On Tue, Sep 15, 2020 at 12:33:18AM +0300, 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 <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. 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. > > > 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? Thanks. -- Dmitry
