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Commit ffb7fcd6 authored by Vineet Gupta's avatar Vineet Gupta
Browse files

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: default avatarPeter Hurley <peter@hurleysoftware.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 7bf6df57

arch/arc/include/asm/serial.h

+5 −18
Original line number Diff line number Diff line
@@ -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 */

arch/arc/kernel/devtree.c

+24 −0
Original line number Diff line number Diff line
@@ -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;

}