microblaze: Remove noMMU code

This configuration is obsolete and likely none is really using it. That's
why remove it to simplify code.

Note about CONFIG_MMU in hw_exception_handler.S is left intentionally
for better comment understanding.

Cc: Mike Rapoport <rppt@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/43486cab370e0c0a79860120b71e0caac75a7e44.1606397528.git.michal.simek@xilinx.com

microblaze: Convert headers to SPDX license

Covert all headers to SPDX.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Stefan Asserhall <stefan.asserhall@xilinx.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>

microblaze: Fix sparse warning - fault.c

Warning log:
CHECK arch/microblaze/mm/fault.c
arch/microblaze/mm/fault.c:51:6: warning: incorrect type in initializer (different address spaces)
arch/microblaze/mm/fault.c:51:6: expected unknown type 2const [noderef] *__gu_addr<asn:1>
arch/microblaze/mm/fault.c:51:6: got unsigned int *<noident>
arch/microblaze/mm/fault.c:68:6: warning: symbol 'bad_page_fault' was not declared. Should it be static?

Signed-off-by: Michal Simek <monstr@monstr.eu>

microblaze: Fix sparse warning - sw_exceptions

Function sw_exception is linked with asm code.

Warning log:
CHECK arch/microblaze/kernel/exceptions.c
arch/microblaze/kernel/exceptions.c:53:6: warning: symbol 'sw_exception' was not declared. Should it be static?

Signed-off-by: Michal Simek <monstr@monstr.eu>

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>

microblaze: Add stack unwinder

Implement intelligent backtracing by searching for stack frame creation,
and emitting only return addresses. Use print_hex_dump() to display the
entire binary kernel stack.

Limitation: MMU kernels are not currently able to trace beyond a system trap
(interrupt, syscall, etc.). It is the intent of this patch to provide
infrastructure that can be extended to add this capability later.

Changes from V1:
* Removed checks in find_frame_creation() that prevented location of the frame
creation instruction in heavily optimized code
* Various formatting/commenting/file location tweaks per review comments
* Dropped Kconfig option to enable STACKTRACE as something logically separate

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>

microblaze: Remove ancient code

I found several function which we don't use that's why I am removing them.

Signed-off-by: Michal Simek <monstr@monstr.eu>

microblaze_mmu_v2: Traps MMU update

Signed-off-by: Michal Simek <monstr@monstr.eu>

microblaze: Add missing declaration for die and _exception func

This change remove sparse errors.

Signed-off-by: Michal Simek <monstr@monstr.eu>

microblaze_v8: exception handling

Reviewed-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>
Acked-by: John Linn <john.linn@xilinx.com>
Acked-by: John Williams <john.williams@petalogix.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>