[POWERPC] Add udbg support for RTAS console

Add udbg hooks for the RTAS console, based on the RTAS put-term-char
and get-term-char calls. Along with my previous patches, this should
enable debugging as soon as early_init_dt_scan_rtas() is called.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

4 files changed, 88 insertions, 4 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c5e01c4b637d..deea4c8e1f4e 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -420,6 +420,10 @@ config PPC_IBM_CELL_BLADE
         select MMIO_NVRAM
         select PPC_UDBG_16550
 
+config UDBG_RTAS_CONSOLE
+        bool
+        default n
+
 config XICS
         depends on PPC_PSERIES
         bool
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index c69006ae8246..e29ef77d3b00 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -134,12 +134,19 @@ config PPC_EARLY_DEBUG_G5
         help
           Select this to enable early debugging for Apple G5 machines.
 
-config PPC_EARLY_DEBUG_RTAS
+config PPC_EARLY_DEBUG_RTAS_PANEL
         bool "RTAS Panel"
         depends on PPC_RTAS
         help
           Select this to enable early debugging via the RTAS panel.
 
+config PPC_EARLY_DEBUG_RTAS_CONSOLE
+        bool "RTAS Console"
+        depends on PPC_RTAS
+        select UDBG_RTAS_CONSOLE
+        help
+          Select this to enable early debugging via the RTAS console.
+
 config PPC_EARLY_DEBUG_MAPLE
         bool "Maple real mode"
         depends on PPC_MAPLE
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 061d8afd246e..4a4cb5598402 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -109,11 +109,71 @@ static void call_rtas_display_status_delay(char c)
         }
 }
 
-void __init udbg_init_rtas(void)
+void __init udbg_init_rtas_panel(void)
 {
         udbg_putc = call_rtas_display_status_delay;
 }
 
+#ifdef CONFIG_UDBG_RTAS_CONSOLE
+
+/* If you think you're dying before early_init_dt_scan_rtas() does its
+ * work, you can hard code the token values for your firmware here and
+ * hardcode rtas.base/entry etc.
+ */
+static unsigned int rtas_putchar_token = RTAS_UNKNOWN_SERVICE;
+static unsigned int rtas_getchar_token = RTAS_UNKNOWN_SERVICE;
+
+static void udbg_rtascon_putc(char c)
+{
+        int tries;
+
+        if (!rtas.base)
+                return;
+
+        /* Add CRs before LFs */
+        if (c == '\n')
+                udbg_rtascon_putc('\r');
+
+        /* if there is more than one character to be displayed, wait a bit */
+        for (tries = 0; tries < 16; tries++) {
+                if (rtas_call(rtas_putchar_token, 1, 1, NULL, c) == 0)
+                        break;
+                udelay(1000);
+        }
+}
+
+static int udbg_rtascon_getc_poll(void)
+{
+        int c;
+
+        if (!rtas.base)
+                return -1;
+
+        if (rtas_call(rtas_getchar_token, 0, 2, &c))
+                return -1;
+
+        return c;
+}
+
+static int udbg_rtascon_getc(void)
+{
+        int c;
+
+        while ((c = udbg_rtascon_getc_poll()) == -1)
+                ;
+
+        return c;
+}
+
+
+void __init udbg_init_rtas_console(void)
+{
+        udbg_putc = udbg_rtascon_putc;
+        udbg_getc = udbg_rtascon_getc;
+        udbg_getc_poll = udbg_rtascon_getc_poll;
+}
+#endif /* CONFIG_UDBG_RTAS_CONSOLE */
+
 void rtas_progress(char *s, unsigned short hex)
 {
         struct device_node *root;
@@ -820,6 +880,16 @@ int __init early_init_dt_scan_rtas(unsigned long node,
                 rtas.size = *sizep;
         }
 
+#ifdef CONFIG_UDBG_RTAS_CONSOLE
+        basep = of_get_flat_dt_prop(node, "put-term-char", NULL);
+        if (basep)
+                rtas_putchar_token = *basep;
+
+        basep = of_get_flat_dt_prop(node, "get-term-char", NULL);
+        if (basep)
+                rtas_getchar_token = *basep;
+#endif
+
         /* break now */
         return 1;
 }
diff --git a/arch/powerpc/kernel/udbg.c b/arch/powerpc/kernel/udbg.c
index 67d9fd9ae2b5..759afd5e0d8a 100644
--- a/arch/powerpc/kernel/udbg.c
+++ b/arch/powerpc/kernel/udbg.c
@@ -34,9 +34,12 @@ void __init udbg_early_init(void)
 #elif defined(CONFIG_PPC_EARLY_DEBUG_G5)
         /* For use on Apple G5 machines */
         udbg_init_pmac_realmode();
-#elif defined(CONFIG_PPC_EARLY_DEBUG_RTAS)
+#elif defined(CONFIG_PPC_EARLY_DEBUG_RTAS_PANEL)
         /* RTAS panel debug */
-        udbg_init_rtas();
+        udbg_init_rtas_panel();
+#elif defined(CONFIG_PPC_EARLY_DEBUG_RTAS_CONSOLE)
+        /* RTAS console debug */
+        udbg_init_rtas_console();
 #elif defined(CONFIG_PPC_EARLY_DEBUG_MAPLE)
         /* Maple real mode debug */
         udbg_init_maple_realmode();