Troubleshooting • Re: How to apply calibration matrix for touch screen based on ADS7846?

After looking at:
https://github.com/raspberrypi/linux/bl ... verlay.dts
https://github.com/raspberrypi/linux/bl ... verlay.dts

I see that there are no parameters:
touchscreen-size-x = <320>;
touchscreen-size-y = <480>;
touchscreen-x-mm = <49>;
touchscreen-y-mm = <74>;

But there are similar parameters in mipi-dbi-spi-overlay.dts:
width-mm = <&panel>, "width-mm:0";
height-mm = <&panel>, "height-mm:0";

And in ads7846-overlay.dts:
xmin = <&ads7846>,"ti,x-min;0";
ymin = <&ads7846>,"ti,y-min;0";
xmax = <&ads7846>,"ti,x-max;0";
ymax = <&ads7846>,"ti,y-max;0";

Do you have experience changing those xmin, xmax, ymin, ymax, with the numbers reported by "libinput measure"?
I didn't try it yet because it feels like a circular fallacy to calibrate the touch screen this way.

More references:
https://www.kernel.org/doc/Documentatio ... i-spi.yaml
https://www.kernel.org/doc/Documentatio ... ds7846.txt

^ Oh, I see. The parameters touchscree-size-x, y, x-mm, y-mm are part of the kernel driver optional parameters, but not available through the raspberry-provided DTS.

Digging deeper:
https://www.kernel.org/doc/Documentatio ... creen.yaml

Statistics: Posted by robertojguerra — Wed Jul 16, 2025 5:38 pm

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