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Subject: Re: [PATCH 1/1] Input: atmel_mxt_ts - implement I2C retries
To:     Jiada Wang <jiada_wang@mentor.com>, nick@shmanahar.org,
        dmitry.torokhov@gmail.com
Cc:     linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
        erosca@de.adit-jv.com, Andrew_Gabbasov@mentor.com
References: <20200821082254.16661-1-jiada_wang@mentor.com>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <64c77ff9-6d20-abcf-f549-7d5c85fba28d@gmail.com>
Date:   Fri, 28 Aug 2020 11:19:49 +0300
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21.08.2020 11:22, Jiada Wang пишет:
> From: Nick Dyer <nick.dyer@itdev.co.uk>
> 
> 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@itdev.co.uk>
> Acked-by: Yufeng Shen <miletus@chromium.org>
> (cherry picked from ndyer/linux/for-upstream commit 63fd7a2cd03c3a572a5db39c52f4856819e1835d)
> [gdavis: Forward port and fix conflicts.]
> Signed-off-by: George G. Davis <george_davis@mentor.com>
> Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
> ---
>  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@gmail.com>

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)?