retrying other than to handle the deep-sleep of mxt1386.
