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# This is a simple script that checks the contents of /proc/mtrr to see if

# the BIOS maker for the computer took the easy way out in terms of

# specifying memory regions when there is a hole below 4GB for PCI access

# and the machine has 4GB or more of RAM.  When the contents of /proc/mtrr

# show a 4GB mapping of write-back cached RAM, minus punch out hole(s) of

# uncacheable regions (the area reserved for PCI access), then it becomes

# impossible for the ib_ipath driver to set write_combining on its PIO

# buffers.  To correct the problem, remap the lower memory region in various

# chunks up to the start of the punch out hole(s), then delete the punch out

# hole(s) entirely as they aren't needed any more.  That way, ib_ipath will

# be able to set write_combining on its PIO memory access region.

BEGIN {

	regs = 0

}

function check_base(mem)

{

	printf "Base memory data: base=0x%08x, size=0x%x\n", base[mem], size[mem] > "/dev/stderr"

	if (size[mem] < (512 * 1024 * 1024))

		return 0

	if (type[mem] != "write-back")

		return 0

	if (base[mem] >= (4 * 1024 * 1024 * 1024))

		return 0

	return 1

}

function check_hole(hole)

{

	printf "Hole data: base=0x%08x, size=0x%x\n", base[hole], size[hole] > "/dev/stderr"

	if (size[hole] > (1 * 1024 * 1024 * 1024))

		return 0

	if (type[hole] != "uncachable")

		return 0

	if ((base[hole] + size[hole]) > (4 * 1024 * 1024 * 1024))

		return 0

	return 1

}

function build_entries(start, end,     new_base, new_size, tmp_base)

{

	# mtrr registers require alignment of blocks, so a 256MB chunk must

	# be 256MB aligned.  Additionally, all blocks must be a power of 2

	# in size.  So, do the largest power of two size that we can and

	# still have start + block <= end, rinse and repeat.

	tmp_base = start

	do {

		new_base = tmp_base

		new_size = 4096

		while (((new_base + new_size) < end) &&

		       ((new_base % new_size) == 0))

			new_size = lshift(new_size, 1)

		if (((new_base + new_size) > end) ||

		    ((new_base % new_size) != 0))

			new_size = rshift(new_size, 1)

		printf "base=0x%x size=0x%x type=%s\n",

			new_base, new_size, type[mem] > "/dev/stderr"

		printf "base=0x%x size=0x%x type=%s\n",

			new_base, new_size, type[mem] > "/proc/mtrr"

		fflush("")

		tmp_base = new_base + new_size

	} while (tmp_base < end)

}

{

	gsub("^reg", "")

	gsub(": base=", " ")

	gsub(" [(].*), size=", " ")

	gsub(": ", " ")

	gsub(", count=.*$", "")

	register[regs] = strtonum($1)

	base[regs] = strtonum($2)

	size[regs] = strtonum($3)

	human_size[regs] = size[regs]

	if (match($3, "MB")) { size[regs] *= 1024*1024; mult[regs] = "MB" }

	else { size[regs] *= 1024; mult[regs] = "KB" }

	type[regs] = $4

	enabled[regs] = 1

	end[regs] = base[regs] + size[regs]

	regs++

}

END {

	# First we need to find our base memory region.  We only care about

	# the memory register that starts at base 0.  This is the only one

	# that we can reliably know is our global memory region, and the

	# only one that we can reliably check against overlaps.  It's entirely

	# possible that any memory region not starting at 0 and having an

	# overlap with another memory region is in fact intentional and we

	# shouldn't touch it.

	for(i=0; i<regs; i++)

		if (base[i] == 0)

			break

	# Did we get a valid base register?

	if (i == regs)

		exit 1

	mem = i

	if (!check_base(mem))

		exit 1

	cur_hole = 0

	for(i=0; i<regs; i++) {

		if (i == mem)

			continue

		if (base[i] < end[mem] && check_hole(i))

			holes[cur_hole++] = i

	}

	if (cur_hole == 0) {

		print "Nothing to do" > "/dev/stderr"

		exit 1

	}

	printf "Found %d punch-out holes\n", cur_hole > "/dev/stderr"

	# We need to sort the holes according to base address

	for(j = 0; j < cur_hole - 1; j++) {

		for(i = cur_hole - 1; i > j; i--) {

			if(base[holes[i]] < base[holes[i-1]]) {

				tmp = holes[i]

				holes[i] = holes[i-1]

				holes[i-1] = tmp

			}

		}

	}

	# OK, the common case would be that the BIOS is mapping holes out

	# of the 4GB memory range, and that our hole(s) are consecutive and

	# that our holes and our memory region end at the same place.  However,

	# things like machines with 8GB of RAM or more can foul up these

	# common traits.

	#

	# So, our modus operandi is to disable all of the memory/hole regions

	# to start, then build new base memory zones that in the end add

	# up to the same as our original zone minus the holes.  We know that

	# we will never have a hole listed here that belongs to a valid

	# hole punched in a write-combining memory region because you can't

	# overlay write-combining on top of write-back and we know our base

	# memory region is write-back, so in order for this hole to overlap

	# our base memory region it can't be also overlapping a write-combining

	# region.

	printf "disable=%d\n", register[mem] > "/dev/stderr"

	printf "disable=%d\n", register[mem] > "/proc/mtrr"

	fflush("")

	enabled[mem] = 0

	for(i=0; i < cur_hole; i++) {

		printf "disable=%d\n", register[holes[i]] > "/dev/stderr"

		printf "disable=%d\n", register[holes[i]] > "/proc/mtrr"

		fflush("")

		enabled[holes[i]] = 0

	}

	build_entries(base[mem], base[holes[0]])

	for(i=0; i < cur_hole - 1; i++)

		if (base[holes[i+1]] > end[holes[i]])

			build_entries(end[holes[i]], base[holes[i+1]])

	if (end[mem] > end[holes[i]])

		build_entries(end[holes[i]], end[mem])

	# We changed up the mtrr regs, so signal to the rdma script to

	# reload modules that need the mtrr regs to be right.

	exit 0

}