serial: tegra: add serial driver

NVIDIA's Tegra has multiple UART controller which supports:
- APB DMA based controller fifo read/write.
- End Of Data interrupt in incoming data to know whether end
  of frame achieve or not.
- HW controlled RTS and CTS flow control to reduce SW overhead.

Add serial driver to use all above feature.
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt

+NVIDIA Tegra20/Tegra30 high speed (DMA based) UART controller driver.
+
+Required properties:
+- compatible : should be "nvidia,tegra30-hsuart", "nvidia,tegra20-hsuart".
+- reg: Should contain UART controller registers location and length.
+- interrupts: Should contain UART controller interrupts.
+- nvidia,dma-request-selector : The Tegra DMA controller's phandle and
+  request selector for this UART controller.
+
+Optional properties:
+- nvidia,enable-modem-interrupt: Enable modem interrupts. Should be enable
+		only if all 8 lines of UART controller are pinmuxed.
+
+Example:
+
+serial@70006000 {
+	compatible = "nvidia,tegra30-hsuart", "nvidia,tegra20-hsuart";
+	reg = <0x70006000 0x40>;
+	reg-shift = <2>;
+	interrupts = <0 36 0x04>;
+	nvidia,dma-request-selector = <&apbdma 8>;
+	nvidia,enable-modem-interrupt;
+	status = "disabled";
+};

drivers/tty/serial/Kconfig

@@ -269,6 +269,17 @@ config SERIAL_SIRFSOC_CONSOLE
           your boot loader about how to pass options to the kernel at
           boot time.)
 
+config SERIAL_TEGRA
+	tristate "NVIDIA Tegra20/30 SoC serial controller"
+	depends on ARCH_TEGRA && TEGRA20_APB_DMA
+	select SERIAL_CORE
+	help
+	  Support for the on-chip UARTs on the NVIDIA Tegra series SOCs
+	  providing /dev/ttyHS0, 1, 2, 3 and 4 (note, some machines may not
+	  provide all of these ports, depending on how the serial port
+	  are enabled). This driver uses the APB DMA to achieve higher baudrate
+	  and better performance.
+
 config SERIAL_MAX3100
 	tristate "MAX3100 support"
 	depends on SPI

drivers/tty/serial/Makefile

@@ -80,6 +80,7 @@ obj-$(CONFIG_SERIAL_MXS_AUART) += mxs-auart.o
 obj-$(CONFIG_SERIAL_LANTIQ)	+= lantiq.o
 obj-$(CONFIG_SERIAL_XILINX_PS_UART) += xilinx_uartps.o
 obj-$(CONFIG_SERIAL_SIRFSOC) += sirfsoc_uart.o
+obj-$(CONFIG_SERIAL_TEGRA) += serial-tegra.o
 obj-$(CONFIG_SERIAL_AR933X)   += ar933x_uart.o
 obj-$(CONFIG_SERIAL_EFM32_UART) += efm32-uart.o
 obj-$(CONFIG_SERIAL_ARC)	+= arc_uart.o