ARC: Dynamically determine BASE_BAUD from DeviceTree

8250 earlycon is broken on multi-platform ARC because the UART clk
value (BASE_BAUD) is fixed at build time.

Instead, determine the appropriate UART clk at runtime; parse the
devicetree early for platforms requiring alternate UART clk values
(currently only the TB10X platform).

Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/arc/kernel/devtree.c b/arch/arc/kernel/devtree.c
index fffdb5e41b20..5036d4c06996 100644
--- a/arch/arc/kernel/devtree.c
+++ b/arch/arc/kernel/devtree.c
@@ -17,6 +17,28 @@
 #include <asm/clk.h>
 #include <asm/mach_desc.h>
 
+#ifdef CONFIG_SERIAL_8250_CONSOLE
+
+static unsigned int __initdata arc_base_baud;
+
+unsigned int __init arc_early_base_baud(void)
+{
+        return arc_base_baud/16;
+}
+
+static void __init arc_set_early_base_baud(unsigned long dt_root)
+{
+        unsigned int core_clk = arc_get_core_freq();
+
+        if (of_flat_dt_is_compatible(dt_root, "abilis,arc-tb10x"))
+                arc_base_baud = core_clk/3;
+        else
+                arc_base_baud = core_clk;
+}
+#else
+#define arc_set_early_base_baud(dt_root)
+#endif
+
 static const void * __init arch_get_next_mach(const char *const **match)
 {
         static const struct machine_desc *mdesc = __arch_info_begin;
@@ -56,5 +78,7 @@ const struct machine_desc * __init setup_machine_fdt(void *dt)
         if (clk)
                 arc_set_core_freq(of_read_ulong(clk, len/4));
 
+        arc_set_early_base_baud(dt_root);
+
         return mdesc;
 }