Introduce low-level debug for ARM architecture

I have been in trouble for a while to debug some nasty problem where neighter a debugger nor printf() function is available.

I found the lowlevel debug feature in ARM Linux can be used as is in U-Boot too.

I tested this series on our SoCs (32bit ARM, specificly Coretex-A9). Because I was not sure about aarch64, I have this feature depend on "! ARM64".

1/6 and 2/6 refactor a bit and move CONFIG_ARM64 to Kconfig.

3/6 imports some source files from Linux 3.16 and
5/6 adds the Kconfig menu.

Masahiro Yamada (6):
vexpress64: kconfig: consolidate CONFIG_TARGET_VEXPRESS_AEMV8A_SEMI
kconfig: armv8: move CONFIG_ARM64 to Kconfig
arm: debug: import debug files from Linux 3.16
arm: debug: replace license blocks with SPDX
arm: debug: add Kconfig entries for lowlevel debug
arm: debug: adjust for U-Boot

 arch/arm/Kconfig                       |  13 +-
 arch/arm/Kconfig.debug                 |  64 ++++++
 arch/arm/cpu/armv8/Kconfig             |   7 +
 arch/arm/include/debug/8250.S          |  52 +++++
 arch/arm/lib/Makefile                  |   2 +
 arch/arm/lib/debug.S                   | 136 ++++++++++++
 board/armltd/vexpress64/Kconfig        |  24 --
 board/freescale/ls2085a/Kconfig        |   8 -
 configs/ls2085a_emu_D4_defconfig       |   2 +-
 configs/ls2085a_emu_defconfig          |   2 +-
 configs/ls2085a_simu_defconfig         |   2 +-
 configs/vexpress_aemv8a_defconfig      |   1 -
 configs/vexpress_aemv8a_semi_defconfig |   4 +-
 include/linux/serial_reg.h             | 388 +++++++++++++++++++++++++++++++++
 14 files changed, 664 insertions(+), 41 deletions(-)
 create mode 100644 arch/arm/Kconfig.debug
 create mode 100644 arch/arm/cpu/armv8/Kconfig
 create mode 100644 arch/arm/include/debug/8250.S
 create mode 100644 arch/arm/lib/debug.S
 create mode 100644 include/linux/serial_reg.h

1.9.1

We do not have to distinguish CONFIG_TARGET_VEXPRESS_AEMV8A_SEMI from CONFIG_TARGET_VEXPRESS_AEMV8A. Rename the former to the latter.

---

Changes in v3: None
Changes in v2: None

 arch/arm/Kconfig                       |  3 ---
 board/armltd/vexpress64/Kconfig        | 20 --------------------
 configs/vexpress_aemv8a_semi_defconfig |  2 +-
 3 files changed, 1 insertion(+), 24 deletions(-)

index 22f0f09..1a4abde 100644
@@ -461,9 +461,6 @@ config TEGRA
 config TARGET_VEXPRESS_AEMV8A
 	bool "Support vexpress_aemv8a"
 
-config TARGET_VEXPRESS_AEMV8A_SEMI
-	bool "Support vexpress_aemv8a_semi"
-
 config TARGET_LS2085A_EMU
 	bool "Support ls2085a_emu"
 

index 91eb8d2..d8c4e21 100644
@@ -17,23 +17,3 @@ config SYS_CONFIG_NAME
 	default "vexpress_aemv8a"
 
 endif
-
-if TARGET_VEXPRESS_AEMV8A_SEMI
-
-config SYS_CPU
-	string
-	default "armv8"
-
-config SYS_BOARD
-	string
-	default "vexpress64"
-
-config SYS_VENDOR
-	string
-	default "armltd"
-
-config SYS_CONFIG_NAME
-	string
-	default "vexpress_aemv8a"
-
-endif

index e6dd8e7..24b868c 100644
@@ -1,3 +1,3 @@
 CONFIG_SYS_EXTRA_OPTIONS="ARM64,SEMIHOSTING,BASE_FVP"
 CONFIG_ARM=y
-CONFIG_TARGET_VEXPRESS_AEMV8A_SEMI=y
+CONFIG_TARGET_VEXPRESS_AEMV8A=y

1.9.1

Tom, (or Albert if he is ready)

Could you apply these two, please?
http://patchwork.ozlabs.org/patch/384614/
http://patchwork.ozlabs.org/patch/384616/

This kind of patches tend to cause conflicts.

Best Regards
Masahiro Yamada

---

Changes in v3:
- Rebase on commit a1263632

Changes in v2: None

 arch/arm/Kconfig                       | 8 ++++++++
 arch/arm/cpu/armv8/Kconfig             | 7 +++++++
 board/armltd/vexpress64/Kconfig        | 4 ----
 board/freescale/ls2085a/Kconfig        | 8 --------
 configs/ls2085a_emu_D4_defconfig       | 2 +-
 configs/ls2085a_emu_defconfig          | 2 +-
 configs/ls2085a_simu_defconfig         | 2 +-
 configs/vexpress_aemv8a_defconfig      | 1 -
 configs/vexpress_aemv8a_semi_defconfig | 2 +-
 9 files changed, 19 insertions(+), 17 deletions(-)
 create mode 100644 arch/arm/cpu/armv8/Kconfig

index 1a4abde..e6bcec5 100644
@@ -5,6 +5,9 @@ config SYS_ARCH
 	string
 	default "arm"
 
+config ARM64
+	bool
+
 choice
 	prompt "Target select"
 

@@ -460,12 +463,15 @@ config TEGRA
 
 config TARGET_VEXPRESS_AEMV8A
 	bool "Support vexpress_aemv8a"
+	select ARM64
 
 config TARGET_LS2085A_EMU
 	bool "Support ls2085a_emu"
+	select ARM64
 
 config TARGET_LS2085A_SIMU
 	bool "Support ls2085a_simu"
+	select ARM64
 
 config TARGET_BALLOON3
 	bool "Support balloon3"

@@ -508,6 +514,8 @@ config TARGET_JORNADA
 
 endchoice
 
+source "arch/arm/cpu/armv8/Kconfig"
+
 source "arch/arm/cpu/arm926ejs/davinci/Kconfig"
 
 source "arch/arm/cpu/armv7/exynos/Kconfig"

new file mode 100644
index 0000000..af6a457
@@ -0,0 +1,7 @@
+if ARM64
+
+config SYS_CPU
+	string
+	default "armv8"
+
+endif

index d8c4e21..519c544 100644
@@ -1,9 +1,5 @@
 if TARGET_VEXPRESS_AEMV8A
 
-config SYS_CPU
-	string
-	default "armv8"
-
 config SYS_BOARD
 	string
 	default "vexpress64"

index 5655e18..f33ebcb 100644
@@ -1,9 +1,5 @@
 if TARGET_LS2085A_EMU
 
-config SYS_CPU
-	string
-	default "armv8"
-
 config SYS_BOARD
 	string
 	default "ls2085a"

@@ -24,10 +20,6 @@ endif
 
 if TARGET_LS2085A_SIMU
 
-config SYS_CPU
-	string
-	default "armv8"
-
 config SYS_BOARD
 	string
 	default "ls2085a"

index f2f6882..0bc36ed 100644
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="ARM64,EMU,SYS_FSL_DDR4"
+CONFIG_SYS_EXTRA_OPTIONS="EMU,SYS_FSL_DDR4"
 CONFIG_ARM=y
 CONFIG_TARGET_LS2085A_EMU=y

index 51ffa56..a2efec3 100644
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="ARM64,EMU"
+CONFIG_SYS_EXTRA_OPTIONS="EMU"
 CONFIG_ARM=y
 CONFIG_TARGET_LS2085A_EMU=y

index efa8e74..7563a75 100644
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="ARM64,SIMU"
+CONFIG_SYS_EXTRA_OPTIONS="SIMU"
 CONFIG_ARM=y
 CONFIG_TARGET_LS2085A_SIMU=y

index a335abc..9e0a175 100644
@@ -1,3 +1,2 @@
-CONFIG_SYS_EXTRA_OPTIONS="ARM64"
 CONFIG_ARM=y
 CONFIG_TARGET_VEXPRESS_AEMV8A=y

index 24b868c..8fdf4e0 100644
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="ARM64,SEMIHOSTING,BASE_FVP"
+CONFIG_SYS_EXTRA_OPTIONS="SEMIHOSTING,BASE_FVP"
 CONFIG_ARM=y
 CONFIG_TARGET_VEXPRESS_AEMV8A=y

1.9.1

U-Boot does not have arch/arm/kernel, include/uapi directories, This commit copies files as follows:

Location in Linux -> Location in U-Boot

arch/arm/kernel/debug.S -> arch/arm/lib/debug.S
arch/arm/include/debug/8250.S -> arch/arm/include/debug/8250.S
include/uapi/linux/serial_reg.h -> include/linux/serial_reg.h

---

Changes in v3: None
Changes in v2: None

 arch/arm/include/debug/8250.S |  54 ++++++
 arch/arm/lib/debug.S          | 138 +++++++++++++++
 include/linux/serial_reg.h    | 389 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 581 insertions(+)
 create mode 100644 arch/arm/include/debug/8250.S
 create mode 100644 arch/arm/lib/debug.S
 create mode 100644 include/linux/serial_reg.h

new file mode 100644
index 0000000..7a2baf9
@@ -0,0 +1,54 @@
+/*
+ * arch/arm/include/debug/8250.S
+ *
+ *  Copyright (C) 1994-2013 Russell King
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/serial_reg.h>
+
+		.macro	addruart, rp, rv, tmp
+		ldr	\rp, =CONFIG_DEBUG_UART_PHYS
+		ldr	\rv, =CONFIG_DEBUG_UART_VIRT
+		.endm
+
+#ifdef CONFIG_DEBUG_UART_8250_WORD
+		.macro	store, rd, rx:vararg
+		str	\rd, \rx
+		.endm
+
+		.macro	load, rd, rx:vararg
+		ldr	\rd, \rx
+		.endm
+#else
+		.macro	store, rd, rx:vararg
+		strb	\rd, \rx
+		.endm
+
+		.macro	load, rd, rx:vararg
+		ldrb	\rd, \rx
+		.endm
+#endif
+
+#define UART_SHIFT CONFIG_DEBUG_UART_8250_SHIFT
+
+		.macro	senduart,rd,rx
+		store	\rd, [\rx, #UART_TX << UART_SHIFT]
+		.endm
+
+		.macro	busyuart,rd,rx
+1002:		load	\rd, [\rx, #UART_LSR << UART_SHIFT]
+		and	\rd, \rd, #UART_LSR_TEMT | UART_LSR_THRE
+		teq	\rd, #UART_LSR_TEMT | UART_LSR_THRE
+		bne	1002b
+		.endm
+
+		.macro	waituart,rd,rx
+#ifdef CONFIG_DEBUG_UART_8250_FLOW_CONTROL
+1001:		load	\rd, [\rx, #UART_MSR << UART_SHIFT]
+		tst	\rd, #UART_MSR_CTS
+		beq	1001b
+#endif
+		.endm

1.9.1

---

Changes in v3: None
Changes in v2: None

 arch/arm/include/debug/8250.S | 4 +---
 arch/arm/lib/debug.S          | 4 +---
 include/linux/serial_reg.h    | 5 ++---
 3 files changed, 4 insertions(+), 9 deletions(-)

index 7a2baf9..d47a892 100644
@@ -3,9 +3,7 @@
  *
  *  Copyright (C) 1994-2013 Russell King
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
+ * SPDX-License-Identifier:	GPL-2.0+
  */
 #include <linux/serial_reg.h>
 

index 14f7c3b..ddee7c0 100644
@@ -3,9 +3,7 @@
  *
  *  Copyright (C) 1994-1999 Russell King
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
+ * SPDX-License-Identifier:	GPL-2.0+
  *
  *  32-bit debugging code
  */

index 99b4705..9214b67 100644
@@ -2,9 +2,8 @@
  * include/linux/serial_reg.h
  *
  * Copyright (C) 1992, 1994 by Theodore Ts'o.
- * 
- * Redistribution of this file is permitted under the terms of the GNU 
- * Public License (GPL)
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
  * 
  * These are the UART port assignments, expressed as offsets from the base
  * register.  These assignments should hold for any serial port based on

1.9.1

We have not had a good method to debug the early boot stage such as lowlevel_init function. I guess developers generally use dedicated debuggers for that, but it is difficult in some cases. (For example, my debugger cannot connect to the ARM processor when it is in the secure state. It sometimes happens when I need to debug the early boot stage on ARM SoCs with secure extension.)

The low level debug feature in Linux would be also helpful for U-boot when we are stucking in nasty problems where the console is not available yet.

You have to enable CONFIG_DEBUG_LL to use this feature. For now, only 8250-compatible UART devices are supported. You can add a header file under arch/arm/include/debug/ directory to support your UART device if necessary.

---

Changes in v3: None
Changes in v2: None

 arch/arm/Kconfig       |  2 ++
 arch/arm/Kconfig.debug | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++
 arch/arm/lib/Makefile  |  2 ++
 3 files changed, 68 insertions(+)
 create mode 100644 arch/arm/Kconfig.debug

index e6bcec5..9cdd5f0 100644
@@ -681,4 +681,6 @@ source "board/woodburn/Kconfig"
 source "board/xaeniax/Kconfig"
 source "board/zipitz2/Kconfig"
 
+source "arch/arm/Kconfig.debug"
+
 endmenu

index 1ef2400..d74e4b8 100644
@@ -48,6 +48,8 @@ ifndef CONFIG_ARM64
 obj-y	+= cache-cp15.o
 endif
 
+obj-$(CONFIG_DEBUG_LL)	+= debug.o
+
 # For EABI conformant tool chains, provide eabi_compat()
 ifneq (,$(findstring -mabi=aapcs-linux,$(PLATFORM_CPPFLAGS)))
 extra-y	+= eabi_compat.o

1.9.1

Hi Masahiro,

Is it possible to use the existing drivers for this? It seems unfortunate to duplicate the ns16550 driver (if that is what has happened).

E.g. I have had good luck just calling that driver code directly. I'm not sure of an overall framework but it must be possible...

Regards,
Simon

Hi Simon,

I am afraid it is difficult since the serial drivers are too complicated and written in C.
Indeed, it is unfortunate, though.

This low level debug framework only uses r0, r1, r2, r3 registers and does not need stack.

I think it has an advantage over the serial drivers for debugging the lowlevel_init where no stack is ready.

Best Regards
Masahiro Yamada

Hi Masahiro,

We have CONFIG_SYS_INIT_SP_ADDR and the like - if there is no RAM available for a stack then I would question what RAM you are using to hold your code :-)

As an example, for ns16500, you can do something like:

ldr r0, =UART_BASE
ldr r0, =UART_BAUD_DIVISOR
bl NS16550_init

ldr r0, =UART_BASE
mov r1, #'a'
bl NS16550_putc

At least for ARMv7, this actually uses no stack, so you could do that now. I am pretty sure you would find the same with other serial drivers as they are very simple. The cost is that we need to be able to call the output function directly. With driver model we could require this to be part of the API and I'm pretty sure it would be easy enough. I still think this is far preferable to rewriting duplicate drivers in assembler. May this is the only possible way in Linux...

Also you can do:

ldr sp, =CONFIG_SYS_INIT_SP_ADDR

if needed.

Regards,
Simon

No, the point of this driver (and the similar ones that exist here and elsewhere) is to have something small and seperate that we know is not the cause of the problem.

Tom
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Hi Tom,

Please see my other email on this thread. I'm not talking about use the driver in full, just directly calling the driver's init and putc functions from assembler instead of duplicating them. It seems more scaleable to me in that we can support any driver in principle. The cost is that each driver needs to export these two functions with a defined signature.

Regards,
Simon

Because CONFIG_MMU is never defined in U-Boot,
the non-MMU code in debug.S is always used.

Unfortunately, the number of arguments of the addruart macro in Linux is different between MMU and non-MMU.
This causes a build error when importing some debug macros using the third argument. (For ex. arch/arm/include/debug/exynos.S) Pass the third argument to the non-MMU addruart to avoid such a problem.

---

Changes in v3: None
Changes in v2:
- Newly added

 arch/arm/lib/debug.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index ddee7c0..760ba74 100644
@@ -33,7 +33,7 @@
 
 #else /* !CONFIG_MMU */
 		.macro	addruart_current, rx, tmp1, tmp2
-		addruart	\rx, \tmp1
+		addruart	\rx, \tmp1, \tmp2
 		.endm
 
 #endif /* CONFIG_MMU */

1.9.1

Hello Masahiro,

Patches 3 through 6 also applied, to u-boot-arm/master. Thanks!

Amicalement,

Albert.