Help with confirming an error trace in drivers/input/touchscreen/ad7879-spi.c

Hi there,

My name is Shaobo He and I am a graduate student at University of Utah. 
I am applying a static analysis tool to the Linux device drivers and got 
an error trace of null pointer dereference in 
drivers/input/touchscreen/ad7879-spi.c staring from 
`ad7879_spi_multi_read`: it calls `ad7879_spi_xfer` with the argument 
`tx_buf` being NULL, which gets dereferenced at line 52 given the 
argument `count` being 1 
(http://lxr.free-electrons.com/source/drivers/input/touchscreen/ad7879-spi.c#L52). 
As you can see, the error trace is only plausible since it depends on 
certain conditions. To be more specific, is it possible for the count 
argument to be 1. Therefore, I was wondering if you could help me 
confirm it since you are one of the authors of this driver.

Thanks for your time. I am looking forward to your reply.

Best,
Shaobo