[PATCH v3 4/8] ns8250: Move base clock definition to a header

[Benjamin Herrenschmidt]

And while at it, unify it as clock frequency in HZ, to match the
value in "struct grub_serial_config" and do the division by
16 in one common place.

This will simplify adding SPCR support.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 grub-core/term/ns8250.c | 15 ++++++++-------
 include/grub/ns8250.h   | 13 +++++++++++++
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/grub-core/term/ns8250.c b/grub-core/term/ns8250.c
index 43b9b3719..9e0ebff5a 100644
--- a/grub-core/term/ns8250.c
+++ b/grub-core/term/ns8250.c
@@ -37,12 +37,6 @@ static const grub_port_t serial_hw_io_addr[] = 
GRUB_MACHINE_SERIAL_PORTS;
 
 static int dead_ports = 0;
 
-#ifdef GRUB_MACHINE_MIPS_LOONGSON
-#define DEFAULT_BASE_CLOCK (2 * 115200)
-#else
-#define DEFAULT_BASE_CLOCK 115200
-#endif
-
 static grub_uint8_t
 ns8250_reg_read (struct grub_serial_port *port, grub_addr_t reg)
 {
@@ -71,7 +65,14 @@ serial_get_divisor (const struct grub_serial_port *port 
__attribute__ ((unused))
   grub_uint32_t divisor;
   grub_uint32_t actual_speed, error;
 
-  base_clock = config->base_clock ? (config->base_clock >> 4) : 
DEFAULT_BASE_CLOCK;
+  /* Get the UART input clock frequency */
+  base_clock = config->base_clock ? config->base_clock : 
UART_DEFAULT_BASE_CLOCK;
+
+  /*
+   * The UART uses 16 times oversampling for the BRG, so adjust the value
+   * accordingly to calculate the divisor.
+   */
+  base_clock >>= 4;
 
   divisor = (base_clock + (config->speed / 2)) / config->speed;
   if (config->speed == 0)
diff --git a/include/grub/ns8250.h b/include/grub/ns8250.h
index 7947ba9c9..697637912 100644
--- a/include/grub/ns8250.h
+++ b/include/grub/ns8250.h
@@ -70,6 +70,19 @@
 /* Turn on DTR, RTS, and OUT2.  */
 #define UART_ENABLE_OUT2       0x08
 
+/*
+ * Default clock input of the UART (feeds the baud rate generator)
+ *
+ * The standard value here is 1.8432 Mhz, which corresponds to
+ * 115200 bauds * 16 (16 times oversampling).
+ *
+ */
+#ifdef GRUB_MACHINE_MIPS_LOONGSON
+#define UART_DEFAULT_BASE_CLOCK ((2 * 115200) << 4)
+#else
+#define UART_DEFAULT_BASE_CLOCK (115200 << 4)
+#endif
+
 #ifndef ASM_FILE
 #include <grub/cpu/io.h>
 
-- 
2.34.1