tty: serial: samsung_tty: Add earlycon support for Apple UARTs

Earlycon support is identical to S3C2410, but Apple SoCs also need
MMIO mapped as nGnRnE. This is handled generically for normal drivers
including the normal UART path here, but earlycon uses fixmap and
runs before that scaffolding is ready.

Since this is the only case where we need this fix, it makes more
sense to do it here in the UART driver instead of introducing a
whole fdt nonposted-mmio resolver just for earlycon/fixmap.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210304213902.83903-26-marcan@marcan.st
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/samsung_tty.c

@@ -3001,6 +3001,23 @@ OF_EARLYCON_DECLARE(s5pv210, "samsung,s5pv210-uart",
 			s5pv210_early_console_setup);
 OF_EARLYCON_DECLARE(exynos4210, "samsung,exynos4210-uart",
 			s5pv210_early_console_setup);
+
+/* Apple S5L */
+static int __init apple_s5l_early_console_setup(struct earlycon_device *device,
+						const char *opt)
+{
+	/* Close enough to S3C2410 for earlycon... */
+	device->port.private_data = &s3c2410_early_console_data;
+
+#ifdef CONFIG_ARM64
+	/* ... but we need to override the existing fixmap entry as nGnRnE */
+	__set_fixmap(FIX_EARLYCON_MEM_BASE, device->port.mapbase,
+		     __pgprot(PROT_DEVICE_nGnRnE));
+#endif
+	return samsung_early_console_setup(device, opt);
+}
+
+OF_EARLYCON_DECLARE(s5l, "apple,s5l-uart", apple_s5l_early_console_setup);
 #endif
 
 MODULE_ALIAS("platform:samsung-uart");