pinctrl: renesas: Add support for R-Car SoCs with pull-down only pins

Currently, the common R-Car bias handling supports pin controllers with
either:
1. Separate pin Pull-Enable (PUEN) and pin Pull-Up/Down control (PUD)
registers, for controlling both pin pull-up and pin pull-down,
2. A single pin Pull-Up control register (PUPR), for controlling pin
pull-up.

Add support for a variant of #2, where some bits in the single pin
Pull-Up control register (PUPR) control pin pull-down instead of pin
pull-up. This is the case for the "ASEBRK#/ACK" pin on R-Car M2-W,
M2-N, and E2, and the "ACK" pin on RZ/G1M, RZ/G1N, RZ/G1E, and RZ/G1C.
To describe such a register, SoC-specific drivers need to provide two
instances of pinmux_bias_reg: a first one with the puen field filled in,
listing pins with pull-up functionality, and a second one with the pud
field filled in, listing pins with pull-down functionality.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Niklas Söderlund <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/pinctrl/renesas/pinctrl.c

···
 {
 	unsigned int i, j;
 
-	for (i = 0; pfc->info->bias_regs[i].puen; i++) {
+	for (i = 0; pfc->info->bias_regs[i].puen || pfc->info->bias_regs[i].pud; i++) {
 		for (j = 0; j < ARRAY_SIZE(pfc->info->bias_regs[i].pins); j++) {
 			if (pfc->info->bias_regs[i].pins[j] == pin) {
 				*bit = j;
···
 	if (!reg)
 		return PIN_CONFIG_BIAS_DISABLE;
 
-	if (!(sh_pfc_read(pfc, reg->puen) & BIT(bit)))
-		return PIN_CONFIG_BIAS_DISABLE;
-	else if (!reg->pud || (sh_pfc_read(pfc, reg->pud) & BIT(bit)))
-		return PIN_CONFIG_BIAS_PULL_UP;
-	else
-		return PIN_CONFIG_BIAS_PULL_DOWN;
+	if (reg->puen) {
+		if (!(sh_pfc_read(pfc, reg->puen) & BIT(bit)))
+			return PIN_CONFIG_BIAS_DISABLE;
+		else if (!reg->pud || (sh_pfc_read(pfc, reg->pud) & BIT(bit)))
+			return PIN_CONFIG_BIAS_PULL_UP;
+		else
+			return PIN_CONFIG_BIAS_PULL_DOWN;
+	} else {
+		if (sh_pfc_read(pfc, reg->pud) & BIT(bit))
+			return PIN_CONFIG_BIAS_PULL_DOWN;
+		else
+			return PIN_CONFIG_BIAS_DISABLE;
+	}
 }
 
 void rcar_pinmux_set_bias(struct sh_pfc *pfc, unsigned int pin,
···
 	if (!reg)
 		return;
 
-	enable = sh_pfc_read(pfc, reg->puen) & ~BIT(bit);
-	if (bias != PIN_CONFIG_BIAS_DISABLE)
-		enable |= BIT(bit);
+	if (reg->puen) {
+		enable = sh_pfc_read(pfc, reg->puen) & ~BIT(bit);
+		if (bias != PIN_CONFIG_BIAS_DISABLE)
+			enable |= BIT(bit);
 
-	if (reg->pud) {
-		updown = sh_pfc_read(pfc, reg->pud) & ~BIT(bit);
-		if (bias == PIN_CONFIG_BIAS_PULL_UP)
-			updown |= BIT(bit);
+		if (reg->pud) {
+			updown = sh_pfc_read(pfc, reg->pud) & ~BIT(bit);
+			if (bias == PIN_CONFIG_BIAS_PULL_UP)
+				updown |= BIT(bit);
 
-		sh_pfc_write(pfc, reg->pud, updown);
+			sh_pfc_write(pfc, reg->pud, updown);
+		}
+
+		sh_pfc_write(pfc, reg->puen, enable);
+	} else {
+		enable = sh_pfc_read(pfc, reg->pud) & ~BIT(bit);
+		if (bias == PIN_CONFIG_BIAS_PULL_DOWN)
+			enable |= BIT(bit);
+
+		sh_pfc_write(pfc, reg->pud, enable);
 	}
-
-	sh_pfc_write(pfc, reg->puen, enable);
 }
 
 #define PORTnCR_PULMD_OFF	(0 << 6)

drivers/pinctrl/renesas/sh_pfc.h

···
 	.reg = r, \
 	.fields =
 
-struct pinmux_bias_reg {
+struct pinmux_bias_reg {	/* At least one of puen/pud must exist */
 	u32 puen;		/* Pull-enable or pull-up control register */
-	u32 pud;		/* Pull-up/down control register (optional) */
+	u32 pud;		/* Pull-up/down or pull-down control register */
 	const u16 pins[32];
 };