[U-Boot] [PATCH v2] serial: Add serial driver for Intel MID

[Andy Shevchenko]

Add a specific serial driver for Intel MID platforms.

It has special fractional divider which can be programmed via UART_PS,
UART_MUL, and UART_DIV registers.

The UART clock is calculated as

	UART clock = XTAL * UART_MUL / UART_DIV

The baudrate is calculated as

	baud rate = UART clock / UART_PS / DLAB

Initialize fractional divider correctly for Intel Edison platform.

For backward compatibility we have to set initial DLAB value to 16
and speed to 115200 baud, where initial frequency is 29491200Hz, and
XTAL frequency is 38.4MHz.

Signed-off-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
---
 drivers/serial/Kconfig      |  9 ++++++
 drivers/serial/Makefile     |  1 +
 drivers/serial/serial_mid.c | 71 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 drivers/serial/serial_mid.c

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index b11f3ff89e..1fb5a7b17d 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -398,6 +398,15 @@ config MESON_SERIAL
 	  If you have an Amlogic Meson based board and want to use the on-chip
 	  serial ports, say Y to this option. If unsure, say N.
 
+config MID_SERIAL
+	bool "Intel MID platform UART support"
+	depends on DM_SERIAL && OF_CONTROL
+	select SYS_NS16550
+	help
+	  Select this to enable a UART for Intel MID platforms.
+	  This uses the ns16550 driver as a library which is selected by
+	  default.
+
 config MSM_SERIAL
 	bool "Qualcomm on-chip UART"
 	depends on DM_SERIAL
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index 8430668bf9..61535212aa 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -28,6 +28,7 @@ obj-$(CONFIG_S5P) += serial_s5p.o
 obj-$(CONFIG_MXC_UART) += serial_mxc.o
 obj-$(CONFIG_PXA_SERIAL) += serial_pxa.o
 obj-$(CONFIG_MESON_SERIAL) += serial_meson.o
+obj-$(CONFIG_MID_SERIAL) += serial_mid.o
 ifdef CONFIG_SPL_BUILD
 obj-$(CONFIG_ROCKCHIP_SERIAL) += serial_rockchip.o
 endif
diff --git a/drivers/serial/serial_mid.c b/drivers/serial/serial_mid.c
new file mode 100644
index 0000000000..eb91ffc7d4
--- /dev/null
+++ b/drivers/serial/serial_mid.c
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2017 Intel Corporation
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <debug_uart.h>
+#include <dm.h>
+#include <dt-structs.h>
+#include <ns16550.h>
+#include <serial.h>
+
+/*
+ * The UART clock is calculated as
+ *
+ *	UART clock = XTAL * UART_MUL / UART_DIV
+ *
+ * The baudrate is calculated as
+ *
+ *	baud rate = UART clock / UART_PS / DLAB
+ */
+#define UART_PS		0x30
+#define UART_MUL	0x34
+#define UART_DIV	0x38
+
+static void mid_writel(struct ns16550_platdata *plat, int offset, int value)
+{
+	unsigned char *addr;
+
+	offset *= 1 << plat->reg_shift;
+	addr = (unsigned char *)plat->base + offset;
+
+	writel(value, addr + plat->reg_offset);
+}
+
+static int mid_serial_probe(struct udevice *dev)
+{
+	struct ns16550_platdata *plat = dev_get_platdata(dev);
+
+	/*
+	 * Initialize fractional divider correctly for Intel Edison
+	 * platform.
+	 *
+	 * For backward compatibility we have to set initial DLAB value
+	 * to 16 and speed to 115200 baud, where initial frequency is
+	 * 29491200Hz, and XTAL frequency is 38.4MHz.
+	 */
+	mid_writel(plat, UART_MUL, 96);
+	mid_writel(plat, UART_DIV, 125);
+	mid_writel(plat, UART_PS, 16);
+
+	return ns16550_serial_probe(dev);
+}
+
+static const struct udevice_id mid_serial_ids[] = {
+	{ .compatible = "intel,mid-uart" },
+	{}
+};
+
+U_BOOT_DRIVER(mid_uart) = {
+	.name	= "mid_uart",
+	.id	= UCLASS_SERIAL,
+	.of_match = mid_serial_ids,
+	.ofdata_to_platdata = ns16550_serial_ofdata_to_platdata,
+	.platdata_auto_alloc_size = sizeof(struct ns16550_platdata),
+	.priv_auto_alloc_size = sizeof(struct NS16550),
+	.probe	= mid_serial_probe,
+	.ops	= &ns16550_serial_ops,
+	.flags	= DM_FLAG_PRE_RELOC,
+};
-- 
2.11.0