Re: [PATCH v2 2/2] Input: atmel_mxt_ts - wake mXT1386 from deep-sleep mode

From: Wang, Jiada
Date: Sun Sep 20 2020 - 10:46:42 EST

Hi Dmitry

On 2020/09/20 23:21, Dmitry Osipenko wrote:
20.09.2020 16:13, Wang, Jiada пишет:
Hi Dmitry

On 2020/09/20 15:02, Dmitry Torokhov wrote:
On Sat, Sep 19, 2020 at 10:28 PM Wang, Jiada <jiada_wang@xxxxxxxxxx>

Hi Dmitry

On 2020/09/20 4:49, Dmitry Osipenko wrote:
18.09.2020 18:55, Wang, Jiada пишет:
    +static void mxt_wake(struct mxt_data *data)
+    struct i2c_client *client = data->client;
+    struct device *dev = &data->client->dev;
+    struct device_node *np = dev->of_node;
+    union i2c_smbus_data dummy;
+    if (!of_device_is_compatible(np, "atmel,mXT1386"))
+        return;
I'm not sure whether you misses the previous answers from Dmitry
Torokhov and Rob Herring, but they suggested to add a new device-tree
property which should specify the atmel,wakeup-method.

I think Rob Herring prefers for the compatible solution than property.

Actually, seems you're right. But I'm not sure now whether he just made
a typo, because it's actually a board-specific option.

Right, I think since it is a board specific issue,
so "property" is the preferred way,

Why are you saying it is a board-specific issue? It seems to me that
it is behavior of a given controller, not behavior of a board that
happens to use such a controller?

the issue only occurs on mXT1386 controller,
but with same mXT1386 soc, behavior differs from how WAKE line is
connected, (left low, connect to GPIO or connect to SCL),
so I think the issue also is board-specific?

if I understand you correctly,
compatible combine with property is what you are suggesting, right?

We should gate the behavior either off a compatible or a new property,
but not both.

Both variants will work. But if other controller models have a similar
need, then a wakeup-method property should be more universal since
potentially it could be reused by other TS models without much changes
to the code.

To be honest, I'm not familiar with other Atmel TS controllers, so have
no clue what variant should be more preferred. The wakeup-method should
be a safer variant, but it also will be a bit more invasive code change.

It could be more preferred to skip the i2c_smbus_xfer() for the NONE
variant, but it also should be harmless in practice. I guess we indeed
could keep the current variant of yours patch and then add a clarifying
comment to the commit message and to the code, telling that
i2c_smbus_xfer() is harmless in a case of the hardwired WAKE-LINE.

I will skip dummy read for "NONE" variant.

There are 3 possible variants:

     - NONE
     - GPIO
     - I2C-SCL

Hence we should bail out from mxt_wake() if method is set to NONE or

for "GPIO", we still need 25 ms sleep. but rather than a dummy read,
WAKE line need to be asserted before sleep.

Correct, I just meant to bail out because GPIO is currently


    static int mxt_initialize(struct mxt_data *data)
        struct i2c_client *client = data->client;
        int recovery_attempts = 0;
        int error;
    +    mxt_wake(data);
        while (1) {

I assume the mxt_wake() should be placed here, since there is a 3
seconds timeout in the end of the while-loop, meaning that device may
get back into deep-sleep on a retry.

Can you elaborate a little more why exit from bootload mode after
for 3 second could enter deep-sleep mode.

The loop attempts to exit from bootload mode and then I suppose
mxt_read_info_block() may fail if I2C "accidentally" fails, hence the
deep-sleep mode still will be enabled on a retry.

If the controller is in bootloader mode it will not be in a deep sleep
mode. If the controller was just reset via reset GPIO it will not be
in deep sleep mode. The controller can only be in deep sleep mode if
someone requested deep sleep mode. I'd recommend moving the mxt_wake
in the "else" case of handling reset GPIO.

My observation on Acer A500 shows that first I2C transfer after the
reset via GPIO could easily get a NAK, hence mxt_wake() definitely must
be placed before the mxt_read_info_block(). Apparently reset doesn't
wake controller.

What's even more interesting is that I now spotted that the NAK could
happen in mxt_interrupt() after mxt_initialize().

I'm also now seeing that both mxt_set_t7_power_cfg() and
mxt_t6_command() in mxt_start() need the mxt_wake()! Because both 100%
get a NAK without the wakes.

@@ -3005,9 +3022,11 @@ static void mxt_start(struct mxt_data *data)

+ mxt_wake(data);
mxt_set_t7_power_cfg(data, MXT_POWER_CFG_RUN);

/* Recalibrate since chip has been in deep sleep */
+ mxt_wake(data);
mxt_t6_command(data, MXT_COMMAND_CALIBRATE, 1, false);

Maybe adding I2C retries still isn't a bad idea?

Yes, by working on find out where need to place mxt_wake(),
I am having feeling, we must over look somewhere which needs mxt_wake(),
also it will introduce lots of difficulty, later someone needs add some new routines.

probably based on retries idea, we can add "compatible" check,
to only narrow the retry mechanism happen on mXT1368 controller,
is more easier way...