Re: [PATCH 03/14] ARM: dts: imx6dl-b155v2: add touchscreen size properties

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] ARM: dts: imx6dl-b155v2: panel size in touchscreen-size-x/y breaks touch
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commit a32e64e0ae8dfc5c902cc7abdcc408b2bb7583c9
Author: Frank Li <Frank.Li@nxp.com>

ARM: dts: imx6dl-b155v2: add touchscreen size properties

This commit adds touchscreen-size-x and touchscreen-size-y properties to the
eeti,exc80h84 touchscreen node in imx6dl-b155v2.dts to satisfy the
eeti,exc3000 devicetree schema requirements.

> diff --git a/arch/arm/boot/dts/nxp/imx/imx6dl-b155v2.dts b/arch/arm/boot/dts/nxp/imx/imx6dl-b155v2.dts
> index 7edc788bcb8f3..54db44613df66 100644
> --- a/arch/arm/boot/dts/nxp/imx/imx6dl-b155v2.dts
> +++ b/arch/arm/boot/dts/nxp/imx/imx6dl-b155v2.dts
> @@ -25,6 +25,8 @@ touchscreen@2a {
>  		pinctrl-0 = <&pinctrl_q7_gpio0>;
>  		interrupt-parent = <&gpio5>;
>  		interrupts = <2 IRQ_TYPE_LEVEL_LOW>;
> +		touchscreen-size-x = <1366>;
> +		touchscreen-size-y = <768>;
>  		touchscreen-inverted-x;
>  		touchscreen-inverted-y;
>  		reset-gpios = <&tca6424a 21 GPIO_ACTIVE_HIGH>;

[Severity: High]
Does setting touchscreen-size-x and touchscreen-size-y to the display panel's
1366x768 pixel resolution introduce a regression in touch coordinate reporting
for this controller?

Per Documentation/devicetree/bindings/input/touchscreen/touchscreen.yaml,
touchscreen-size-x and touchscreen-size-y describe the coordinate space of the
touchscreen controller itself (maximum coordinate reported + 1), rather than
the LCD panel dimensions.

In drivers/input/touchscreen/exc3000.c, exc3000_info defines the native 14-bit
coordinate maximum for the EXC80H84 controller:

	[EETI_EXC80H84] = {
		.name = "EETI EXC80H84 Touch Screen",
		.max_xy = SZ_16K - 1,
	},

During probe, exc3000_probe() initializes the axes to [0, 16383], and then
calls touchscreen_parse_properties():

	max_xy = data->info->max_xy;
	input_set_abs_params(input, ABS_MT_POSITION_X, 0, max_xy, 0, 0);
	input_set_abs_params(input, ABS_MT_POSITION_Y, 0, max_xy, 0, 0);

	touchscreen_parse_properties(input, true, &data->prop);

With touchscreen-size-x = <1366> and touchscreen-size-y = <768>,
touchscreen_parse_properties() overwrites the axis maximums and
data->prop.max_x / max_y to 1365 and 767.

However, the exc3000 driver does not program these dimensions into the
hardware or scale the raw coordinates in software. When a touch interrupt
occurs, exc3000_interrupt() -> exc3000_handle_mt_event() ->
exc3000_report_slots() passes unscaled 14-bit coordinates (0..16383) directly
to touchscreen_report_pos():

	touchscreen_report_pos(input, prop,
			       get_unaligned_le16(buf + 2),
			       get_unaligned_le16(buf + 4),
			       true);

Because touchscreen-inverted-x and touchscreen-inverted-y are also set on
touchscreen@2a, touchscreen_report_pos() -> touchscreen_apply_prop_to_x_y()
inverts the raw coordinates against the overridden maximums:

	if (prop->invert_x)
		*x = prop->max_x - *x;

	if (prop->invert_y)
		*y = prop->max_y - *y;

Whenever the controller reports raw X > 1365 or raw Y > 767, this unsigned
subtraction wraps around and reports negative coordinates to input_report_abs(),
while also advertising the wrong axis range to userspace.

Should touchscreen-size-x and touchscreen-size-y be set to <16384> to match
the EETI EXC80H84 controller's 16384x16384 coordinate space?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261016-arm_dts_cleanup2-v1-0-3a0cab9fd784@nxp.com?part=3