this patch i a port of following patch from u-boot with some additional
integration changes and fixes of original code:
| Subject: [PATCH] MIPS: Stop building position independent code
|
| U-Boot has up until now built with -fpic for the MIPS architecture,
| producing position independent code which uses indirection through a
| global offset table, making relocation fairly straightforward as it
| simply involves patching up GOT entries.
|
| Using -fpic does however have some downsides. The biggest of these is
| that generated code is bloated in various ways. For example, function
| calls are indirected through the GOT & the t9 register:
|
|   8f998064   lw     t9,-32668(gp)
|   0320f809   jalr   t9
|
| Without -fpic the call is simply:
|
|   0f803f01   jal    be00fc04 <puts>
|
| This is more compact & faster (due to the lack of the load & the
| dependency the jump has on its result). It is also easier to read &
| debug because the disassembly shows what function is being called,
| rather than just an offset from gp which would then have to be looked up
| in the ELF to discover the target function.
|
| Another disadvantage of -fpic is that each function begins with a
| sequence to calculate the value of the gp register, for example:
|
|   3c1c0004   lui    gp,0x4
|   279c3384   addiu  gp,gp,13188
|   0399e021   addu   gp,gp,t9
|
| Without using -fpic this sequence no longer appears at the start of each
| function, reducing code size considerably.
|
| This patch switches U-Boot from building with -fpic to building with
| -fno-pic, in order to gain the benefits described above. The cost of
| this is an extra step during the build process to extract relocation
| data from the ELF & write it into a new .rel section in a compact
| format, plus the added complexity of dealing with multiple types of
| relocation rather than the single type that applied to the GOT. The
| benefit is smaller, cleaner, more debuggable code. The relocate_code()
| function is reimplemented in C to handle the new relocation scheme,
| which also makes it easier to read & debug.
|
| Taking maltael_defconfig as an example the size of u-boot.bin built
| using the Codescape MIPS 2016.05-06 toolchain (gcc 4.9.2, binutils
| 2.24.90) shrinks from 254KiB to 224KiB.
|
| Signed-off-by: Paul Burton <paul.burton@imgtec.com>

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

At least some ath79 SoC have build in 32K RAM. It allow us to use
lowlevel portion of barebox to bootstrap the system by using JTAG
debugger (For example OpenOCD).
Since ath79 has no reliable way to stop the CPU execution before
reading SPI Flash, this can cause different issues. To avoid it, we
need to flash a execution trap with software debug breakpoint to the
flash.

The workflow should be as follow:
- After power on or reset the CPU will start execution of SPI flash.
  As soon as software debug breakpoint is executed, CPU will halt and
  notify OpenOCD about breakpoint event.
- OpenOCD will load reduced barebox to SRAM and execute it.
  This part will do all needed low level initialization - PLL, RAM and
  trigger second breakpoint event.
- OpenOCD will load full barebox version to the main RAM and start
  execution.

It can be used for bring-up, so no regular flashing is needed.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

This is a port of Linux kernel commit

| commit 740129b
| Author: Antony Pavlov <antonynpavlov@gmail.com>
| Date:   Wed Apr 11 08:50:19 2018 +0100
|
|     MIPS: Use generic GCC library routines from lib/

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

10x performance gain according to simple test on QEMU malta:
barebox:/ time memcpy 0xa0000000 0xa0001000 0x100000

Signed-off-by: Aleksey Kuleshov <rndfax@yandex.ru>
Acked-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Also ignore piggy.shipped binary (CONFIG_IMAGE_COMPRESSION_NONE=y).

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Checking exception handling:

    $ make qemu-malta_defconfig
    $ make

    ...

    $ qemu-system-mips -nodefaults -M malta -m 256 \
       -nographic -serial stdio -bios ./barebox.bin

    ...

    barebox:/ md -l 0x03

    Ooops, address error on load or ifetch!
    EPC = 0xa082783c
    CP0_STATUS = 0x00000006
    CP0_CAUSE = 0x00000410
    CP0_CONFIG = 0x80008482

    ### ERROR ### Please RESET the board ###

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Add start.S, CP0 clocksource, Makefile, linker script and memory
layout function.

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>