serial: cadence: Add generic earlycon support

Add earlycon support for the cadence serial port.
This is based on recent patches:
"tty/serial: pl011: add generic earlycon support"
(sha1: 0d3c673e7881e691991b2a4745bd4f149603baa2)
"tty/serial: add arm/arm64 semihosting earlycon"
(sha1: d50d7269ebcb438afa346cdffce0f4e2a1b9e831)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 26 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 10d51c2f10d7..adc1cd7c3bc7 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -921,6 +921,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
         earlycon=       [KNL] Output early console device and options.
 
+                cdns,<addr>
+                        Start an early, polled-mode console on a cadence serial
+                        port at the specified address. The cadence serial port
+                        must already be setup and configured. Options are not
+                        yet supported.
+
                 uart[8250],io,<addr>[,options]
                 uart[8250],mmio,<addr>[,options]
                 uart[8250],mmio32,<addr>[,options]
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 81f6ee7d4223..02a896f4dbcd 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1429,6 +1429,7 @@ config SERIAL_XILINX_PS_UART_CONSOLE
         bool "Cadence UART console support"
         depends on SERIAL_XILINX_PS_UART=y
         select SERIAL_CORE_CONSOLE
+        select SERIAL_EARLYCON
         help
           Enable a Cadence UART port to be the system console.
 
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 7f8027f27ab9..200c1af2141b 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1051,6 +1051,25 @@ static void cdns_uart_console_putchar(struct uart_port *port, int ch)
         cdns_uart_writel(ch, CDNS_UART_FIFO_OFFSET);
 }
 
+static void cdns_early_write(struct console *con, const char *s, unsigned n)
+{
+        struct earlycon_device *dev = con->data;
+
+        uart_console_write(&dev->port, s, n, cdns_uart_console_putchar);
+}
+
+static int __init cdns_early_console_setup(struct earlycon_device *device,
+                                           const char *opt)
+{
+        if (!device->port.membase)
+                return -ENODEV;
+
+        device->con->write = cdns_early_write;
+
+        return 0;
+}
+EARLYCON_DECLARE(cdns, cdns_early_console_setup);
+
 /**
  * cdns_uart_console_write - perform write operation
  * @co: Console handle