[U-Boot] [PATCH 2/3] arm: relocation: clear .bss section with arch memset if defined

[Tom Rini]

On Sun, Feb 01, 2015 at 03:38:42AM +0100, Albert ARIBAUD wrote:
> Hello Przemyslaw,
> 
> On Wed, 28 Jan 2015 13:55:42 +0100, Przemyslaw Marczak
> <p.marczak at samsung.com> wrote:
> > For ARM architecture, enable the CONFIG_USE_ARCH_MEMSET/MEMCPY,
> > will highly increase the memset/memcpy performance. This is able
> > thanks to the ARM multiple register instructions.
> > 
> > Unfortunatelly the relocation is done without the cache enabled,
> > so it takes some time, but zeroing the BSS memory takes much more
> > longer, especially for the configs with big static buffers.
> > 
> > A quick test confirms, that the boot time improvement after using
> > the arch memcpy for relocation has no significant meaning.
> > The same test confirms that enable the memset for zeroing BSS,
> > reduces the boot time.
> > 
> > So this patch enables the arch memset for zeroing the BSS after
> > the relocation process. For ARM boards, this can be enabled
> > in board configs by defining: 'CONFIG_USE_ARCH_MEMSET'.
> 
> Since the issue is that zeroing is done one word at a time, could we
> not simply clear r3 as well as r2 (possibly even r4 and r5 too) and do
> a double (possibly quadruple) write loop? That would avoid calling a
> libc routine from the almost sole file in U-Boot where a C environment
> is not necessarily granted.

So this brings up something I've wondered about for a long while.  We
have arch/arm/lib/mem{set,cpy}.S which are old copies from the linux
kernel.  The kernel uses them for all ARM platforms.  Why do we not
always use these functions?  I have a very vague notion it was a size
thing...

-- 
Tom
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