power: reset: at91-reset: handle nrst async for sam9x60

Handle NRST asynchronously for SAM9X60 to avoid problem with fast drop of
VDDCORE on shutdown operations in the first 100 us after CPU is shutdown.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/reset/at91-reset.c

@@ -35,6 +35,7 @@
 
 #define AT91_RSTC_MR	0x08		/* Reset Controller Mode Register */
 #define AT91_RSTC_URSTEN	BIT(0)		/* User Reset Enable */
+#define AT91_RSTC_URSTASYNC	BIT(2)		/* User Reset Asynchronous Control */
 #define AT91_RSTC_URSTIEN	BIT(4)		/* User Reset Interrupt Enable */
 #define AT91_RSTC_ERSTL		GENMASK(11, 8)	/* External Reset Length */
 
@@ -228,6 +229,13 @@ static int __init at91_reset_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, reset);
 
+	if (of_device_is_compatible(pdev->dev.of_node, "microchip,sam9x60-rstc")) {
+		u32 val = readl(reset->rstc_base + AT91_RSTC_MR);
+
+		writel(AT91_RSTC_KEY | AT91_RSTC_URSTASYNC | val,
+		       reset->rstc_base + AT91_RSTC_MR);
+	}
+
 	ret = register_restart_handler(&reset->nb);
 	if (ret) {
 		clk_disable_unprepare(reset->sclk);