pinctrl: sunxi: Support I/O bias voltage setting on H6

H6 SoC has a "pio group withstand voltage mode" register (datasheet
description), that needs to be used to select either 1.8V or 3.3V I/O mode,
based on what voltage is powering the respective pin banks and is thus used
for I/O signals.

Add support for configuring this register according to the voltage of the
pin bank regulator (if enabled).

This is similar to the support for I/O bias voltage setting patch for A80
and the same concerns apply. See:

commit 402bfb3c1352 ("Support I/O bias voltage setting on A80")

Signed-off-by: Ondrej Jirman <[e-mail]>
Acked-by: Maxime Ripard <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/sunxi/pinctrl-sun50i-h6.c

···
 	.irq_banks = 4,
 	.irq_bank_map = h6_irq_bank_map,
 	.irq_read_needs_mux = true,
+	.io_bias_cfg_variant = BIAS_VOLTAGE_PIO_POW_MODE_SEL,
 };
 
 static int h6_pinctrl_probe(struct platform_device *pdev)

drivers/pinctrl/sunxi/pinctrl-sunxi.c

···
 					 unsigned pin,
 					 struct regulator *supply)
 {
+	unsigned short bank = pin / PINS_PER_BANK;
+	unsigned long flags;
 	u32 val, reg;
 	int uV;
 
···
 		reg = readl(pctl->membase + sunxi_grp_config_reg(pin));
 		reg &= ~IO_BIAS_MASK;
 		writel(reg | val, pctl->membase + sunxi_grp_config_reg(pin));
+		return 0;
+	case BIAS_VOLTAGE_PIO_POW_MODE_SEL:
+		val = uV <= 1800000 ? 1 : 0;
+
+		raw_spin_lock_irqsave(&pctl->lock, flags);
+		reg = readl(pctl->membase + PIO_POW_MOD_SEL_REG);
+		reg &= ~(1 << bank);
+		writel(reg | val << bank, pctl->membase + PIO_POW_MOD_SEL_REG);
+		raw_spin_unlock_irqrestore(&pctl->lock, flags);
 		return 0;
 	default:
 		return -EINVAL;

drivers/pinctrl/sunxi/pinctrl-sunxi.h

···
 #define PINCTRL_SUN7I_A20	BIT(7)
 #define PINCTRL_SUN8I_R40	BIT(8)
 
+#define PIO_POW_MOD_SEL_REG	0x340
+
 enum sunxi_desc_bias_voltage {
 	BIAS_VOLTAGE_NONE,
 	/*
···
 	 * Pn_GRP_CONFIG registers, as seen on A80 SoC.
 	 */
 	BIAS_VOLTAGE_GRP_CONFIG,
+	/*
+	 * Bias voltage is set through PIO_POW_MOD_SEL_REG
+	 * register, as seen on H6 SoC, for example.
+	 */
+	BIAS_VOLTAGE_PIO_POW_MODE_SEL,
 };
 
 struct sunxi_desc_function {