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ARC: Dynamically determine BASE_BAUD from DeviceTree

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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>
This commit is contained in:
Vineet Gupta 2014-10-28 15:04:05 +05:30
parent 7bf6df575f
commit ffb7fcd66f
2 changed files with 29 additions and 18 deletions
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23
arch/arc/include/asm/serial.h
View file

@ -10,26 +10,13 @@
#define _ASM_ARC_SERIAL_H
/*
* early-8250 requires BASE_BAUD to be defined and includes this header.
* We put in a typical value:
* (core clk / 16) - i.e. UART samples 16 times per sec.
* Athough in multi-platform-image this might not work, specially if the
* clk driving the UART is different.
* We can't use DeviceTree as this is typically for early serial.
* early 8250 (now earlycon) requires BASE_BAUD to be defined in this header.
* However to still determine it dynamically (for multi-platform images)
* we do this in a helper by parsing the FDT early
*/
#include <asm/clk.h>
extern unsigned int __init arc_early_base_baud(void);
#define BASE_BAUD (arc_get_core_freq() / 16)
/*
* This is definitely going to break early 8250 consoles on multi-platform
* images but hey, it won't add any code complexity for a debug feature of
* one broken driver.
*/
#ifdef CONFIG_ARC_PLAT_TB10X
#undef BASE_BAUD
#define BASE_BAUD (arc_get_core_freq() / 16 / 3)
#endif
#define BASE_BAUD arc_early_base_baud()
#endif /* _ASM_ARC_SERIAL_H */

24
arch/arc/kernel/devtree.c
View file

@ -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;
}