5 files changed, 134 insertions, 0 deletions

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 5416e28a7538..863d877e0b5f 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 5a7510e9d09d..dc590919f8eb 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 13b867093499..9d3fdcd66290 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 b0a518e97599..99464a7bdb3b 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 000000000000..ce5a7b489e4b
--- /dev/null
+++ b/arch/powerpc/sysdev/udbg_memcons.c
@@ -0,0 +1,105 @@
+/*
+ * A udbg backend which logs messages and reads input from in memory
+ * buffers.
+ *
+ * The console output can be read from memcons_output which is a
+ * circular buffer whose next write position is stored in memcons.output_pos.
+ *
+ * Input may be passed by writing into the memcons_input buffer when it is
+ * empty. The input buffer is empty when both input_pos == input_start and
+ * *input_start == '\0'.
+ *
+ * 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/barrier.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)
+{
+        char *new_output_pos;
+
+        *memcons.output_pos = c;
+        wmb();
+        new_output_pos = memcons.output_pos + 1;
+        if (new_output_pos >= memcons.output_end)
+                new_output_pos = memcons.output_start;
+
+        memcons.output_pos = new_output_pos;
+}
+
+int memcons_getc_poll(void)
+{
+        char c;
+        char *new_input_pos;
+
+        if (*memcons.input_pos) {
+                c = *memcons.input_pos;
+
+                new_input_pos = memcons.input_pos + 1;
+                if (new_input_pos >= memcons.input_end)
+                        new_input_pos = memcons.input_start;
+                else if (*new_input_pos == '\0')
+                        new_input_pos = memcons.input_start;
+
+                *memcons.input_pos = '\0';
+                wmb();
+                memcons.input_pos = new_input_pos;
+                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;
+}