Add default crash console code to hook up to new console API

This patch expands the weak stubs for the plat_crash_console_xxx
functions in common platform code to use the new console API for crash
output. This should make crash console output "just work" for most cases
without the need for the platform to explicitly set up a crash console.
For cases where the normal console framework doesn't work (e.g. very
early crashes, before the platform can register any consoles), platforms
are still able to override the functions just like before.

This feature requires the MULTI_CONSOLE_API compile-time flag to work.
For builds which don't have it set, this patch has no practical effect.

Change-Id: I80dd161cb43f9db59a0bad2dae33c6560cfac584
Signed-off-by: Julius Werner <jwerner@chromium.org>

docs/porting-guide.rst

@@ -1846,12 +1846,8 @@ Function : bl31\_plat\_runtime\_setup() [optional]
 
 The purpose of this function is allow the platform to perform any BL31 runtime
 setup just prior to BL31 exit during cold boot. The default weak
-implementation of this function will invoke ``console_uninit()`` which will
-suppress any BL31 runtime logs.
-
-In ARM Standard platforms, this function will initialize the BL31 runtime
-console which will cause all further BL31 logs to be output to the
-runtime console.
+implementation of this function will invoke ``console_switch_state()`` to switch
+console output to consoles marked for use in the ``runtime`` state.
 
 Function : bl31\_get\_next\_image\_info() [mandatory]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -2619,14 +2615,20 @@ as Group 0 secure interrupt, Group 1 secure interrupt or Group 1 NS interrupt.
 Crash Reporting mechanism (in BL31)
 -----------------------------------
 
+NOTE: This section assumes that your platform is enabling the MULTI_CONSOLE_API
+flag in its platform.mk. Not using this flag is deprecated for new platforms.
+
 BL31 implements a crash reporting mechanism which prints the various registers
-of the CPU to enable quick crash analysis and debugging. It requires that a
-console is designated as the crash console by the platform which will be used to
-print the register dump.
+of the CPU to enable quick crash analysis and debugging. By default, the
+definitions in ``plat/common/aarch64/platform\_helpers.S`` will cause the crash
+output to be routed over the normal console infrastructure and get printed on
+consoles configured to output in crash state. ``console_set_scope()`` can be
+used to control whether a console is used for crash output.
 
-The following functions must be implemented by the platform if it wants crash
-reporting mechanism in BL31. The functions are implemented in assembly so that
-they can be invoked without a C Runtime stack.
+In some cases (such as debugging very early crashes that happen before the
+normal boot console can be set up), platforms may want to control crash output
+more explicitly. For these, the following functions can be overridden by
+platform code. They are executed outside of a C environment and without a stack.
 
 Function : plat\_crash\_console\_init
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -2637,9 +2639,30 @@ Function : plat\_crash\_console\_init
     Return   : int
 
 This API is used by the crash reporting mechanism to initialize the crash
-console. It must only use the general purpose registers x0 to x4 to do the
+console. It must only use the general purpose registers x0 through x7 to do the
 initialization and returns 1 on success.
 
+If you are trying to debug crashes before the console driver would normally get
+registered, you can use this to register a driver from assembly with hardcoded
+parameters. For example, you could register the 16550 driver like this:
+
+::
+
+    .section .data.crash_console      /* Reserve space for console structure */
+    crash_console:
+    .zero 6 * 8                       /* console_16550_t has 6 8-byte words */
+    func plat_crash_console_init
+        ldr     x0, =YOUR_16550_BASE_ADDR
+        ldr     x1, =YOUR_16550_SRCCLK_IN_HZ
+        ldr     x2, =YOUR_16550_TARGET_BAUD_RATE
+        adrp    x3, crash_console
+        add     x3, x3, :lo12:crash_console
+        b       console_16550_register  /* tail call, returns 1 on success */
+    endfunc plat_crash_console_init
+
+If you're trying to debug crashes in BL1, you can call the console_xxx_core_init
+function exported by some console drivers from here.
+
 Function : plat\_crash\_console\_putc
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -2653,6 +2676,12 @@ designated crash console. It must only use general purpose registers x1 and
 x2 to do its work. The parameter and the return value are in general purpose
 register x0.
 
+If you have registered a normal console driver in ``plat_crash_console_init``,
+you can keep the default implementation here (which calls ``console_putc()``).
+
+If you're trying to debug crashes in BL1, you can call the console_xxx_core_putc
+function exported by some console drivers from here.
+
 Function : plat\_crash\_console\_flush
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -2663,9 +2692,15 @@ Function : plat\_crash\_console\_flush
 
 This API is used by the crash reporting mechanism to force write of all buffered
 data on the designated crash console. It should only use general purpose
-registers x0 and x1 to do its work. The return value is 0 on successful
+registers x0 through x5 to do its work. The return value is 0 on successful
 completion; otherwise the return value is -1.
 
+If you have registered a normal console driver in ``plat_crash_console_init``,
+you can keep the default implementation here (which calls ``console_flush()``).
+
+If you're trying to debug crashes in BL1, you can call the console_xx_core_flush
+function exported by some console drivers from here.
+
 Build flags
 -----------
 

plat/common/aarch64/platform_helpers.S

@@ -6,6 +6,7 @@
 
 #include <arch.h>
 #include <asm_macros.S>
+#include <console.h>
 #include <platform_def.h>
 
 	.weak	plat_report_exception
@@ -56,33 +57,78 @@ func plat_report_exception
 	ret
 endfunc plat_report_exception
 
+#if MULTI_CONSOLE_API
 	/* -----------------------------------------------------
-	 * Placeholder function which should be redefined by
-	 * each platform.
+	 * int plat_crash_console_init(void)
+	 * Use normal console by default. Switch it to crash
+	 * mode so serial consoles become active again.
+	 * NOTE: This default implementation will only work for
+	 * crashes that occur after a normal console (marked
+	 * valid for the crash state) has been registered with
+	 * the console framework. To debug crashes that occur
+	 * earlier, the platform has to override these functions
+	 * with an implementation that initializes a console
+	 * driver with hardcoded parameters. See
+	 * docs/porting-guide.rst for more information.
 	 * -----------------------------------------------------
 	 */
 func plat_crash_console_init
+#if defined(IMAGE_BL1)
+	/*
+	 * BL1 code can possibly crash so early that the data segment is not yet
+	 * accessible. Don't risk undefined behavior by trying to run the normal
+	 * console framework. Platforms that want to debug BL1 will need to
+	 * override this with custom functions that can run from registers only.
+	 */
 	mov	x0, #0
 	ret
+#else	/* IMAGE_BL1 */
+	mov	x3, x30
+	mov	x0, #CONSOLE_FLAG_CRASH
+	bl	console_switch_state
+	mov	x0, #1
+	ret	x3
+#endif
 endfunc plat_crash_console_init
 
 	/* -----------------------------------------------------
-	 * Placeholder function which should be redefined by
-	 * each platform.
+	 * void plat_crash_console_putc(int character)
+	 * Output through the normal console by default.
 	 * -----------------------------------------------------
 	 */
 func plat_crash_console_putc
-	ret
+	b	console_putc
 endfunc plat_crash_console_putc
 
 	/* -----------------------------------------------------
-	 * Placeholder function which should be redefined by
-	 * each platform.
+	 * void plat_crash_console_flush(void)
+	 * Flush normal console by default.
+	 * -----------------------------------------------------
+	 */
+func plat_crash_console_flush
+	b	console_flush
+endfunc plat_crash_console_flush
+
+#else	/* MULTI_CONSOLE_API */
+
+	/* -----------------------------------------------------
+	 * In the old API these are all no-op stubs that need to
+	 * be overridden by the platform to be useful.
 	 * -----------------------------------------------------
 	 */
+func plat_crash_console_init
+	mov	x0, #0
+	ret
+endfunc plat_crash_console_init
+
+func plat_crash_console_putc
+	ret
+endfunc plat_crash_console_putc
+
 func plat_crash_console_flush
 	ret
 endfunc plat_crash_console_flush
+#endif
 
 	/* -----------------------------------------------------
 	 * Placeholder function which should be redefined by