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Date: Wed, 7 May 2008 10:03:25 -0500 (CDT)
From: Mark Tinguely <tinguely@casselton.net>
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To: ray@dlink.ua, tinguely@casselton.net
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Cc: freebsd-arm@freebsd.org
Subject: ARM_USE_SMALL_ALLOC question
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Alexandr Rybalko's PXA255 boot problems has tiggered a wonder that I have
had about the ARM_USE_SMALL_ALLOC option for Xscale processor.

I guess I am not a big fan of the ARM_USE_SMALL_ALLOC, so filter this
email with that bias.

				-----
the Xscale machdep initialization routines set the dump_avail array to
look like:

	dump_avail[0] = SDRAM_START;
	dump_avail[1] = SDRAM_START + memsize;

in arm/vm_machdep.c the arm_init_smallalloc() and arm_ptovirt() calculate
sizes of the memory as:

	(dump_avail[i + 1] & S_FRAME) + S_SIZE - (dump_avail[i] & S_FRAME);

It seems to me, that in most cases, SDRAM_START will be S_FRAME (1M boundary)
aligned and memsize will be a multiple of S_SIZE (1M), so my conclusion is
that these calculations in the general case will be 1MB too big.

				-----
Of course there is the ARM_HAVE_SUPERSECTIONS case, but I bet the same
general case would apply that SDRAM_START will be on a 16M boundary aligned
and memsize will be a multiple of 16M also.

This is an observation, I do not think this has caused any problems.

--Mark Tinguely.