Re: [PATCH] Input: touchscreen: tsc2007: Reduce I2C transactions for Z2 read

[Andreas Kemnade <andreas@kemnade.info>]

Hi,

On Sun, 19 Apr 2026 17:18:23 -0700
Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:

> Hi Yuki,
> 
> On Fri, Apr 10, 2026 at 04:41:00PM +0900, Yuki Horii wrote:
> > From: Yuki Horii <yuuki198708@gmail.com>
> > 
> > The current implementation sends a separate power-down command
> > after reading the Z2 value, resulting in an extra I2C
> > transaction per measurement cycle.
> > 
> > The TSC2007 command byte contains a 2-bit power-down mode
> > selection field. By selecting the power-down state in the Z2
> > measurement command, the device powers down after the Z2 A/D
> > conversion completes, eliminating the subsequent power-down
> > transaction.
> > 
> > This reduces the number of I2C transactions by one per touch
> > measurement cycle, decreasing I2C bus overhead and improving
> > touch sampling performance.
> > 
> > Signed-off-by: Yuki Horii <yuuki198708@gmail.com>
> > ---
> >  drivers/input/touchscreen/tsc2007_core.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/input/touchscreen/tsc2007_core.c b/drivers/input/touchscreen/tsc2007_core.c
> > index 948935de894b..ff60245baa96 100644
> > --- a/drivers/input/touchscreen/tsc2007_core.c
> > +++ b/drivers/input/touchscreen/tsc2007_core.c
> > @@ -61,10 +61,8 @@ static void tsc2007_read_values(struct tsc2007 *tsc, struct ts_event *tc)
> >  
> >  	/* turn y+ off, x- on; we'll use formula #1 */
> >  	tc->z1 = tsc2007_xfer(tsc, READ_Z1);
> > -	tc->z2 = tsc2007_xfer(tsc, READ_Z2);
> > -
> > -	/* Prepare for next touch reading - power down ADC, enable PENIRQ */
> > -	tsc2007_xfer(tsc, PWRDOWN);
> > +	/* Read Z2 and power down ADC after A/D conversion, enable PENIRQ */
> > +	tc->z2 = tsc2007_xfer(tsc, (TSC2007_POWER_OFF_IRQ_EN | TSC2007_MEASURE_Z2));
> >  }
> >  
> >  u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)  
> 
> Thank you for the patch.
> 
> I'd like people using this part to chime in (CCed).
> 
This looks like that there might be some reason behind it. But I cannot find any.
Either by reading the datasheet nor by testing.

I have checked the interrupt counter. Output seems still be same.
Interrupts appear when finger is moving.

So 
Tested-by: Andreas Kemnade <andreas@kemnade.info> # GTA04



> Thanks.
>