microblaze: Add KGDB support

Kgdb uses brki r16, 0x18 instruction to call
low level _debug_exception function which save
current state to pt_regs and call microblaze_kgdb_break
function. _debug_exception should be called only from
the kernel space. User space calling is not supported
because user application debugging uses different handling.

pt_regs_to_gdb_regs loads additional special registers
which can't be changed

 * Enable KGDB in Kconfig
 * Remove ancient not-tested KGDB support
 * Remove ancient _debug_exception code from entry.S

Only MMU KGDB support is supported.

Signed-off-by: Michal Simek <monstr@monstr.eu>
CC: Jason Wessel <jason.wessel@windriver.com>
CC: John Williams <john.williams@petalogix.com>
CC: Edgar E. Iglesias <edgar.iglesias@petalogix.com>
CC: linux-kernel@vger.kernel.org
Acked-by: Jason Wessel <jason.wessel@windriver.com>

8 files changed, 234 insertions, 81 deletions

diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index a51742190c12..be3855250db6 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -14,6 +14,7 @@ config MICROBLAZE
         select USB_ARCH_HAS_EHCI
         select ARCH_WANT_OPTIONAL_GPIOLIB
         select HAVE_OPROFILE
+        select HAVE_ARCH_KGDB
         select HAVE_DMA_ATTRS
         select HAVE_DMA_API_DEBUG
         select TRACING_SUPPORT
diff --git a/arch/microblaze/include/asm/exceptions.h b/arch/microblaze/include/asm/exceptions.h
index fa0e36657fdd..6479097b802b 100644
--- a/arch/microblaze/include/asm/exceptions.h
+++ b/arch/microblaze/include/asm/exceptions.h
@@ -69,22 +69,6 @@ asmlinkage void full_exception(struct pt_regs *regs, unsigned int type,
 void die(const char *str, struct pt_regs *fp, long err);
 void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr);
 
-#if defined(CONFIG_KGDB)
-void (*debugger)(struct pt_regs *regs);
-int (*debugger_bpt)(struct pt_regs *regs);
-int (*debugger_sstep)(struct pt_regs *regs);
-int (*debugger_iabr_match)(struct pt_regs *regs);
-int (*debugger_dabr_match)(struct pt_regs *regs);
-void (*debugger_fault_handler)(struct pt_regs *regs);
-#else
-#define debugger(regs)                  do { } while (0)
-#define debugger_bpt(regs)              0
-#define debugger_sstep(regs)            0
-#define debugger_iabr_match(regs)       0
-#define debugger_dabr_match(regs)       0
-#define debugger_fault_handler          ((void (*)(struct pt_regs *))0)
-#endif
-
 #endif /*__ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ASM_MICROBLAZE_EXCEPTIONS_H */
diff --git a/arch/microblaze/include/asm/kgdb.h b/arch/microblaze/include/asm/kgdb.h
new file mode 100644
index 000000000000..78b17d40b235
--- /dev/null
+++ b/arch/microblaze/include/asm/kgdb.h
@@ -0,0 +1,28 @@
+#ifdef __KERNEL__
+#ifndef __MICROBLAZE_KGDB_H__
+#define __MICROBLAZE_KGDB_H__
+
+#ifndef __ASSEMBLY__
+
+#define CACHE_FLUSH_IS_SAFE     1
+#define BUFMAX                  2048
+
+/*
+ * 32 32-bit general purpose registers (r0-r31)
+ *  6 32-bit special registers (pc, msr, ear, esr, fsr, btr)
+ * 12 32-bit PVR
+ *   7 32-bit MMU Regs (redr, rpid, rzpr, rtlbx, rtlbsx, rtlblo, rtlbhi)
+ * ------
+ *  57 registers
+ */
+#define NUMREGBYTES     (57 * 4)
+
+#define BREAK_INSTR_SIZE        4
+static inline void arch_kgdb_breakpoint(void)
+{
+        __asm__ __volatile__("brki r16, 0x18;");
+}
+
+#endif /* __ASSEMBLY__ */
+#endif /* __MICROBLAZE_KGDB_H__ */
+#endif /* __KERNEL__ */
diff --git a/arch/microblaze/kernel/Makefile b/arch/microblaze/kernel/Makefile
index d66ddef53c07..5eecc9f1fbd9 100644
--- a/arch/microblaze/kernel/Makefile
+++ b/arch/microblaze/kernel/Makefile
@@ -28,5 +28,6 @@ obj-$(CONFIG_MODULES)		+= microblaze_ksyms.o module.o
 obj-$(CONFIG_MMU)               += misc.o
 obj-$(CONFIG_STACKTRACE)        += stacktrace.o
 obj-$(CONFIG_FUNCTION_TRACER)   += ftrace.o mcount.o
+obj-$(CONFIG_KGDB)              += kgdb.o
 
 obj-y   += entry$(MMU).o
diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
index 5a5cb5842938..304882e56459 100644
--- a/arch/microblaze/kernel/entry.S
+++ b/arch/microblaze/kernel/entry.S
@@ -745,11 +745,8 @@ IRQ_return: /* MS: Make global symbol for debugging */
         nop
 
 /*
- * `Debug' trap
- *  We enter dbtrap in "BIP" (breakpoint) mode.
- *  So we exit the breakpoint mode with an 'rtbd' and proceed with the
- *  original dbtrap.
- *  however, wait to save state first
+ * Debug trap for KGDB. Enter to _debug_exception by brki r16, 0x18
+ * and call handling function with saved pt_regs
  */
 C_ENTRY(_debug_exception):
         /* BIP bit is set on entry, no interrupts can occur */
@@ -759,18 +756,44 @@ C_ENTRY(_debug_exception):
         nop
         andi    r1, r1, MSR_UMS
         bnei    r1, 1f
-        /* Kernel-mode state save.  */
+/* MS: Kernel-mode state save - kgdb */
         lwi     r1, r0, TOPHYS(PER_CPU(ENTRY_SP)); /* Reload kernel stack-ptr*/
-        tophys(r1,r1);
 
-        addik   r1, r1, -STATE_SAVE_SIZE; /* Make room on the stack.  */
+        /* BIP bit is set on entry, no interrupts can occur */
+        addik   r1, r1, CONFIG_KERNEL_BASE_ADDR - CONFIG_KERNEL_START - STATE_SAVE_SIZE;
         SAVE_REGS;
+        /* save all regs to pt_reg structure */
+        swi     r0, r1, PTO+PT_R0;      /* R0 must be saved too */
+        swi     r14, r1, PTO+PT_R14     /* rewrite saved R14 value */
+        swi     r16, r1, PTO+PT_R16
+        swi     r16, r1, PTO+PT_PC; /* PC and r16 are the same */
+        swi     r17, r1, PTO+PT_R17
+        /* save special purpose registers to pt_regs */
+        mfs     r11, rear;
+        swi     r11, r1, PTO+PT_EAR;
+        mfs     r11, resr;
+        swi     r11, r1, PTO+PT_ESR;
+        mfs     r11, rfsr;
+        swi     r11, r1, PTO+PT_FSR;
+
+        /* stack pointer is in physical address at it is decrease
+         * by STATE_SAVE_SIZE but we need to get correct R1 value */
+        addik   r11, r1, CONFIG_KERNEL_START - CONFIG_KERNEL_BASE_ADDR + STATE_SAVE_SIZE;
+        swi     r11, r1, PTO+PT_R1
+        /* MS: r31 - current pointer isn't changed */
+        tovirt(r1,r1)
+#ifdef CONFIG_KGDB
+        addi    r5, r1, PTO /* pass pt_reg address as the first arg */
+        la      r15, r0, dbtrap_call; /* return address */
+        rtbd    r0, microblaze_kgdb_break
+        nop;
+#endif
+        /* MS: Place handler for brki from kernel space if KGDB is OFF.
+         * It is very unlikely that another brki instruction is called. */
+        bri 0
 
-        swi     r1, r1, PTO + PT_MODE;
-        brid    2f;
-        nop;                            /* Fill delay slot */
-1:      /* User-mode state save.  */
-        lwi     r1, r0, TOPHYS(PER_CPU(CURRENT_SAVE)); /* get saved current */
+/* MS: User-mode state save - gdb */
+1:      lwi     r1, r0, TOPHYS(PER_CPU(CURRENT_SAVE)); /* get saved current */
         tophys(r1,r1);
         lwi     r1, r1, TS_THREAD_INFO; /* get the thread info */
         addik   r1, r1, THREAD_SIZE;    /* calculate kernel stack pointer */
@@ -781,36 +804,32 @@ C_ENTRY(_debug_exception):
         swi     r17, r1, PTO+PT_R17;
         swi     r16, r1, PTO+PT_R16;
         swi     r16, r1, PTO+PT_PC;     /* Save LP */
-
         swi     r0, r1, PTO + PT_MODE; /* Was in user-mode.  */
         lwi     r11, r0, TOPHYS(PER_CPU(ENTRY_SP));
         swi     r11, r1, PTO+PT_R1; /* Store user SP.  */
-2:      lwi     CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
+        lwi     CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
         tovirt(r1,r1)
-
         set_vms;
         addik   r5, r1, PTO;
         addik   r15, r0, dbtrap_call;