Re: [PATCH v2 1/2] Input: mms114 - use smbus functions whenever possible

[Stephan Gerhold <stephan@gerhold.net>]

Hi Andi,

Thanks for working on these patches!

Not sure if you saw my comment regarding your patch [1],
so I'll just repeat it properly inline here:

[1]: https://patchwork.kernel.org/patch/11178515/#22927311

On Sun, Oct 20, 2019 at 11:28:55PM +0300, Andi Shyti wrote:
> The exchange of data to and from the mms114 touchscreen never
> exceeds 256 bytes. In the worst case it goes up to 80 bytes in
> the interrupt handler while reading the events.
> 

i2c_smbus_read_i2c_block_data() is actually limited to
I2C_SMBUS_BLOCK_MAX = 32.

> Thus it's not needed to make use of custom read/write functions
> for accessing the i2c. Replace, whenever possible, the use of
> custom functions with the more standard smbus ones.
> 
> It's not possible only in one case, in the mms114_set_active()
> function where the 'cache_mode_control' variable is updated
> according to the value in the register 'MMS114_MODE_CONTROL'
> register.
> 
> Signed-off-by: Andi Shyti <andi@etezian.org>
> Tested-by: Seung-Woo Kim <sw0312.kim@samsung.com>
> ---
>  drivers/input/touchscreen/mms114.c | 32 +++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/mms114.c b/drivers/input/touchscreen/mms114.c
> index a5ab774da4cc..170dcb5312b9 100644
> --- a/drivers/input/touchscreen/mms114.c
> +++ b/drivers/input/touchscreen/mms114.c
> @@ -204,14 +204,15 @@ static irqreturn_t mms114_interrupt(int irq, void *dev_id)
>  	}
>  	mutex_unlock(&input_dev->mutex);
>  
> -	packet_size = mms114_read_reg(data, MMS114_PACKET_SIZE);
> +	packet_size = i2c_smbus_read_byte_data(data->client,
> +					       MMS114_PACKET_SIZE);
>  	if (packet_size <= 0)
>  		goto out;
>  
>  	touch_size = packet_size / MMS114_PACKET_NUM;
>  
> -	error = __mms114_read_reg(data, MMS114_INFORMATION, packet_size,
> -			(u8 *)touch);
> +	error = i2c_smbus_read_i2c_block_data(data->client, MMS114_INFORMATION,
> +					      packet_size, (u8 *)touch);

... and here we try to read up to 80 bytes, as you mentioned.

i2c_smbus_read_i2c_block_data() will silently fall back to reading only
32 bytes. Therefore, if we try to read more than 32 bytes here we will
later read uninitialized data.

With this change, if you use more than 4 fingers you can easily trigger
a situation where one of the fingers gets "stuck", together with:
  mms114 4-0048: Wrong touch type (0)

So we still need the custom functions here, or maybe avoid the problem
by using regmap instead.

>  	if (error < 0)
>  		goto out;
>  
> @@ -251,7 +252,8 @@ static int mms114_get_version(struct mms114_data *data)
>  
>  	switch (data->type) {
>  	case TYPE_MMS152:
> -		error = __mms114_read_reg(data, MMS152_FW_REV, 3, buf);
> +		error = i2c_smbus_read_i2c_block_data(data->client,
> +						      MMS152_FW_REV, 3, buf);
>  		if (error)

i2c_smbus_read_i2c_block_data() returns the number of read bytes,
therefore this check will always fail.

It should be: if (error < 0)

>  			return error;
>  
> @@ -265,7 +267,8 @@ static int mms114_get_version(struct mms114_data *data)
>  		break;
>  
>  	case TYPE_MMS114:
> -		error = __mms114_read_reg(data, MMS114_TSP_REV, 6, buf);
> +		error = i2c_smbus_read_i2c_block_data(data->client,
> +						      MMS114_TSP_REV, 6, buf);
>  		if (error)

As above.

>  			return error;
>  
> @@ -297,30 +300,35 @@ static int mms114_setup_regs(struct mms114_data *data)
>  
>  	val = (props->max_x >> 8) & 0xf;
>  	val |= ((props->max_y >> 8) & 0xf) << 4;
> -	error = mms114_write_reg(data, MMS114_XY_RESOLUTION_H, val);
> +	error = i2c_smbus_write_byte_data(data->client,
> +					  MMS114_XY_RESOLUTION_H, val);
>  	if (error < 0)
>  		return error;
>  
>  	val = props->max_x & 0xff;
> -	error = mms114_write_reg(data, MMS114_X_RESOLUTION, val);
> +	error = i2c_smbus_write_byte_data(data->client,
> +					  MMS114_X_RESOLUTION, val);
>  	if (error < 0)
>  		return error;
>  
>  	val = props->max_x & 0xff;
> -	error = mms114_write_reg(data, MMS114_Y_RESOLUTION, val);
> +	error = i2c_smbus_write_byte_data(data->client,
> +					  MMS114_Y_RESOLUTION, val);
>  	if (error < 0)
>  		return error;
>  
>  	if (data->contact_threshold) {
> -		error = mms114_write_reg(data, MMS114_CONTACT_THRESHOLD,
> -				data->contact_threshold);
> +		error = i2c_smbus_write_byte_data(data->client,
> +						  MMS114_CONTACT_THRESHOLD,
> +						  data->contact_threshold);
>  		if (error < 0)
>  			return error;
>  	}
>  
>  	if (data->moving_threshold) {
> -		error = mms114_write_reg(data, MMS114_MOVING_THRESHOLD,
> -				data->moving_threshold);
> +		error = i2c_smbus_write_byte_data(data->client,
> +						  MMS114_MOVING_THRESHOLD,
> +						  data->moving_threshold);
>  		if (error < 0)
>  			return error;
>  	}
> -- 
> 2.24.0.rc0
>