Re: [RFC 1/4] Input: edt-ft5x06 - Use max support points to determine how much to read

["Franklin S Cooper Jr." <fcooper@ti.com>]

On 10/14/2015 06:39 PM, Dmitry Torokhov wrote:
> On Wed, Oct 07, 2015 at 07:21:38AM -0500, fcooper@ti.com wrote:
>> From: Franklin S Cooper Jr <fcooper@ti.com>
>>
>> Calculate the amount of data that needs to be read for the specified max
>> number of support points. If the maximum number of support points changes
>> then the amount that is read from the touch screen controller should
>> reflect this.
>>
>> Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
>> ---
>>  drivers/input/touchscreen/edt-ft5x06.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/input/touchscreen/edt-ft5x06.c b/drivers/input/touchscreen/edt-ft5x06.c
>> index 7239c31..1e0ed6e 100644
>> --- a/drivers/input/touchscreen/edt-ft5x06.c
>> +++ b/drivers/input/touchscreen/edt-ft5x06.c
>> @@ -178,14 +178,16 @@ static irqreturn_t edt_ft5x06_ts_isr(int irq, void *dev_id)
>>  		cmd = 0xf9; /* tell the controller to send touch data */
>>  		offset = 5; /* where the actual touch data starts */
>>  		tplen = 4;  /* data comes in so called frames */
>> -		datalen = 26; /* how much bytes to listen for */
>> +
>> +		/* how many bytes to listen for */
>> +		datalen = tplen * MAX_SUPPORT_POINTS + offset + 1;
>>  		break;
>>  
>>  	case M09:
>>  		cmd = 0x02;
>>  		offset = 1;
>>  		tplen = 6;
>> -		datalen = 29;
>> +		datalen = tplen * MAX_SUPPORT_POINTS - cmd + 1;
>>  		break;
>
> Hmm, why would formulae for datalen be different depending on the
> firmware? And I think original 29 it too low: we need 30 bytes for 5
> contacts + 1 to account for offset.
So based on the current ISR we don't care about the touch weight and
which are the last two registers for each touch point. So for the last
touchpoint we really don't need to read the extra two registers (-2).
We need +1 simply for the fact that we read the register at location
cmd.

So 6 * 5 - 2 + 1 which is how we get to 29. The formula looks slightly
different because the registers we are reading are very close to zero
so the math works out to equal the equation I used for M09.

M06 since tplen = 4 then all four registers are used in the ISR per touch
point. Plus the offset and plus 1 again to account for the fact we are reading
the cmd register. But once again it would be nice if someone can confirm this.
>
> I also wonder why we need extra 1 byte in M06 case.
>
> Lothar?
>
> Thanks.
>