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 <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. 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, 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.
