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 <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 > > 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. 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. Thanks. -- Dmitry
