[PATCH] powerpc: Add an in memory udbg console

[Benjamin Herrenschmidt]

On Mon, 2013-04-29 at 16:24 +1000, Alistair Popple wrote:
> This patch adds a new udbg early debug console which utilises
> statically defined input and output buffers stored within the kernel
> BSS. It is primarily designed to assist with bring up of new hardware
> which may not have a working console but which has a method of
> reading/writing kernel memory.

This probably need some memory barriers :-)

Cheers,
Ben.

> Signed-off-by: Alistair Popple <alistair at popple.id.au>
> ---
>  arch/powerpc/Kconfig.debug         |   23 ++++++++++
>  arch/powerpc/include/asm/udbg.h    |    1 +
>  arch/powerpc/kernel/udbg.c         |    3 ++
>  arch/powerpc/sysdev/Makefile       |    2 +
>  arch/powerpc/sysdev/udbg_memcons.c |   85 ++++++++++++++++++++++++++++++++++++
>  5 files changed, 114 insertions(+)
>  create mode 100644 arch/powerpc/sysdev/udbg_memcons.c
> 
> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> index 5416e28..863d877 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -262,8 +262,31 @@ config PPC_EARLY_DEBUG_OPAL_HVSI
>  	  Select this to enable early debugging for the PowerNV platform
>  	  using an "hvsi" console
>  
> +config PPC_EARLY_DEBUG_MEMCONS
> +	bool "In memory console"
> +	help
> +	  Select this to enable early debugging using an in memory console.
> +	  This console provides input and output buffers stored within the
> +	  kernel BSS and should be safe to select on any system. A debugger
> +	  can then be used to read kernel output or send input to the console.
>  endchoice
>  
> +config PPC_MEMCONS_OUTPUT_SIZE
> +	int "In memory console output buffer size"
> +	depends on PPC_EARLY_DEBUG_MEMCONS
> +	default 4096
> +	help
> +	  Selects the size of the output buffer (in bytes) of the in memory
> +	  console.
> +
> +config PPC_MEMCONS_INPUT_SIZE
> +	int "In memory console input buffer size"
> +	depends on PPC_EARLY_DEBUG_MEMCONS
> +	default 128
> +	help
> +	  Selects the size of the input buffer (in bytes) of the in memory
> +	  console.
> +
>  config PPC_EARLY_DEBUG_OPAL
>  	def_bool y
>  	depends on PPC_EARLY_DEBUG_OPAL_RAW || PPC_EARLY_DEBUG_OPAL_HVSI
> diff --git a/arch/powerpc/include/asm/udbg.h b/arch/powerpc/include/asm/udbg.h
> index 5a7510e..dc59091 100644
> --- a/arch/powerpc/include/asm/udbg.h
> +++ b/arch/powerpc/include/asm/udbg.h
> @@ -52,6 +52,7 @@ extern void __init udbg_init_40x_realmode(void);
>  extern void __init udbg_init_cpm(void);
>  extern void __init udbg_init_usbgecko(void);
>  extern void __init udbg_init_wsp(void);
> +extern void __init udbg_init_memcons(void);
>  extern void __init udbg_init_ehv_bc(void);
>  extern void __init udbg_init_ps3gelic(void);
>  extern void __init udbg_init_debug_opal_raw(void);
> diff --git a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
> index f974849..efa5c93 100644
> --- a/arch/powerpc/kernel/udbg.c
> +++ b/arch/powerpc/kernel/udbg.c
> @@ -64,6 +64,9 @@ void __init udbg_early_init(void)
>  	udbg_init_usbgecko();
>  #elif defined(CONFIG_PPC_EARLY_DEBUG_WSP)
>  	udbg_init_wsp();
> +#elif defined(CONFIG_PPC_EARLY_DEBUG_MEMCONS)
> +	/* In memory console */
> +	udbg_init_memcons();
>  #elif defined(CONFIG_PPC_EARLY_DEBUG_EHV_BC)
>  	udbg_init_ehv_bc();
>  #elif defined(CONFIG_PPC_EARLY_DEBUG_PS3GELIC)
> diff --git a/arch/powerpc/sysdev/Makefile b/arch/powerpc/sysdev/Makefile
> index b0a518e..99464a7 100644
> --- a/arch/powerpc/sysdev/Makefile
> +++ b/arch/powerpc/sysdev/Makefile
> @@ -64,6 +64,8 @@ endif
>  
>  obj-$(CONFIG_PPC_SCOM)		+= scom.o
>  
> +obj-$(CONFIG_PPC_EARLY_DEBUG_MEMCONS)	+= udbg_memcons.o
> +
>  subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror
>  
>  obj-$(CONFIG_PPC_XICS)		+= xics/
> diff --git a/arch/powerpc/sysdev/udbg_memcons.c b/arch/powerpc/sysdev/udbg_memcons.c
> new file mode 100644
> index 0000000..36f5c44
> --- /dev/null
> +++ b/arch/powerpc/sysdev/udbg_memcons.c
> @@ -0,0 +1,85 @@
> +/*
> + * A udbg backend which logs messages and reads input from in memory
> + * buffers.
> + *
> + * Copyright (C) 2003-2005 Anton Blanchard and Milton Miller, IBM Corp
> + * Copyright (C) 2013 Alistair Popple, IBM Corp
> + *
> + *      This program is free software; you can redistribute it and/or
> + *      modify it under the terms of the GNU General Public License
> + *      as published by the Free Software Foundation; either version
> + *      2 of the License, or (at your option) any later version.
> + */
> +
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <asm/page.h>
> +#include <asm/processor.h>
> +#include <asm/udbg.h>
> +
> +struct memcons {
> +	char *output_start;
> +	char *output_pos;
> +	char *output_end;
> +	char *input_start;
> +	char *input_pos;
> +	char *input_end;
> +};
> +
> +static char memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE];
> +static char memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE];
> +
> +struct memcons memcons = {
> +	.output_start = memcons_output,
> +	.output_pos = memcons_output,
> +	.output_end = &memcons_output[CONFIG_PPC_MEMCONS_OUTPUT_SIZE],
> +	.input_start = memcons_input,
> +	.input_pos = memcons_input,
> +	.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
> +};
> +
> +void memcons_putc(char c)
> +{
> +	*memcons.output_pos++ = c;
> +	if (memcons.output_pos >= memcons.output_end)
> +		memcons.output_pos = memcons.output_start;
> +}
> +
> +int memcons_getc_poll(void)
> +{
> +	char c;
> +
> +	if (*memcons.input_pos) {
> +		c = *memcons.input_pos;
> +		*memcons.input_pos++ = 0;
> +
> +		if (*memcons.input_pos == '\0' || memcons.input_pos >= memcons.input_end)
> +			memcons.input_pos = memcons.input_start;
> +
> +		return c;
> +	}
> +
> +	return -1;
> +}
> +
> +int memcons_getc(void)
> +{
> +	int c;
> +
> +	while (1) {
> +		c = memcons_getc_poll();
> +		if (c == -1)
> +			cpu_relax();
> +		else
> +			break;
> +	}
> +
> +	return c;
> +}
> +
> +void udbg_init_memcons(void)
> +{
> +	udbg_putc = memcons_putc;
> +	udbg_getc = memcons_getc;
> +	udbg_getc_poll = memcons_getc_poll;
> +}