Re: [PATCH 1/1] Input: atmel_mxt_ts - implement I2C retries

[Wang, Jiada]

Hi Dmitry

On 2020/08/28 17:19, Dmitry Osipenko wrote:
> 21.08.2020 11:22, Jiada Wang пишет:
> > 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.
> >
> > Signed-off-by: Nick Dyer <nick.dyer@xxxxxxxxxxx>
> > Acked-by: Yufeng Shen <miletus@xxxxxxxxxxxx>
> > (cherry picked from ndyer/linux/for-upstream commit 63fd7a2cd03c3a572a5db39c52f4856819e1835d)
> > [gdavis: Forward port and fix conflicts.]
> > Signed-off-by: George G. Davis <george_davis@xxxxxxxxxx>
> > Signed-off-by: Jiada Wang <jiada_wang@xxxxxxxxxx>
> > ---
> >   drivers/input/touchscreen/atmel_mxt_ts.c | 45 ++++++++++++++++--------
> >   1 file changed, 30 insertions(+), 15 deletions(-)
>
> Hello, Jiada!
>
> I tested this patch on Acer A500 that has mXT1386 controller which
> requires the I2C retrying and everything working good, no problems
> spotted! Touchscreen doesn't work without this patch!
>
> Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx>
>
> I have one minor comment, please see it below!
>
> > diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> > index a2189739e30f..e93eda1f3d59 100644
> > --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> > +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> > @@ -196,6 +196,7 @@ enum t100_type {
> >   #define MXT_CRC_TIMEOUT		1000	/* msec */
> >   #define MXT_FW_RESET_TIME	3000	/* msec */
> >   #define MXT_FW_CHG_TIMEOUT	300	/* msec */
> > +#define MXT_WAKEUP_TIME		25	/* msec */
> >   
> >   /* Command to unlock bootloader */
> >   #define MXT_UNLOCK_CMD_MSB	0xaa
> > @@ -626,6 +627,7 @@ static int __mxt_read_reg(struct i2c_client *client,
> >   	struct i2c_msg xfer[2];
> >   	u8 buf[2];
> >   	int ret;
> > +	bool retry = false;
> >   
> >   	buf[0] = reg & 0xff;
> >   	buf[1] = (reg >> 8) & 0xff;
> > @@ -642,17 +644,22 @@ static int __mxt_read_reg(struct i2c_client *client,
> >   	xfer[1].len = len;
> >   	xfer[1].buf = val;
> >   
> > -	ret = i2c_transfer(client->adapter, xfer, 2);
> > -	if (ret == 2) {
> > -		ret = 0;
> > -	} else {
> > -		if (ret >= 0)
> > -			ret = -EIO;
> > -		dev_err(&client->dev, "%s: i2c transfer failed (%d)\n",
> > -			__func__, ret);
> > +retry_read:
> > +	ret = i2c_transfer(client->adapter, xfer, ARRAY_SIZE(xfer));
> > +	if (ret != ARRAY_SIZE(xfer)) {
>
> Is it really possible to get a positive ret != 2 from i2c_transfer()?
>
> Maybe it's better to keep the old code behaviour by returning the "ret"
> value directly if it's not equal to ARRAY_SIZE(xfer)?
I think, theoretically i2c_transfer() may return positive value but != 
number to transfer,
original behavior is,
when ret >= 0, it returns -EIO, when ret < 0, it just returns ret,

current behavior is, when ret != 2, it returns -EIO, after retry.

I am OK to change the behavior exactly as same original one.

Thanks,
Jiada