pinctrl: mediatek: paris: Fix PIN_CONFIG_INPUT_SCHMITT_ENABLE readback

In the generic pin config library, readback of some options are handled
differently compared to the setting of those options: the argument value
is used to convey enable/disable of an option in the set path, but
success or -EINVAL is used to convey if an option is enabled or disabled
in the debugfs readback path.

PIN_CONFIG_INPUT_SCHMITT_ENABLE is one such option. Fix the readback of
the option in the mediatek-paris library, so that the debugfs dump is
not showing "input schmitt enabled" for pins that don't have it enabled.

Fixes: 1bea6afb ("pinctrl: mediatek: Refine mtk_pinconf_get()")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Message-ID: <20240327091336.3434141-2-wenst@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/mediatek/pinctrl-paris.c

@@ -193,6 +193,8 @@ static int mtk_pinconf_get(struct pinctrl_dev *pctldev,
 		}
 
 		err = mtk_hw_get_value(hw, desc, PINCTRL_PIN_REG_SMT, &ret);
+		if (!ret)
+			err = -EINVAL;
 		break;
 	case PIN_CONFIG_DRIVE_STRENGTH:
 		if (!hw->soc->drive_get)