On 01/06/2015 06:29 AM, Vineet Gupta wrote:
> This resolves the BASE_BAUD issue in Multiplatform images
This commit log could be improved. Something like:
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).
Regards,
Peter Hurley
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxx>
> Cc: linux-serial@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: Rob Herring <robh@xxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> ---
> arch/arc/include/asm/serial.h | 23 +++++------------------
> arch/arc/kernel/devtree.c | 24 ++++++++++++++++++++++++
> 2 files changed, 29 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arc/include/asm/serial.h b/arch/arc/include/asm/serial.h
> index 602b0970a764..744a6ae15754 100644
> --- a/arch/arc/include/asm/serial.h
> +++ b/arch/arc/include/asm/serial.h
> @@ -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 */
> diff --git a/arch/arc/kernel/devtree.c b/arch/arc/kernel/devtree.c
> index fffdb5e41b20..69a790cd9b6e 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 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;
> }
>
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