pinctrl: bcm2835: Implement bcm2835_pinconf_get

Even the driver already has implemented pin_dbg_show, it could
be helpful to implement pin_conf_get for a more generic behavior.
Contrary to the BCM2711, the BCM2835 SOC doesn't allow to read
the bias config, so the implementation is limited to the basics.

Keep ENOTSUPP here, because it's only used internally.
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Message-ID: <20240307070113.4888-2-wahrenst@gmx.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/bcm/pinctrl-bcm2835.c

@@ -1003,8 +1003,27 @@ static const struct pinmux_ops bcm2835_pmx_ops = {
 static int bcm2835_pinconf_get(struct pinctrl_dev *pctldev,
 			unsigned pin, unsigned long *config)
 {
-	/* No way to read back config in HW */
+	enum pin_config_param param = pinconf_to_config_param(*config);
+	struct bcm2835_pinctrl *pc = pinctrl_dev_get_drvdata(pctldev);
+	enum bcm2835_fsel fsel = bcm2835_pinctrl_fsel_get(pc, pin);
+	u32 val;
+
+	/* No way to read back bias config in HW */
+
+	switch (param) {
+	case PIN_CONFIG_OUTPUT:
+		if (fsel != BCM2835_FSEL_GPIO_OUT)
+			return -EINVAL;
+
+		val = bcm2835_gpio_get_bit(pc, GPLEV0, pin);
+		*config = pinconf_to_config_packed(param, val);
+		break;
+
+	default:
 		return -ENOTSUPP;
+	}
+
+	return 0;
 }
 
 static void bcm2835_pull_config_set(struct bcm2835_pinctrl *pc,