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Commit 5b7eb2e9 authored by Paul Jackson's avatar Paul Jackson Committed by Thomas Gleixner
Browse files

x86 boot: longer comment explaining sanitize_e820_map routine 



Elaborate on the comment for sanitize_e820_map(), epxlaining more what
it does, what it inputs, and what it returns.  Rearrange the placement of
this comment to fit kernel conventions, before the routine's code rather
than buried inside it.

Signed-off-by: default avatarPaul Jackson <pj@sgi.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 6e9bcc79

arch/x86/kernel/e820.c

+56 −38
Original line number Diff line number Diff line
@@ -139,9 +139,64 @@ void __init e820_print_map(char *who) 
 * Sanitize the BIOS e820 map.

 *

 * Some e820 responses include overlapping entries. The following

 * replaces the original e820 map with a new one, removing overlaps.

 * replaces the original e820 map with a new one, removing overlaps,

 * and resolving conflicting memory types in favor of highest

 * numbered type.

 *

 * The input parameter biosmap points to an array of 'struct

 * e820entry' which on entry has elements in the range [0, *pnr_map)

 * valid, and which has space for up to max_nr_map entries.

 * On return, the resulting sanitized e820 map entries will be in

 * overwritten in the same location, starting at biosmap.

 *

 * The integer pointed to by pnr_map must be valid on entry (the

 * current number of valid entries located at biosmap) and will

 * be updated on return, with the new number of valid entries

 * (something no more than max_nr_map.)

 *

 * The return value from sanitize_e820_map() is zero if it

 * successfully 'sanitized' the map entries passed in, and is -1

 * if it did nothing, which can happen if either of (1) it was

 * only passed one map entry, or (2) any of the input map entries

 * were invalid (start + size < start, meaning that the size was

 * so big the described memory range wrapped around through zero.)

 *

 *	Visually we're performing the following

 *	(1,2,3,4 = memory types)...

 *

 *	Sample memory map (w/overlaps):

 *	   ____22__________________

 *	   ______________________4_

 *	   ____1111________________

 *	   _44_____________________

 *	   11111111________________

 *	   ____________________33__

 *	   ___________44___________

 *	   __________33333_________

 *	   ______________22________

 *	   ___________________2222_

 *	   _________111111111______

 *	   _____________________11_

 *	   _________________4______

 *

 *	Sanitized equivalent (no overlap):

 *	   1_______________________

 *	   _44_____________________

 *	   ___1____________________

 *	   ____22__________________

 *	   ______11________________

 *	   _________1______________

 *	   __________3_____________

 *	   ___________44___________

 *	   _____________33_________

 *	   _______________2________

 *	   ________________1_______

 *	   _________________4______

 *	   ___________________2____

 *	   ____________________33__

 *	   ______________________4_

 */



int __init sanitize_e820_map(struct e820entry *biosmap, int max_nr_map,

				int *pnr_map)

{
@@ -162,43 +217,6 @@ static struct e820entry new_bios[E820_X_MAX] __initdata; 
	int old_nr, new_nr, chg_nr;

	int i;



	/*

		Visually we're performing the following

		(1,2,3,4 = memory types)...



		Sample memory map (w/overlaps):

		   ____22__________________

		   ______________________4_

		   ____1111________________

		   _44_____________________

		   11111111________________

		   ____________________33__

		   ___________44___________

		   __________33333_________

		   ______________22________

		   ___________________2222_

		   _________111111111______

		   _____________________11_

		   _________________4______



		Sanitized equivalent (no overlap):

		   1_______________________

		   _44_____________________

		   ___1____________________

		   ____22__________________

		   ______11________________

		   _________1______________

		   __________3_____________

		   ___________44___________

		   _____________33_________

		   _______________2________

		   ________________1_______

		   _________________4______

		   ___________________2____

		   ____________________33__

		   ______________________4_

	*/



	/* if there's only one memory region, don't bother */

	if (*pnr_map < 2)

		return -1;