[PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Jiaxun Yang]

Hi all,

This is a attempt to bring all low-level debugging print functions
together and provide a arm-like low-level debugging interface and
a further capability to debug early exceptions.

This patch elimiate platform specific early_printk, zboot printing
functions and cps-vec-ns16550 by newly introduced debug_ll.

Hope you'll find them handy :-)

Happy hacking!

Thanks

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
Changes in v3:
- Collect review tags
- Fix an indentation
- Link to v2: https://lore.kernel.org/r/20240326-mips_debug_ll-v2-0-b64abc76f2a1@flygoat.com

---
Jiaxun Yang (9):
      MIPS: asm: Move strings to .rodata.str section
      MIPS: debug: Implement low-level debugging functions
      MIPS: debug: Hook up DEBUG_LL with early printk
      MIPS: debug: Provide an early exception vector for low-level debugging
      MIPS: debug_ll: Add Kconfig symbols for some 8250 uarts
      MIPS: debug_ll: Implement support for Alchemy uarts
      MIPS: debug_ll: Implement support for AR933X uarts
      MIPS: zboot: Convert to use debug_ll facilities
      MIPS: CPS: Convert to use debug_ll facilities

 arch/mips/Kconfig                        |  12 +-
 arch/mips/Kconfig.debug                  | 240 +++++++++++++++++++++++--------
 arch/mips/boot/compressed/Makefile       |   9 +-
 arch/mips/boot/compressed/dbg.c          |  39 -----
 arch/mips/boot/compressed/debug-vec.S    |   3 +
 arch/mips/boot/compressed/debug.S        |   3 +
 arch/mips/boot/compressed/decompress.h   |   8 +-
 arch/mips/boot/compressed/head.S         |   6 +
 arch/mips/boot/compressed/uart-16550.c   |  49 -------
 arch/mips/boot/compressed/uart-alchemy.c |   9 --
 arch/mips/boot/compressed/uart-ath79.c   |   2 -
 arch/mips/boot/compressed/uart-prom.c    |   9 --
 arch/mips/include/asm/asm.h              |   2 +-
 arch/mips/include/debug/8250.S           |  60 ++++++++
 arch/mips/include/debug/alchemy.S        |  46 ++++++
 arch/mips/include/debug/ar933x.S         |  41 ++++++
 arch/mips/include/debug/uhi.S            |  48 +++++++
 arch/mips/kernel/Makefile                |   4 +-
 arch/mips/kernel/cps-vec.S               |  16 +--
 arch/mips/kernel/debug-vec.S             | 194 +++++++++++++++++++++++++
 arch/mips/kernel/debug.S                 | 130 +++++++++++++++++
 arch/mips/kernel/early_printk.c          |  19 +++
 arch/mips/kernel/head.S                  |   4 +
 23 files changed, 756 insertions(+), 197 deletions(-)
---
base-commit: 084c8e315db34b59d38d06e684b1a0dd07d30287
change-id: 20240326-mips_debug_ll-ce72fee1b6a2

Best regards,
-- 
Jiaxun Yang <jiaxun.yang@flygoat.com>

[PATCH v3 1/9] MIPS: asm: Move strings to .rodata.str section

[Jiaxun Yang]

Well, they are read only.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
v3: Fix an indentation error (philmd)
---
 arch/mips/include/asm/asm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/asm.h b/arch/mips/include/asm/asm.h
index 2e99450f4228..0c87a7de2a7d 100644
--- a/arch/mips/include/asm/asm.h
+++ b/arch/mips/include/asm/asm.h
@@ -94,7 +94,7 @@ symbol:		.insn
 symbol		=	value
 
 #define TEXT(msg)					\
-		.pushsection .data;			\
+		.pushsection .rodata.str;		\
 8:		.asciiz msg;				\
 		.popsection;
 

-- 
2.34.1

[PATCH v3 2/9] MIPS: debug: Implement low-level debugging functions

[Jiaxun Yang]

Currently we have three sets of early debugging functions
for MIPS: zboot putc/puts, cps-vec-ns16550, and prom_putc.

This is a attempt to bring them all to one by providing
a interface similar to arm's debug_ll, which is very portable
and allows you to support new platforms easily.

Two examples of output interfaces are provided, including
8250 uart and MIPS UHI semihosting, which already covered
most of the platforms.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug        |  80 +++++++++++++++++++++++++
 arch/mips/include/debug/8250.S |  60 +++++++++++++++++++
 arch/mips/include/debug/uhi.S  |  48 +++++++++++++++
 arch/mips/kernel/Makefile      |   2 +
 arch/mips/kernel/debug.S       | 130 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 320 insertions(+)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index f4ae7900fcd3..892e31804982 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -164,3 +164,83 @@ config MIPS_CPS_NS16550_WIDTH
 	  lb/sb instructions.
 
 endif # MIPS_CPS_NS16550_BOOL
+
+# These options are only for real kernel hackers who want to get their hands dirty.
+config DEBUG_LL
+	bool "Kernel low-level debugging functions (read help!)"
+	depends on DEBUG_KERNEL
+	help
+	  Say Y here to include definitions of printascii, printch, printhex
+	  in the kernel.  This is helpful if you are debugging code that
+	  executes before the console is initialized.
+
+	  Note that selecting this option will limit the kernel to a single
+	  UART or semihosting definition, as specified below. Attempting to
+	  boot the kernel image on a different platform *will not work*, so
+	  this option should not be enabled for kernels that are intended to
+	  be portable.
+
+choice
+	prompt "Kernel low-level debugging port"
+	depends on DEBUG_LL
+
+	config DEBUG_MIPS_UHI
+		bool "Kernel low-level debugging via UHI semihosting"
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  via MIPS UHI semihosting.
+
+	config DEBUG_LL_UART_8250
+		bool "Kernel low-level debugging via 8250 UART"
+		select DEBUG_LL_UART
+		help
+		  Say Y here if you wish the debug print routes to direct
+		  their output to an 8250 UART.  You can use this option
+		  to provide the parameters for the 8250 UART rather than
+		  selecting one of the platform specific options below if
+		  you know the parameters for the port.
+
+endchoice
+
+config DEBUG_LL_INCLUDE
+	string
+	default "debug/8250.S" if DEBUG_LL_UART_8250 || DEBUG_UART_8250
+	default "debug/uhi.S" if DEBUG_MIPS_UHI
+	default "debug-macro.S"
+
+# Compatibility options for 8250
+config DEBUG_UART_8250
+	bool
+	select DEBUG_LL_UART
+
+config DEBUG_LL_UART
+	bool
+
+config DEBUG_UART_FLOW_CONTROL
+	bool "Enable flow control (CTS) for the debug UART"
+	depends on DEBUG_LL_UART
+	default n
+	help
+	  Some UART ports are connected to terminals that will use modem
+	  control signals to indicate whether they are ready to receive text.
+	  In practice this means that the terminal is asserting the special
+	  control signal CTS (Clear To Send). If your debug UART supports
+	  this and your debug terminal will require it, enable this option.
+
+config DEBUG_UART_PHYS
+	hex "Physical base address of debug UART"
+	depends on DEBUG_LL_UART
+	help
+	  This is the physical base address of the debug UART. It must be
+	  accessible from unmapped kernel space (i.e. KSEG1 for 32bit kernels
+	  or XKPHYS for 64bit kernels).
+
+config DEBUG_UART_8250_SHIFT
+	int "Register offset shift for the 8250 debug UART"
+	depends on DEBUG_LL_UART_8250 || DEBUG_UART_8250
+	default 2
+
+config DEBUG_UART_8250_WIDTH
+	int "Register width for the 8250 debug UART"
+	depends on DEBUG_LL_UART_8250 || DEBUG_UART_8250
+	default 1
diff --git a/arch/mips/include/debug/8250.S b/arch/mips/include/debug/8250.S
new file mode 100644
index 000000000000..f8608d3e271a
--- /dev/null
+++ b/arch/mips/include/debug/8250.S
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@flygoat.com>
+ * MIPS Low level debug include file for 8250 UART
+ */
+
+#include <asm/addrspace.h>
+#include <asm/asm.h>
+#include <linux/serial_reg.h>
+
+#define DEBUG_LL_UART
+
+#define UART_BASE	CKSEG1ADDR(CONFIG_DEBUG_UART_PHYS)
+
+#define UART_TX_OFS	(UART_TX  << CONFIG_DEBUG_UART_8250_SHIFT)
+#define UART_LSR_OFS	(UART_LSR << CONFIG_DEBUG_UART_8250_SHIFT)
+#define UART_MSR_OFS	(UART_MSR << CONFIG_DEBUG_UART_8250_SHIFT)
+
+#if CONFIG_DEBUG_UART_8250_WIDTH == 1
+# define UART_L		lb
+# define UART_S		sb
+#elif CONFIG_DEBUG_UART_8250_WIDTH == 2
+# define UART_L		lh
+# define UART_S		sh
+#elif CONFIG_DEBUG_UART_8250_WIDTH == 4
+# define UART_L		lw
+# define UART_S		sw
+#elif defined(CONFIG_64BIT) && CONFIG_DEBUG_UART_8250_WIDTH == 8
+# define UART_L		ld
+# define UART_S		sd
+#else
+# define UART_L		lb
+# define UART_S		sb
+#endif
+
+		.macro	addruart,rd,rx
+		PTR_LA	\rd, UART_BASE
+		.endm
+
+		.macro	senduart,rd,rx
+		UART_S   \rd, UART_TX_OFS(\rx)
+		.endm
+
+		.macro	busyuart,rd,rx
+1002:
+		UART_L	\rd, UART_LSR_OFS(\rx)
+		andi	\rd, \rd, (UART_LSR_TEMT | UART_LSR_THRE)
+		xori	\rd, (UART_LSR_TEMT | UART_LSR_THRE)
+		bnez	\rd, 1002b
+		.endm
+
+		.macro	waituarttxrdy,rd,rx
+		.endm
+
+		.macro	waituartcts,rd,rx
+1001:
+		UART_L	\rd, UART_MSR_OFS(\rx)
+		andi	\rd, UART_MSR_CTS
+		beqz	\rd, 1001b
+		.endm
diff --git a/arch/mips/include/debug/uhi.S b/arch/mips/include/debug/uhi.S
new file mode 100644
index 000000000000..20554523e151
--- /dev/null
+++ b/arch/mips/include/debug/uhi.S
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@flygoat.com>
+ * MIPS Low level debug include file for UHI semihosting
+ */
+
+#include <asm/asm.h>
+
+/**
+ * printch() - write a character to UHI Plog
+ * @a0: ASCII character to write
+ *
+ * clobbers v0, t9
+ * UHI may clobber k0, k1
+ */
+		.pushsection .bss
+charbuf_addr:	.space 8
+		.popsection
+NESTED(printch, 0, ra)
+	PTR_LI	t9, charbuf_addr
+	sb	a0, 0(t9)
+	sb	zero, 1(t9)
+	move	a0, t9
+	li	v0, 0x1
+	li	t9, 13 /* plog */
+	.set push
+	.set MIPS_ISA_LEVEL_RAW
+	sdbbp	1
+	.set pop
+	jr	ra
+	END(printch)
+
+/**
+ * printascii() - write a string to UHI Plog
+ * @a0: pointer to NULL-terminated ASCII string
+ *
+ * clobbers v0
+ * UHI may clobber k0, k1
+ */
+NESTED(printascii, 0, ra)
+	li	v0, 0x1
+	li	t9, 13 /* plog */
+	.set push
+	.set MIPS_ISA_LEVEL_RAW
+	sdbbp	1
+	.set pop
+	jr		ra
+	END(printascii)
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index ecf3278a32f7..bfac35a64ae5 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -78,6 +78,8 @@ obj-$(CONFIG_MIPS32_COMPAT)	+= linux32.o ptrace32.o signal32.o
 obj-$(CONFIG_MIPS32_N32)	+= scall64-n32.o signal_n32.o
 obj-$(CONFIG_MIPS32_O32)	+= scall64-o32.o signal_o32.o
 
+obj-$(CONFIG_DEBUG_LL)		+= debug.o
+
 obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_PROC_FS)		+= proc.o
 obj-$(CONFIG_MAGIC_SYSRQ)	+= sysrq.o
diff --git a/arch/mips/kernel/debug.S b/arch/mips/kernel/debug.S
new file mode 100644
index 000000000000..a78d9a55bb35
--- /dev/null
+++ b/arch/mips/kernel/debug.S
@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@flygoat.com>
+ * MIPS Low level debug routines
+ *
+ * Note: Those functions are designed carefully to only clobber
+ * t0, t1, t9, so they can be used without stack. Also they are
+ * position independent to be called from any place.
+ */
+
+#include <linux/compiler.h>
+
+#include <asm/addrspace.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/mipsregs.h>
+#include <asm/regdef.h>
+
+#include CONFIG_DEBUG_LL_INCLUDE
+
+#ifdef DEBUG_LL_UART
+/**
+ * printch() - write a character to the UART
+ * @a0: ASCII character to write
+ *
+ * clobbers t0, t9
+ */
+NESTED(printch, 0, ra)
+	addruart	t9, t0
+#ifdef CONFIG_DEBUG_UART_FLOW_CONTROL
+	waituartcts	t0, t9
+#endif
+	waituarttxrdy	t0, t9
+	senduart	a0, t9
+	busyuart	t0, t9
+	jr		ra
+	END(printch)
+
+/**
+ * printascii() - write a string to the UART
+ * @a0: pointer to NULL-terminated ASCII string
+ *
+ * clobbers t0, t1, t9
+ *
+ * Write a null-terminated ASCII string to the UART.
+ */
+NESTED(printascii, 0, ra)
+	addruart	t9, t0
+	move		t1, a0
+
+1:	lb		a0, 0(t1)
+	beqz		a0, 2f
+#ifdef CONFIG_DEBUG_UART_FLOW_CONTROL
+	waituartcts	t0, t9
+#endif
+	waituarttxrdy	t0, t9
+	senduart	a0, t9
+	busyuart	t0, t9
+	PTR_ADDIU	t1, t1, 1
+	b		1b
+
+2:	jr		ra
+	END(printascii)
+#endif /* DEBUG_LL_UART */
+
+/**
+ * printhex() - write n byte hex value to the UART
+ * @a0: Hex value to write to the UART
+ * @a1: number of bytes to write to the UART
+ *
+ * clobbers: t0, t1, t9
+ */
+
+		.pushsection .bss
+hexbuf_addr:	.space 32
+		.popsection
+
+NESTED(printhex, 0, ra)
+	PTR_LA		t9, hexbuf_addr
+	sll		a1, a1, 1
+1:
+	subu		t0, a1, 1
+	sll		t0, t0, 2
+	LONG_SRLV	t0, a0, t0
+	andi		t0, t0, 0xf
+	li		t1, '0'
+	blt		t0, 10, 2f
+	li		t1, 'a'
+	addiu		t0, t0, -10
+2:
+	addu		t1, t1, t0
+	sb		t1, 0(t9)
+	PTR_ADDIU	t9, t9, 1
+	addiu		a1, a1, -1
+	bnez		a1, 1b
+	sb		zero, 0(t9)
+
+	move		a1, ra
+	PTR_LA		a0, hexbuf_addr
+	bal		printascii
+
+	jr		a1
+	END(printhex)
+
+NESTED(printhex1, 0, ra)
+	li		a1, 1
+	b		printhex
+	END(printhex1)
+
+NESTED(printhex2, 0, ra)
+	li		a1, 2
+	b		printhex
+	END(printhex2)
+
+NESTED(printhex4, 0, ra)
+	li		a1, 4
+	b		printhex
+	END(printhex4)
+
+#ifdef CONFIG_64BIT
+NESTED(printhex8, 0, ra)
+	li		a1, 8
+	b		printhex
+	END(printhex8)
+#endif
+
+NESTED(printhexl, 0, ra)
+	li		a1, PTRSIZE
+	b		printhex
+	END(printhexl)

-- 
2.34.1

[PATCH v3 3/9] MIPS: debug: Hook up DEBUG_LL with early printk

[Jiaxun Yang]

Output earlyprintk to low-level debug functions when it's
available.

DEBUG_LL takes priority over platform earlyprintk because
people must know what are they doing when they are trying
to enable DEBUG_LL.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug         |  2 +-
 arch/mips/kernel/early_printk.c | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 892e31804982..6ef42edc7d67 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -2,7 +2,7 @@
 
 config EARLY_PRINTK
 	bool "Early printk" if EXPERT
-	depends on SYS_HAS_EARLY_PRINTK
+	depends on SYS_HAS_EARLY_PRINTK || DEBUG_LL
 	default y
 	help
 	  This option enables special console drivers which allow the kernel
diff --git a/arch/mips/kernel/early_printk.c b/arch/mips/kernel/early_printk.c
index 4a1647ddfbd9..c3f3b0a930f0 100644
--- a/arch/mips/kernel/early_printk.c
+++ b/arch/mips/kernel/early_printk.c
@@ -14,6 +14,24 @@
 
 #include <asm/setup.h>
 
+#ifdef CONFIG_DEBUG_LL
+extern void printascii(const char *);
+
+static void early_console_write(struct console *con, const char *s, unsigned n)
+{
+	char buf[128];
+
+	while (n) {
+		unsigned int l = min(n, sizeof(buf)-1);
+
+		memcpy(buf, s, l);
+		buf[l] = 0;
+		s += l;
+		n -= l;
+		printascii(buf);
+	}
+}
+#else
 static void early_console_write(struct console *con, const char *s, unsigned n)
 {
 	while (n-- && *s) {
@@ -23,6 +41,7 @@ static void early_console_write(struct console *con, const char *s, unsigned n)
 		s++;
 	}
 }
+#endif
 
 static struct console early_console_prom = {
 	.name	= "early",

-- 
2.34.1

[PATCH v3 4/9] MIPS: debug: Provide an early exception vector for low-level debugging

[Jiaxun Yang]

This is helpful for debugging of early boot crash when exceptions
happens before trap_init(), or for debugging SMP bringup code.

It will install exception handler very early on kernel_entry by
setting ebase or copy itself to start of CKSEG0, and print off
exception vectors and other status registers like:

Low level exception: ffffffff8011e180

GlobalNumber: 0x00000000
EBase:    0xffffffff8011e000
Xcontext: 0x0000000000000000
Cause:    0x0000000c
Status:   0x14000082
EPC:      0xffffffff80d324e0
BadVAddr: 0x0000000000000000
BadInstr: 0xac000000

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug      |   9 ++
 arch/mips/kernel/Makefile    |   1 +
 arch/mips/kernel/debug-vec.S | 194 +++++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/head.S      |   4 +
 4 files changed, 208 insertions(+)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 6ef42edc7d67..323ad3ec643b 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -180,6 +180,15 @@ config DEBUG_LL
 	  this option should not be enabled for kernels that are intended to
 	  be portable.
 
+config DEBUG_LL_EXCEPT
+	bool "Kernel low-level debugging of exceptions"
+	depends on DEBUG_LL
+	help
+	  Say Y here to enable debugging prints for low-level exceptions.
+	  This is helpful if you are debugging a early boot crash when
+	  exceptions happens before trap_init(), or if you are debugging
+	  SMP bringup code.
+
 choice
 	prompt "Kernel low-level debugging port"
 	depends on DEBUG_LL
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index bfac35a64ae5..6641c3370e68 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -79,6 +79,7 @@ obj-$(CONFIG_MIPS32_N32)	+= scall64-n32.o signal_n32.o
 obj-$(CONFIG_MIPS32_O32)	+= scall64-o32.o signal_o32.o
 
 obj-$(CONFIG_DEBUG_LL)		+= debug.o
+obj-$(CONFIG_DEBUG_LL_EXCEPT)	+= debug-vec.o
 
 obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_PROC_FS)		+= proc.o
diff --git a/arch/mips/kernel/debug-vec.S b/arch/mips/kernel/debug-vec.S
new file mode 100644
index 000000000000..4530bf3d5b75
--- /dev/null
+++ b/arch/mips/kernel/debug-vec.S
@@ -0,0 +1,194 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@flygoat.com>
+ *  MIPS Low level exception vectors and handler
+ */
+
+#include <asm/addrspace.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/asmmacro.h>
+
+
+.balign 0x1000
+LEAF(debug_ll_vecs)
+	.set	push
+	.set	noreorder
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x80
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x100
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x180
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x200
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x280
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x300
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x380
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x400
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+.org	0x480
+	move	a0, zero
+	PTR_LA  t9, debug_ll_exception
+	jalr	t9
+	nop
+	b	.
+	nop
+
+	.set	pop
+END(debug_ll_vecs)
+
+
+/**
+ * debug_ll_exception() - dump relevant exception state to LL outputs
+ * @a0: pointer to NULL-terminated ASCII string naming the exception
+ *
+ * If a0 is NULL, it will print out exception vector number calculated
+ * from the ra insted. This is useful for debugging exceptions that
+ * happen before the exception handler is set up, or routed from BEV.
+ */
+LEAF(debug_ll_exception)
+	move		k0, ra
+	move		k1, a0
+	PTR_LA		t3, printascii
+
+	PTR_LA		a0, str_newline
+	jalr		t3  /* Call printascii */
+	PTR_LA		a0, str_exp
+	jalr		t3  /* Call printascii */
+	beqz		k1, 1f
+	move		a0, k1
+	jalr		t3  /* Call printascii */
+	b		2f
+1:
+	PTR_SRL		a0, k0, 7
+	PTR_SLL		a0, a0, 7
+	PTR_LA		t2, printhexl
+	jalr		t2
+2:
+	PTR_LA		a0, str_newline
+	jalr		t3  /* Call printascii */
+	PTR_LA		a0, str_newline
+	jalr		t3  /* Call printascii */
+
+#define DUMP_COP0_REG(reg, name, sz, _mfc0)		\
+	PTR_LA		a0, 8f;				\
+	jalr		t3;				\
+	_mfc0		a0, reg;			\
+	PTR_LA		t2, printhex##sz;		\
+	jalr		t2;				\
+	PTR_LA		a0, str_newline;		\
+	jalr		t3;				\
+	TEXT(name)
+
+#if defined(CONFIG_SMP) && defined(CONFIG_CPU_MIPSR6)
+	DUMP_COP0_REG(CP0_GLOBALNUMBER, "GlobalNumber: 0x", 4, mfc0)
+#endif
+#if MIPS_ISA_REV >= 2
+	DUMP_COP0_REG(CP0_EBASE,    "EBase:    0x", l, MFC0)
+#endif
+#ifdef CONFIG_64BIT
+	DUMP_COP0_REG(CP0_XCONTEXT, "Xcontext: 0x", 8, dmfc0)
+#else
+	DUMP_COP0_REG(CP0_CONTEXT,  "Context:  0x", 4, mfc0)
+#endif
+	DUMP_COP0_REG(CP0_CAUSE,    "Cause:    0x", 4, mfc0)
+	DUMP_COP0_REG(CP0_STATUS,   "Status:   0x", 4, mfc0)
+	DUMP_COP0_REG(CP0_EPC,      "EPC:      0x", l, MFC0)
+	DUMP_COP0_REG(CP0_BADVADDR, "BadVAddr: 0x", l, MFC0)
+#if MIPS_ISA_REV >= 6
+	DUMP_COP0_REG(CP0_BADINSTR, "BadInstr: 0x", 4, mfc0)
+#endif
+	PTR_LA		a0, str_newline
+	jalr		t3  /* Call printascii */
+	jr		k0
+	END(debug_ll_exception)
+
+.pushsection	.rodata.str
+str_exp: .asciiz "Low level exception: "
+str_newline: .asciiz "\r\n"
+.popsection
+
+NESTED(setup_debug_ll_exception, 0, ra)
+	PTR_LA		t0, debug_ll_vecs
+#if MIPS_ISA_REV >= 2
+	/* Set ebase to debug_ll_vecs */
+#if defined (CONFIG_64BIT) && !defined(KBUILD_64BIT_SYM32)
+	ori		t0, MIPS_EBASE_WG
+#endif
+	MTC0		t0, CP0_EBASE
+#else
+	/* Copy debug_ll_vecs to start of KSEG0 */
+	PTR_LI		t1, CKSEG0
+	PTR_ADDIU	t2, t0, 0x400 /* Only copy 0x400 as that is what reserved on old systems */
+copy_word:
+	PTR_LW		t3, 0(t0)
+	PTR_SW		t3, 0(t1)
+	PTR_ADDIU	t0, t0, PTRSIZE
+	PTR_ADDIU	t1, t1, PTRSIZE
+	PTR_BNE		t0, t2, copy_word
+#endif
+	/* Clear BEV bit in status register */
+	mfc0		t0, CP0_STATUS
+	and		t0, t0, ~ST0_BEV
+	mtc0		t0, CP0_STATUS
+	jr		ra
+	END(setup_debug_ll_exception)
diff --git a/arch/mips/kernel/head.S b/arch/mips/kernel/head.S
index b825ed4476c7..9be1c4ce6324 100644
--- a/arch/mips/kernel/head.S
+++ b/arch/mips/kernel/head.S
@@ -106,6 +106,10 @@ NESTED(kernel_entry, 16, sp)			# kernel entry point
 	LONG_S		a2, fw_arg2
 	LONG_S		a3, fw_arg3
 
+#ifdef CONFIG_DEBUG_LL_EXCEPT
+	jal		setup_debug_ll_exception
+#endif
+
 	MTC0		zero, CP0_CONTEXT	# clear context register
 #ifdef CONFIG_64BIT
 	MTC0		zero, CP0_XCONTEXT

-- 
2.34.1

[PATCH v3 5/9] MIPS: debug_ll: Add Kconfig symbols for some 8250 uarts

[Jiaxun Yang]

Define platform symbols for all 8250 style uart type supported
by zboot, plus Loongson-2K and boston.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug | 56 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 323ad3ec643b..3609d298a9eb 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -209,6 +209,54 @@ choice
 		  selecting one of the platform specific options below if
 		  you know the parameters for the port.
 
+	config DEBUG_BOSTON_UART
+		bool "Kernel low-level debugging messages via Boston UART"
+		depends on MIPS_GENERIC_KERNEL
+		select DEBUG_UART_8250
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on IMG Boston board.
+
+	config DEBUG_MALTA_UART
+		bool "Kernel low-level debugging messages via malta UART"
+		depends on MIPS_MALTA
+		select DEBUG_UART_8250
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on MTI malta board.
+
+	config DEBUG_AR71XX_UART
+		bool "Kernel low-level debugging messages via AR71XX UART"
+		depends on ATH79
+		select DEBUG_UART_8250
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on AR71xx based platforms.
+
+	config DEBUG_LOONGSON3_UART
+		bool "Kernel low-level debugging messages via Loongson-3 UART"
+		depends on MACH_LOONGSON64
+		select DEBUG_UART_8250
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on Loongson-3 systems.
+
+	config DEBUG_LOONGSON2K_UART
+		bool "Kernel low-level debugging messages via Loongson 2K UART"
+		depends on MACH_LOONGSON64
+		select DEBUG_UART_8250
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on Loongson-2K SoCs.
+
+	config DEBUG_INGENIC_UART
+		bool "Kernel low-level debugging messages via Ingenic UART"
+		depends on MACH_INGENIC_SOC
+		select DEBUG_UART_8250
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on uart0 of Ingenic SoCs.
+
 endchoice
 
 config DEBUG_LL_INCLUDE
@@ -239,6 +287,12 @@ config DEBUG_UART_FLOW_CONTROL
 config DEBUG_UART_PHYS
 	hex "Physical base address of debug UART"
 	depends on DEBUG_LL_UART
+	default 0x17ffe000 if DEBUG_BOSTON_UART
+	default 0x1fd003f8 if DEBUG_MALTA_UART
+	default 0x18020000 if DEBUG_AR71XX_UART
+	default 0x1fd003f8 if DEBUG_LOONGSON3_UART
+	default 0x1fe00000 if DEBUG_LOONGSON2K_UART
+	default 0x10030000 if DEBUG_INGENIC_UART
 	help
 	  This is the physical base address of the debug UART. It must be
 	  accessible from unmapped kernel space (i.e. KSEG1 for 32bit kernels
@@ -247,6 +301,8 @@ config DEBUG_UART_PHYS
 config DEBUG_UART_8250_SHIFT
 	int "Register offset shift for the 8250 debug UART"
 	depends on DEBUG_LL_UART_8250 || DEBUG_UART_8250
+	default 1 if DEBUG_MALTA_UART || DEBUG_LOONGSON3_UART || \
+		DEBUG_LOONGSON2K_UART
 	default 2
 
 config DEBUG_UART_8250_WIDTH

-- 
2.34.1

[PATCH v3 6/9] MIPS: debug_ll: Implement support for Alchemy uarts

[Jiaxun Yang]

Alchemy uart is a 8250 derivative that requires some special care
on barriers and readys, also they have a wired register layout.

Implement it as a special include.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug           | 10 +++++++++
 arch/mips/include/debug/alchemy.S | 46 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 3609d298a9eb..aef116058654 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -257,11 +257,20 @@ choice
 		  Say Y here if you want kernel low-level debugging support
 		  on uart0 of Ingenic SoCs.
 
+	config DEBUG_ALCHEMY_UART
+		bool "Kernel low-level debugging messages via Alchemy UART"
+		depends on MIPS_ALCHEMY
+		select DEBUG_LL_UART
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on uart of alchemy SoCs.
+
 endchoice
 
 config DEBUG_LL_INCLUDE
 	string
 	default "debug/8250.S" if DEBUG_LL_UART_8250 || DEBUG_UART_8250
+	default "debug/alchemy.S" if DEBUG_ALCHEMY_UART
 	default "debug/uhi.S" if DEBUG_MIPS_UHI
 	default "debug-macro.S"
 
@@ -293,6 +302,7 @@ config DEBUG_UART_PHYS
 	default 0x1fd003f8 if DEBUG_LOONGSON3_UART
 	default 0x1fe00000 if DEBUG_LOONGSON2K_UART
 	default 0x10030000 if DEBUG_INGENIC_UART
+	default 0x11100000 if DEBUG_ALCHEMY_UART
 	help
 	  This is the physical base address of the debug UART. It must be
 	  accessible from unmapped kernel space (i.e. KSEG1 for 32bit kernels
diff --git a/arch/mips/include/debug/alchemy.S b/arch/mips/include/debug/alchemy.S
new file mode 100644
index 000000000000..933efc6e828c
--- /dev/null
+++ b/arch/mips/include/debug/alchemy.S
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@flygoat.com>
+ * MIPS Low level debug include file for Au1xxx UART
+ * Dereived from drivers/tty/serial/8250/8250_rt288x.c
+ */
+
+#include <asm/addrspace.h>
+#include <asm/asm.h>
+#include <linux/serial_reg.h>
+
+#define DEBUG_LL_UART
+
+#define UART_BASE	CKSEG1ADDR(CONFIG_DEBUG_UART_PHYS)
+
+#define UART_TX_OFS	(1 << 2)
+#define UART_LSR_OFS	(7 << 2)
+
+# define UART_L		lw
+# define UART_S		sw
+
+		.macro	addruart,rd,rx
+		PTR_LA	\rd, UART_BASE
+		.endm
+
+		.macro	senduart,rd,rx
+		UART_S   \rd, UART_TX_OFS(\rx)
+		sync	/* wmb */
+		.endm
+
+		.macro	busyuart,rd,rx
+1002:
+		UART_L	\rd, UART_LSR_OFS(\rx)
+		andi	\rd, \rd, (UART_LSR_TEMT | UART_LSR_THRE)
+		xori	\rd, (UART_LSR_TEMT | UART_LSR_THRE)
+		sync	/* cpu_relax */
+		bnez	\rd, 1002b
+		.endm
+
+		.macro	waituarttxrdy,rd,rx
+		busyuart \rd, \rx
+		.endm
+
+		/* Au1xxx has no MSR */
+		.macro	waituartcts,rd,rx
+		.endm

-- 
2.34.1

[PATCH v3 7/9] MIPS: debug_ll: Implement support for AR933X uarts

[Jiaxun Yang]

Implement support for AR933X uarts which has it's own register
definition.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug          |  9 +++++++++
 arch/mips/include/debug/ar933x.S | 41 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index aef116058654..a6687c503c34 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -265,6 +265,14 @@ choice
 		  Say Y here if you want kernel low-level debugging support
 		  on uart of alchemy SoCs.
 
+	config DEBUG_AR933X_UART
+		bool "Kernel low-level debugging messages via Alchemy UART"
+		depends on MIPS_ALCHEMY
+		select DEBUG_LL_UART
+		help
+		  Say Y here if you want kernel low-level debugging support
+		  on uart of AR933X SoCs.
+
 endchoice
 
 config DEBUG_LL_INCLUDE
@@ -303,6 +311,7 @@ config DEBUG_UART_PHYS
 	default 0x1fe00000 if DEBUG_LOONGSON2K_UART
 	default 0x10030000 if DEBUG_INGENIC_UART
 	default 0x11100000 if DEBUG_ALCHEMY_UART
+	default 0x18020000 if DEBUG_AR933X_UART
 	help
 	  This is the physical base address of the debug UART. It must be
 	  accessible from unmapped kernel space (i.e. KSEG1 for 32bit kernels
diff --git a/arch/mips/include/debug/ar933x.S b/arch/mips/include/debug/ar933x.S
new file mode 100644
index 000000000000..1a0449082080
--- /dev/null
+++ b/arch/mips/include/debug/ar933x.S
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023, Jiaxun Yang <jiaxun.yang@flygoat.com>
+ * MIPS Low level debug include file for ar933x UART
+ */
+
+#include <asm/addrspace.h>
+#include <asm/asm.h>
+#include <asm/mach-ath79/ar933x_uart.h>
+
+#define DEBUG_LL_UART
+
+#define UART_BASE	CKSEG1ADDR(CONFIG_DEBUG_UART_PHYS)
+
+# define UART_L		lw
+# define UART_S		sw
+
+		.macro	addruart,rd,rx
+		PTR_LA	\rd, UART_BASE
+		.endm
+
+		.macro	senduart,rd,rx
+		UART_S   \rd, AR933X_UART_DATA_REG(\rx)
+		.endm
+
+        /* CTS and RDY are handled by AR933X_UART_DATA_TX_CSR as well */
+		.macro	busyuart,rd,rx
+1002:
+		UART_L	\rd, AR933X_UART_DATA_REG(\rx)
+		andi	\rd, \rd, (AR933X_UART_DATA_TX_CSR)
+		xori	\rd, (AR933X_UART_DATA_TX_CSR)
+		bnez	\rd, 1002b
+		.endm
+
+		.macro	waituarttxrdy,rd,rx
+        busyuart \rd, \rx
+		.endm
+
+		.macro	waituartcts,rd,rx
+        busyuart \rd, \rx
+		.endm

-- 
2.34.1

[PATCH v3 8/9] MIPS: zboot: Convert to use debug_ll facilities

[Jiaxun Yang]

Since now debug_ll facilities can cover all platforms supported
by zboot debug print, and it provides extra capability on debugging
exceptions, switch zboot to use those facilities.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig                        | 12 ++------
 arch/mips/Kconfig.debug                  | 46 +++++++++++++-----------------
 arch/mips/boot/compressed/Makefile       |  9 ++----
 arch/mips/boot/compressed/dbg.c          | 39 -------------------------
 arch/mips/boot/compressed/debug-vec.S    |  3 ++
 arch/mips/boot/compressed/debug.S        |  3 ++
 arch/mips/boot/compressed/decompress.h   |  8 +++---
 arch/mips/boot/compressed/head.S         |  6 ++++
 arch/mips/boot/compressed/uart-16550.c   | 49 --------------------------------
 arch/mips/boot/compressed/uart-alchemy.c |  9 ------
 arch/mips/boot/compressed/uart-ath79.c   |  2 --
 arch/mips/boot/compressed/uart-prom.c    |  9 ------
 12 files changed, 39 insertions(+), 156 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 06ef440d16ce..6729bf1d158d 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -240,7 +240,7 @@ config ATH79
 	select SYS_SUPPORTS_32BIT_KERNEL
 	select SYS_SUPPORTS_BIG_ENDIAN
 	select SYS_SUPPORTS_MIPS16
-	select SYS_SUPPORTS_ZBOOT_UART_PROM
+	select SYS_SUPPORTS_ZBOOT
 	select USE_OF
 	select USB_EHCI_ROOT_HUB_TT if USB_EHCI_HCD_PLATFORM
 	help
@@ -422,7 +422,7 @@ config MACH_INGENIC_SOC
 	select MIPS_GENERIC
 	select MACH_INGENIC
 	select MACH_GENERIC_CORE
-	select SYS_SUPPORTS_ZBOOT_UART16550
+	select SYS_SUPPORTS_ZBOOT
 	select CPU_SUPPORTS_CPUFREQ
 	select MIPS_EXTERNAL_TIMER
 
@@ -1792,14 +1792,6 @@ config SYS_SUPPORTS_ZBOOT
 	select HAVE_KERNEL_XZ
 	select HAVE_KERNEL_ZSTD
 
-config SYS_SUPPORTS_ZBOOT_UART16550
-	bool
-	select SYS_SUPPORTS_ZBOOT
-
-config SYS_SUPPORTS_ZBOOT_UART_PROM
-	bool
-	select SYS_SUPPORTS_ZBOOT
-
 config CPU_LOONGSON2EF
 	bool
 	select CPU_SUPPORTS_32BIT_KERNEL
diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index a6687c503c34..0ce6d24d05b3 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -79,33 +79,6 @@ config SB1XXX_CORELIS
 	  Select compile flags that produce code that can be processed by the
 	  Corelis mksym utility and UDB Emulator.
 
-config DEBUG_ZBOOT
-	bool "Enable compressed kernel support debugging"
-	depends on DEBUG_KERNEL && SYS_SUPPORTS_ZBOOT
-	default n
-	help
-	  If you want to add compressed kernel support to a new board, and the
-	  board supports uart16550 compatible serial port, please select
-	  SYS_SUPPORTS_ZBOOT_UART16550 for your board and enable this option to
-	  debug it.
-
-	  If your board doesn't support uart16550 compatible serial port, you
-	  can try to select SYS_SUPPORTS_ZBOOT and use the other methods to
-	  debug it. for example, add a new serial port support just as
-	  arch/mips/boot/compressed/uart-16550.c does.
-
-	  After the compressed kernel support works, please disable this option
-	  to reduce the kernel image size and speed up the booting procedure a
-	  little.
-
-config ZBOOT_INGENIC_UART
-	int "UART to use for compressed kernel debugging"
-	depends on DEBUG_ZBOOT && MACH_INGENIC_SOC
-	default 0
-	range 0 4
-	help
-	  Specify the UART that should be used for compressed kernel debugging.
-
 config SPINLOCK_TEST
 	bool "Enable spinlock timing tests in debugfs"
 	depends on DEBUG_FS
@@ -328,3 +301,22 @@ config DEBUG_UART_8250_WIDTH
 	int "Register width for the 8250 debug UART"
 	depends on DEBUG_LL_UART_8250 || DEBUG_UART_8250
 	default 1
+
+config DEBUG_ZBOOT
+	bool "Enable compressed kernel debugging via DEBUG_LL output"
+	depends on DEBUG_LL && SYS_SUPPORTS_ZBOOT
+	help
+	  Say Y here if you want to enable debugging of a compressed kernel
+	  via the DEBUG_LL output.  This is useful if you are debugging
+	  decompressor issues.
+
+	  If unsure, say N.
+
+config DEBUG_ZBOOT_EXCEPT
+	bool "Enable compressed kernel debugging of exceptions"
+	depends on DEBUG_ZBOOT
+	help
+	  Say Y here if you want to enable debugging of exceptions happen
+	  during decompression of a compressed kernel via the DEBUG_LL output.
+
+	  If unsure, say N.
diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
index 6cc28173bee8..78c65db8dd04 100644
--- a/arch/mips/boot/compressed/Makefile
+++ b/arch/mips/boot/compressed/Makefile
@@ -43,13 +43,8 @@ KCSAN_SANITIZE			:= n
 # decompressor objects (linked with vmlinuz)
 vmlinuzobjs-y := $(obj)/head.o $(obj)/decompress.o $(obj)/string.o $(obj)/bswapsi.o
 
-ifdef CONFIG_DEBUG_ZBOOT
-vmlinuzobjs-$(CONFIG_DEBUG_ZBOOT)		   += $(obj)/dbg.o
-vmlinuzobjs-$(CONFIG_SYS_SUPPORTS_ZBOOT_UART16550) += $(obj)/uart-16550.o
-vmlinuzobjs-$(CONFIG_SYS_SUPPORTS_ZBOOT_UART_PROM) += $(obj)/uart-prom.o
-vmlinuzobjs-$(CONFIG_MIPS_ALCHEMY)		   += $(obj)/uart-alchemy.o
-vmlinuzobjs-$(CONFIG_ATH79)			   += $(obj)/uart-ath79.o
-endif
+vmlinuzobjs-$(CONFIG_DEBUG_ZBOOT)		+= $(obj)/debug.o
+vmlinuzobjs-$(CONFIG_DEBUG_ZBOOT_EXCEPT)	+= $(obj)/debug-vec.o
 
 vmlinuzobjs-$(CONFIG_KERNEL_XZ) += $(obj)/ashldi3.o
 
diff --git a/arch/mips/boot/compressed/dbg.c b/arch/mips/boot/compressed/dbg.c
deleted file mode 100644
index 95405292accd..000000000000
--- a/arch/mips/boot/compressed/dbg.c
+++ /dev/null
@@ -1,39 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * MIPS-specific debug support for pre-boot environment
- *
- * NOTE: putc() is board specific, if your board have a 16550 compatible uart,
- * please select SYS_SUPPORTS_ZBOOT_UART16550 for your machine. otherwise, you
- * need to implement your own putc().
- */
-#include <linux/compiler.h>
-#include <linux/types.h>
-
-#include "decompress.h"
-
-void __weak putc(char c)
-{
-}
-
-void puts(const char *s)
-{
-	char c;
-	while ((c = *s++) != '\0') {
-		putc(c);
-		if (c == '\n')
-			putc('\r');
-	}
-}
-
-void puthex(unsigned long long val)
-{
-
-	unsigned char buf[10];
-	int i;
-	for (i = 7; i >= 0; i--) {
-		buf[i] = "0123456789ABCDEF"[val & 0x0F];
-		val >>= 4;
-	}
-	buf[8] = '\0';
-	puts(buf);
-}
diff --git a/arch/mips/boot/compressed/debug-vec.S b/arch/mips/boot/compressed/debug-vec.S
new file mode 100644
index 000000000000..e7bedb183da8
--- /dev/null
+++ b/arch/mips/boot/compressed/debug-vec.S
@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "../../kernel/debug-vec.S"
diff --git a/arch/mips/boot/compressed/debug.S b/arch/mips/boot/compressed/debug.S
new file mode 100644
index 000000000000..0cf3da958f7e
--- /dev/null
+++ b/arch/mips/boot/compressed/debug.S
@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "../../kernel/debug.S"
diff --git a/arch/mips/boot/compressed/decompress.h b/arch/mips/boot/compressed/decompress.h
index 073b64593b3d..e375d50c71a0 100644
--- a/arch/mips/boot/compressed/decompress.h
+++ b/arch/mips/boot/compressed/decompress.h
@@ -7,11 +7,11 @@ extern unsigned char __image_begin[], __image_end[];
 
 /* debug interfaces  */
 #ifdef CONFIG_DEBUG_ZBOOT
-extern void putc(char c);
-extern void puts(const char *s);
-extern void puthex(unsigned long long val);
+extern void printascii(const char *s);
+extern void printhexl(unsigned long val);
+#define puts(s) printascii(s)
+#define puthex(val) printhexl(val)
 #else
-#define putc(s) do {} while (0)
 #define puts(s) do {} while (0)
 #define puthex(val) do {} while (0)
 #endif
diff --git a/arch/mips/boot/compressed/head.S b/arch/mips/boot/compressed/head.S
index d237a834b85e..b05e9591d3af 100644
--- a/arch/mips/boot/compressed/head.S
+++ b/arch/mips/boot/compressed/head.S
@@ -22,6 +22,12 @@
 	move	s2, a2
 	move	s3, a3
 
+#ifdef CONFIG_DEBUG_ZBOOT_EXCEP
+	/* Set up the exception vector */
+	PTR_LA	t9, setup_debug_ll_exception
+	jalr	t9
+#endif
+
 	/* Clear BSS */
 	PTR_LA	a0, _edata
 	PTR_LA	a2, _end
diff --git a/arch/mips/boot/compressed/uart-16550.c b/arch/mips/boot/compressed/uart-16550.c
deleted file mode 100644
index db618e72a0c4..000000000000
--- a/arch/mips/boot/compressed/uart-16550.c
+++ /dev/null
@@ -1,49 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * 16550 compatible uart based serial debug support for zboot
- */
-
-#include <linux/types.h>
-#include <linux/serial_reg.h>
-
-#include <asm/addrspace.h>
-
-#include "decompress.h"
-
-#if defined(CONFIG_MACH_LOONGSON64) || defined(CONFIG_MIPS_MALTA)
-#define UART_BASE 0x1fd003f8
-#define PORT(offset) (CKSEG1ADDR(UART_BASE) + (offset))
-#endif
-
-#ifdef CONFIG_MACH_INGENIC
-#define INGENIC_UART_BASE_ADDR	(0x10030000 + 0x1000 * CONFIG_ZBOOT_INGENIC_UART)
-#define PORT(offset) (CKSEG1ADDR(INGENIC_UART_BASE_ADDR) + (4 * offset))
-#endif
-
-#ifndef IOTYPE
-#define IOTYPE char
-#endif
-
-#ifndef PORT
-#error please define the serial port address for your own machine
-#endif
-
-static inline unsigned int serial_in(int offset)
-{
-	return *((volatile IOTYPE *)PORT(offset)) & 0xFF;
-}
-
-static inline void serial_out(int offset, int value)
-{
-	*((volatile IOTYPE *)PORT(offset)) = value & 0xFF;
-}
-
-void putc(char c)
-{
-	int timeout = 1000000;
-
-	while (((serial_in(UART_LSR) & UART_LSR_THRE) == 0) && (timeout-- > 0))
-		;
-
-	serial_out(UART_TX, c);
-}
diff --git a/arch/mips/boot/compressed/uart-alchemy.c b/arch/mips/boot/compressed/uart-alchemy.c
deleted file mode 100644
index 003967c084b3..000000000000
--- a/arch/mips/boot/compressed/uart-alchemy.c
+++ /dev/null
@@ -1,9 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <asm/mach-au1x00/au1000.h>
-
-#include "decompress.h"
-
-void putc(char c)
-{
-	alchemy_uart_putchar(AU1000_UART0_PHYS_ADDR, c);
-}
diff --git a/arch/mips/boot/compressed/uart-ath79.c b/arch/mips/boot/compressed/uart-ath79.c
deleted file mode 100644
index d686820921be..000000000000
--- a/arch/mips/boot/compressed/uart-ath79.c
+++ /dev/null
@@ -1,2 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-#include "../../ath79/early_printk.c"
diff --git a/arch/mips/boot/compressed/uart-prom.c b/arch/mips/boot/compressed/uart-prom.c
deleted file mode 100644
index 5fa3b9945333..000000000000
--- a/arch/mips/boot/compressed/uart-prom.c
+++ /dev/null
@@ -1,9 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <asm/setup.h>
-
-#include "decompress.h"
-
-void putc(char c)
-{
-	prom_putchar(c);
-}

-- 
2.34.1

[PATCH v3 9/9] MIPS: CPS: Convert to use debug_ll facilities

[Jiaxun Yang]

debug_ll replaced CPS's custom NS16550 printing functions
for dump early SMP bring-up exceptions.

This will enable CPS debugging on more platforms and also
reduce code duplication.

All exception name strings are prefixed with CPS to help
identification with regular low-level interrupts.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 arch/mips/Kconfig.debug    | 52 +++++++++-------------------------------------
 arch/mips/kernel/Makefile  |  1 -
 arch/mips/kernel/cps-vec.S | 16 +++++++-------
 3 files changed, 18 insertions(+), 51 deletions(-)

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 0ce6d24d05b3..caba00cd8a33 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -96,48 +96,6 @@ config SCACHE_DEBUGFS
 
 	  If unsure, say N.
 
-menuconfig MIPS_CPS_NS16550_BOOL
-	bool "CPS SMP NS16550 UART output"
-	depends on MIPS_CPS
-	help
-	  Output debug information via an ns16550 compatible UART if exceptions
-	  occur early in the boot process of a secondary core.
-
-if MIPS_CPS_NS16550_BOOL
-
-config MIPS_CPS_NS16550
-	def_bool MIPS_CPS_NS16550_BASE != 0
-
-config MIPS_CPS_NS16550_BASE
-	hex "UART Base Address"
-	default 0x1b0003f8 if MIPS_MALTA
-	default 0
-	help
-	  The base address of the ns16550 compatible UART on which to output
-	  debug information from the early stages of core startup.
-
-	  This is only used if non-zero.
-
-config MIPS_CPS_NS16550_SHIFT
-	int "UART Register Shift"
-	default 0
-	help
-	  The number of bits to shift ns16550 register indices by in order to
-	  form their addresses. That is, log base 2 of the span between
-	  adjacent ns16550 registers in the system.
-
-config MIPS_CPS_NS16550_WIDTH
-	int "UART Register Width"
-	default 1
-	help
-	  ns16550 registers width. UART registers IO access methods will be
-	  selected in accordance with this parameter. By setting it to 1, 2 or
-	  4 UART registers will be accessed by means of lb/sb, lh/sh or lw/sw
-	  instructions respectively. Any value not from that set activates
-	  lb/sb instructions.
-
-endif # MIPS_CPS_NS16550_BOOL
-
 # These options are only for real kernel hackers who want to get their hands dirty.
 config DEBUG_LL
 	bool "Kernel low-level debugging functions (read help!)"
@@ -320,3 +278,13 @@ config DEBUG_ZBOOT_EXCEPT
 	  during decompression of a compressed kernel via the DEBUG_LL output.
 
 	  If unsure, say N.
+
+config DEBUG_CPS_EXCEPT
+	bool "Enable kernel debugging of Coherent Processing System exceptions"
+	depends on MIPS_CPS && DEBUG_LL_EXCEPT
+	help
+	  Say Y here if you want to enable debugging of exceptions happen
+	  during SMP bring-up stages on processors witn MIPS Coherent Processing
+	  System support.
+
+	  If unsure, say N.
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 6641c3370e68..94325c02cae2 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -59,7 +59,6 @@ obj-$(CONFIG_MIPS_MT)		+= mips-mt.o
 obj-$(CONFIG_MIPS_MT_FPAFF)	+= mips-mt-fpaff.o
 obj-$(CONFIG_MIPS_MT_SMP)	+= smp-mt.o
 obj-$(CONFIG_MIPS_CPS)		+= smp-cps.o cps-vec.o
-obj-$(CONFIG_MIPS_CPS_NS16550)	+= cps-vec-ns16550.o
 obj-$(CONFIG_MIPS_SPRAM)	+= spram.o
 
 obj-$(CONFIG_MIPS_VPE_LOADER)	+= vpe.o
diff --git a/arch/mips/kernel/cps-vec.S b/arch/mips/kernel/cps-vec.S
index f876309130ad..49d682b3b49a 100644
--- a/arch/mips/kernel/cps-vec.S
+++ b/arch/mips/kernel/cps-vec.S
@@ -33,15 +33,15 @@
 # define STATUS_BITDEPS		0
 #endif
 
-#ifdef CONFIG_MIPS_CPS_NS16550
+#ifdef CONFIG_DEBUG_CPS_EXCEPT
 
 #define DUMP_EXCEP(name)		\
 	PTR_LA	a0, 8f;			\
-	jal	mips_cps_bev_dump;	\
+	jal	debug_ll_exception;	\
 	 nop;				\
 	TEXT(name)
 
-#else /* !CONFIG_MIPS_CPS_NS16550 */
+#else /* !CONFIG_DEBUG_CPS_EXCEPT */
 
 #define DUMP_EXCEP(name)
 
@@ -154,31 +154,31 @@ LEAF(mips_cps_core_boot)
 
 	__INIT
 LEAF(excep_tlbfill)
-	DUMP_EXCEP("TLB Fill")
+	DUMP_EXCEP("CPS - TLB Fill")
 	b	.
 	 nop
 	END(excep_tlbfill)
 
 LEAF(excep_xtlbfill)
-	DUMP_EXCEP("XTLB Fill")
+	DUMP_EXCEP("CPS - XTLB Fill")
 	b	.
 	 nop
 	END(excep_xtlbfill)
 
 LEAF(excep_cache)
-	DUMP_EXCEP("Cache")
+	DUMP_EXCEP("CPS - Cache")
 	b	.
 	 nop
 	END(excep_cache)
 
 LEAF(excep_genex)
-	DUMP_EXCEP("General")
+	DUMP_EXCEP("CPS - General")
 	b	.
 	 nop
 	END(excep_genex)
 
 LEAF(excep_intex)
-	DUMP_EXCEP("Interrupt")
+	DUMP_EXCEP("CPS - Interrupt")
 	b	.
 	 nop
 	END(excep_intex)

-- 
2.34.1

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Jiaxun Yang]

在2024年5月2日五月 上午10:59，Jiaxun Yang写道：
> Hi all,
>
> This is a attempt to bring all low-level debugging print functions
> together and provide a arm-like low-level debugging interface and
> a further capability to debug early exceptions.
>
> This patch elimiate platform specific early_printk, zboot printing
> functions and cps-vec-ns16550 by newly introduced debug_ll.
>
> Hope you'll find them handy :-)
>
> Happy hacking!
>
> Thanks
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

A gentle ping.

Our reviewing capacity is quite low recently, hope everything is fine
with Thomas.

Thanks
[...]
- Jiaxun

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Jiaxun Yang]

在2024年5月15日五月 下午10:28，Jiaxun Yang写道：
[...]
>
> A gentle ping.
>
> Our reviewing capacity is quite low recently, hope everything is fine
> with Thomas.

Another gentle-ish ping after 6.10 merge window.

This series has been floating here for so long, if I missed the merge
window, I think I deserve a notice.

Thanks
>
> Thanks
> [...]
> - Jiaxun

-- 
- Jiaxun

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Thomas Bogendoerfer]

On Wed, May 22, 2024 at 08:15:22AM +0100, Jiaxun Yang wrote:
> 
> 
> 在2024年5月15日五月 下午10:28，Jiaxun Yang写道：
> [...]
> >
> > A gentle ping.
> >
> > Our reviewing capacity is quite low recently, hope everything is fine
> > with Thomas.
> 
> Another gentle-ish ping after 6.10 merge window.
> 
> This series has been floating here for so long, if I missed the merge
> window, I think I deserve a notice.

hmmm, I thought I was clear enough on version 1 of this series.

I don't want an additional printk like debug interface, There is
prom_putchar() and early printk console, which always got me past
any boot issue.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Jiaxun Yang]

在2024年5月22日五月 上午9:03，Thomas Bogendoerfer写道：
[...]
>
> hmmm, I thought I was clear enough on version 1 of this series.
>
> I don't want an additional printk like debug interface, There is
> prom_putchar() and early printk console, which always got me past
> any boot issue.

So it's not an additional printk like debug interface, it actually
merged 3 existing debug interfaces, the first being zboot's assembly
print routines, the second being CPS's assembly print routines, the
third being some platform specific early printk. I think they are
all essential for debugging early faults, for zboot that's the only
way to print something at decompressing stage, for CPS as other cores
are booting in non-coherent state we can't safely use any kernel
functions, for early_printk that can help us *reduce* the amount
of early printk code by just adding UART base to config.

The only thing being added is the ability to debug very early exception,
even that is partially ported from existing CPS assembly debugging routines.

Please let me know your thoughts.

Thanks
>
> Thomas.
>
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]

-- 
- Jiaxun

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Jiaxun Yang]

在2024年5月22日五月 上午9:28，Jiaxun Yang写道：
> 在2024年5月22日五月 上午9:03，Thomas Bogendoerfer写道：
> [...]
>>
>> hmmm, I thought I was clear enough on version 1 of this series.
>>
>> I don't want an additional printk like debug interface, There is
>> prom_putchar() and early printk console, which always got me past
>> any boot issue.
>
> So it's not an additional printk like debug interface, it actually
> merged 3 existing debug interfaces, the first being zboot's assembly
> print routines, the second being CPS's assembly print routines, the
> third being some platform specific early printk. I think they are
> all essential for debugging early faults, for zboot that's the only
> way to print something at decompressing stage, for CPS as other cores
> are booting in non-coherent state we can't safely use any kernel
> functions, for early_printk that can help us *reduce* the amount
> of early printk code by just adding UART base to config.
>
> The only thing being added is the ability to debug very early exception,
> even that is partially ported from existing CPS assembly debugging routines.
>
> Please let me know your thoughts.

That being said, have you noticed that prom_putchar and early_printk is
a non-extant on generic mach, ingenic, ralink etc? That's because we
really don't want to introduce any platform specific UART code for
early debugging on new platforms. With DEBUG_LL introduced by Arm it's
only a Kconfig option to do the trick.

I've got review tags in PATCH v2, that means not only me feeling that
this series is reasonable.

arm64 / riscv doesn't need that because they are well standardized
and it's almost guaranteed that kernel can boot into earlycon without
much drama. For MIPS that's not the case, there are too many things that
may go wrong, from zboot decompressor to cpu-probe and memblock. We really
lacks a way to debug things early, we need something that is available
at 1st instruction at kernel entry. Furthermore, many MIPS processors
don't come with JTAG or alike debugging support, that makes debugging
even harder, there is no way to debug an early exception if your firmware
doesn't handle it. That's all the motivation behind the series.

Besides, I think our communication needs to be improved. At PATCH v1
you made your point in reply, that's fair. So I also replied twice for
clarification. I heard nothing back, so I assume you want to see how
would it develop to address your concern. Then I posted PATCH v2 and
v3 to further improve the series, after that I pinged twice on PATCH v3.

That's in a 6-month timeframe with multiple transactions, you need to
inform us your intention, even if it's a NAK or you don't want to engage
on this topic further.

Quoting the maintainer handbook [1]: "If the review process or validation
for a particular change will take longer than the expected review timeline
for the subsystem, maintainer should reply to the submission indicating
that the work is being done, and when to expect full results." Radio silence
won't help anything, it's wasting time for both of us. Please, give a
shout if it's possible.

I can see some other series being slipped away this way, like I6500
multi-cluster patch, which is sent even earlier and respined many times
over. I can recall Mobileye series had a hard time on getting your
attention, luckily we went through it.

Quoting the maintainer handbook [1]: "Nonetheless when the work does
arrive (in form of patches which need review, user bug reports etc.)
it has to be acted upon promptly.". I understand Linux/MIPS is not
your day job, also you need to take breaks or go on holidays. Sometimes
you may burn out from your maintainer duties. That's fine, we are all
human beings. I'm not expecting a 1-week SLA or something, but 6 months
or longer to expect an action is appalling to me.

I'd strongly recommend you to look for a secondary maintainer, as mentioned
in maintainer handbook [1]: "Modern best practices dictate that there should
be at least two maintainers for any piece of code, no matter how trivial".
I understand you reject the idea once when Paul handed maintainership to
you, but there are clear evidences to show that something needs to be done.
You might need a hand on handling stuff promptly and understanding some
modern MIPS stuff.

I have many, many tiny improvements to MIPS kernel locally. Furthermore,
I do bring-up for both new and ancient MIPS systems. I never got a chance
to send them out because I want you prioritise on those fundamental series.

Apologise for potential aggressive tone in this email. I just can't clam
down when I think back about your reply, and I think we really need to
talk about it.

Thanks

[1]: https://docs.kernel.org/maintainer/feature-and-driver-maintainers.html
-- 
- Jiaxun

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Maciej W. Rozycki]

On Wed, 22 May 2024, Jiaxun Yang wrote:

> That being said, have you noticed that prom_putchar and early_printk is
> a non-extant on generic mach, ingenic, ralink etc? That's because we
> really don't want to introduce any platform specific UART code for
> early debugging on new platforms. With DEBUG_LL introduced by Arm it's
> only a Kconfig option to do the trick.

 IMHO that is however the logical thing to do.  And then you need no magic 
options to fiddle with and say a distribution kernel will dump whatever it 
has to say if something wrong has happened early on.

 IOW just wire `prom_putchar' as required, using C code preferably.  NB 
YAMON does have a `print' entry point for console output, so for the Malta 
platform you can trivially use just that, no need for messy ad hoc 8250 
code.

 As to intercepting exceptions, it depends.  Again YAMON does handle that 
and dumps the register state, so with the Malta you get the information 
required.  For less capable ones it might make sense, but it ISTM like a 
candidate for an independent change, and then again I fail to see why the 
handler has to be written in the assembly language rather than C.

  Maciej

Re: [PATCH v3 0/9] MIPS: Unify low-level debugging functionalities

[Jiaxun Yang]

在2024年5月26日五月 下午1:44，Maciej W. Rozycki写道：
> On Wed, 22 May 2024, Jiaxun Yang wrote:
>
>> That being said, have you noticed that prom_putchar and early_printk is
>> a non-extant on generic mach, ingenic, ralink etc? That's because we
>> really don't want to introduce any platform specific UART code for
>> early debugging on new platforms. With DEBUG_LL introduced by Arm it's
>> only a Kconfig option to do the trick.

Hi Maciej,

Thanks for your thoughts, my two cents below.
>
>  IMHO that is however the logical thing to do.  And then you need no magic 
> options to fiddle with and say a distribution kernel will dump whatever it 
> has to say if something wrong has happened early on.

This is a strict debug only options, we are not expecting any distribution
kernel to enable it. It has made itself explicit that no production device
should enable it.

Setting UART address for debug console by developers know what are they
doing is a proven approach among multiple places in multiple projects.

For kernel we have general earlycon cmdline option that would take MMIO
base address, Arm's DEBUG_LL had taken a similar approach and U-Boot have
CONFIG_DEBUG_UART_BASE, even our old zboot debug print code is taking such
approach.

It takes a balance between platform dependent code addition and bring-up
debugging capability. I fail to see why does it suddenly become an undesired
thing here.

>
>  IOW just wire `prom_putchar' as required, using C code preferably.  NB 
> YAMON does have a `print' entry point for console output, so for the Malta 
> platform you can trivially use just that, no need for messy ad hoc 8250 
> code.

Sadly for the majority of modern MIPS devices are dominated by U-Boot or
vendor's simple loader. In most cases, runtime APIs are not provided by
default. Even if it's enabled, there are still a couple of reasons preventing
it to be utilized properly. U-Boot relies on global pointer stored in K0 to
save global runtime data, kernel will clobber it very early and makes U-Boot
non-functional. On devices with limited memory, it's easy to get U-Boot memory
being clobbered by kernel and render U-Boot's runtime useless anyway.

That's why many new-ish platforms such as lantiq brings it's own UART
implementations for prom_putchar.

However, for generic platform implementing prom_putchar means we need to
introduce platform dependent code, which we had to pay all the price to
avoid. We have many in-tree and out-of tree generic platform users who
don't need to add any single line of code to bring up their platform,
thanks to DeviceTree, but they still need something to help with debugging
bring up process when devicetree went wrong or early panics.

>
>  As to intercepting exceptions, it depends.  Again YAMON does handle that 
> and dumps the register state, so with the Malta you get the information 
> required.  For less capable ones it might make sense, but it ISTM like a 
> candidate for an independent change, and then again I fail to see why the 
> handler has to be written in the assembly language rather than C.

Again for U-Boot debug exception dumping is optional and I know many devices
not shipping with that enabled. Even if it's enabled, it will stop to work
after U-Boot's memory/global pointer being clobbered or ebase being overridden
by kernel. Not to mention that Bootloader's exception dumping won't work
with CPS secondary cores.

Paul wrote cps-vec.S and cps-vec-ns16550.S in pure assembly for reasons.
Stack pointer is not initialized at second core & we really want to reduce
code footprint on secondary core to minimize side effects before coherence
is enabled.

When the infra is here, expand it to generic early exception is just tens
of lines. I fail to see the reason to bring in hundreds lines of C code for
the same functionality.

>
>   Maciej

Although it's a pure technical discussion, I still want to expand that while
I appreciate what you have done to the MIPS, sometimes I feel like we are not
on the same page because you guys are away from frontliner for so long and
missed many contexts. MIPS is still evolving, although I never appeared here
with my corp email, I'm one of those behind the scene. I draft new architecture
specs, write AVP and internal simulators, do RTL coding for future core products,
helping customers design SoC products, design software architecture and bringing
them up. I kept FOSS as my hobby and I tried my best to keep upstream in sync with
modern practices.

I love MIPS heritages, I own an SGI Indy and Algorithmics P-4032, I made some
fixes on MAME emulator for indy to keep kernel running on it. I'm still frequently
fascinated by those brilliant old designs. But I think we still need to make progress.
While maintaining compatibility with all those old things, we need to adopt common
practices that have been proven by other architectures and make our own innovations.
We need to make the development process agile, so no developer is turned away. We
need to adopt modern booting protocols like EFI and ensure generic kernel is really
generic and not being diverted because of different loading address....

I don't know if you would agree with my in both technical details and ideology,
but I think it's the time to make my intention clear.

Thanks
-- 
- Jiaxun