[U-Boot] [PATCH v4 0/6] Enable Thumb build for ARM platforms

Aneesh V aneesh at ti.com
Thu Mar 8 18:20:16 CET 2012

Thumb is an alternate instruction set available in many
ARM processors. Below is a detailed description from ARM

"The Thumb instruction set is a re-encoded subset of the
ARM instruction set. Thumb instructions execute in their
own processor state, with the architecture defining the
mechanisms required to transition between ARM and Thumb
states. The key difference is that Thumb instructions are
half the size of ARM instructions(16 bits compared with 32
bits). Greater code density can usually be achieved by using
the Thumb instruction set in preference to the ARM instruction
set, at a cost of some reduction in performance"

"In ARMv6T2, Thumb-2 technology is introduced. This technology
makes it possible to extend the original Thumb instruction set
with many 32-bit instructions. The range of 32-bit Thumb instructions
included in ARMv6T2 permits Thumb code to achieve performance
similar to ARM code, with code density better than that of earlier
Thumb code. From ARMv6T2, the ARM and Thumb instruction sets provide
almost identical functionality"

This series adds Thumb support in U-Boot and enables it for
OMAP4. It also fixes issues faced while booting OMAP4 with
Thumb-2 images of U-Boot and SPL.

Thumb mode is becoming increasingly relevant for U-Boot with
the advent of SPL. It's very important to keep SPL size smaller
considering the internal RAM size constraints on many platforms.
On OMAP4 the size reduction enables us to use SPL on secure devices
that have smaller internal RAM available for non-secure world. 

To enable support for new platforms you just need to add
CONFIG_SYS_THUMB_BUILD in your config file.

Tool-chains tried:
1. Sourcery G++ Lite 2010q1-202
arm-none-linux-gnueabi-gcc (Sourcery G++ Lite 2010q1-202) 4.4.1
GNU ld (Sourcery G++ Lite 2010q1-202) - binutils

2. Linaro 4.6-2012.01
arm-linux-gnueabi-gcc (crosstool-NG linaro-1.13.1-2012.01-20120125 -
	Linaro GCC 2012.01) 4.6.3 20120105 (prerelease)
GNU ld (crosstool-NG linaro-1.13.1-2012.01-20120125 - Linaro GCC 2012.01) 2.22

Code-size reduction:
Image		ARM build	Thumb build	% Reduction
u-boot.bin	190408		144676		24.01%
u-boot-spl.bin	33200		25096		24.40%

Performance(timestamp just before the main loop):
ARM build	Thumb build	% Reduction
898510us	878247us	-2.25%

Performance actually improved marginally for the Thumb
build, maybe because of the reduced image sizes. 

Aneesh V (6):
  arm: adapt asm/linkage.h from Linux
  armv7: add appropriate headers for assembly functions
  ARM: enable Thumb build
  armv7: Use -march=armv7-a and thereby enable Thumb-2
  omap4+: Avoid using __attribute__ ((__packed__))
  OMAP4: enable Thumb build

 README                                         |    8 +++++
 arch/arm/config.mk                             |   22 +++++++++----
 arch/arm/cpu/armv7/config.mk                   |    7 +++-
 arch/arm/cpu/armv7/mx5/lowlevel_init.S         |    5 ++-
 arch/arm/cpu/armv7/mx6/lowlevel_init.S         |    5 ++-
 arch/arm/cpu/armv7/omap-common/lowlevel_init.S |   14 ++++----
 arch/arm/cpu/armv7/omap-common/reset.S         |    5 ++-
 arch/arm/cpu/armv7/omap3/lowlevel_init.S       |   41 ++++++++++++-----------
 arch/arm/cpu/armv7/s5pc1xx/cache.S             |   10 +++--
 arch/arm/cpu/armv7/s5pc1xx/reset.S             |    5 ++-
 arch/arm/cpu/armv7/start.S                     |   13 ++++---
 arch/arm/cpu/armv7/tegra2/lowlevel_init.S      |    5 ++-
 arch/arm/cpu/armv7/u8500/lowlevel.S            |    9 +++--
 arch/arm/include/asm/arch-omap4/mux_omap4.h    |    2 +-
 arch/arm/include/asm/arch-omap5/mux_omap5.h    |    2 +-
 arch/arm/include/asm/linkage.h                 |    7 ++++
 include/configs/omap4_common.h                 |    2 +
 include/linux/linkage.h                        |    7 +++-
 18 files changed, 106 insertions(+), 63 deletions(-)
 create mode 100644 arch/arm/include/asm/linkage.h

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