pinctrl: at91-pio4: add support for slew-rate

SAMA7G5 supports slew rate configuration. Adapt the driver for this.
For output switching frequencies lower than 50MHz the slew rate needs to
be enabled. Since most of the pins on SAMA7G5 fall into this category
enabled the slew rate by default.

Signed-off-by: Claudiu Beznea <[e-mail]>
Acked-by: Ludovic Desroches <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-at91-pio4.c

···
 #define		ATMEL_PIO_DIR_MASK		BIT(8)
 #define		ATMEL_PIO_PUEN_MASK		BIT(9)
 #define		ATMEL_PIO_PDEN_MASK		BIT(10)
+#define		ATMEL_PIO_SR_MASK		BIT(11)
 #define		ATMEL_PIO_IFEN_MASK		BIT(12)
 #define		ATMEL_PIO_IFSCEN_MASK		BIT(13)
 #define		ATMEL_PIO_OPD_MASK		BIT(14)
···
  * @nbanks: number of PIO banks
  * @last_bank_count: number of lines in the last bank (can be less than
  *	the rest of the banks).
+ * @slew_rate_support: slew rate support
  */
 struct atmel_pioctrl_data {
 	unsigned nbanks;
 	unsigned last_bank_count;
+	unsigned int slew_rate_support;
 };
 
 struct atmel_group {
···
  * @pm_suspend_backup: backup/restore register values on suspend/resume
  * @dev: device entry for the Atmel PIO controller.
  * @node: node of the Atmel PIO controller.
+ * @slew_rate_support: slew rate support
  */
 struct atmel_pioctrl {
 	void __iomem		*reg_base;
···
 	} *pm_suspend_backup;
 	struct device		*dev;
 	struct device_node	*node;
+	unsigned int		slew_rate_support;
 };
 
 static const char * const atmel_functions[] = {
···
 			return -EINVAL;
 		arg = 1;
 		break;
+	case PIN_CONFIG_SLEW_RATE:
+		if (!atmel_pioctrl->slew_rate_support)
+			return -EOPNOTSUPP;
+		if (!(res & ATMEL_PIO_SR_MASK))
+			return -EINVAL;
+		arg = 1;
+		break;
 	case ATMEL_PIN_CONFIG_DRIVE_STRENGTH:
 		if (!(res & ATMEL_PIO_DRVSTR_MASK))
 			return -EINVAL;
···
 
 		dev_dbg(pctldev->dev, "%s: pin=%u, config=0x%lx\n",
 			__func__, pin_id, configs[i]);
+
+		/* Keep slew rate enabled by default. */
+		if (atmel_pioctrl->slew_rate_support)
+			conf |= ATMEL_PIO_SR_MASK;
 
 		switch (param) {
 		case PIN_CONFIG_BIAS_DISABLE:
···
 					ATMEL_PIO_SODR);
 			}
 			break;
+		case PIN_CONFIG_SLEW_RATE:
+			if (!atmel_pioctrl->slew_rate_support)
+				break;
+			/* And remove it if explicitly requested. */
+			if (arg == 0)
+				conf &= ~ATMEL_PIO_SR_MASK;
+			break;
 		case ATMEL_PIN_CONFIG_DRIVE_STRENGTH:
 			switch (arg) {
 			case ATMEL_PIO_DRVSTR_LO:
···
 		seq_printf(s, "%s ", "open-drain");
 	if (conf & ATMEL_PIO_SCHMITT_MASK)
 		seq_printf(s, "%s ", "schmitt");
+	if (atmel_pioctrl->slew_rate_support && (conf & ATMEL_PIO_SR_MASK))
+		seq_printf(s, "%s ", "slew-rate");
 	if (conf & ATMEL_PIO_DRVSTR_MASK) {
 		switch ((conf & ATMEL_PIO_DRVSTR_MASK) >> ATMEL_PIO_DRVSTR_OFFSET) {
 		case ATMEL_PIO_DRVSTR_ME:
···
 static const struct atmel_pioctrl_data microchip_sama7g5_pioctrl_data = {
 	.nbanks			= 5,
 	.last_bank_count	= 8, /* sama7g5 has only PE0 to PE7 */
+	.slew_rate_support	= 1,
 };
 
 static const struct of_device_id atmel_pctrl_of_match[] = {
···
 		atmel_pioctrl->npins -= ATMEL_PIO_NPINS_PER_BANK;
 		atmel_pioctrl->npins += atmel_pioctrl_data->last_bank_count;
 	}
+	atmel_pioctrl->slew_rate_support = atmel_pioctrl_data->slew_rate_support;
 
 	atmel_pioctrl->reg_base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(atmel_pioctrl->reg_base))