NOMMU: Add support for direct mapping through mtdconcat if possible

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=6e232cfce35a20a8702d9ac7709d35030c1b3271
Commit:     6e232cfce35a20a8702d9ac7709d35030c1b3271
Parent:     402d326519c1a4859c527702383f4e60f606ef52
Author:     David Howells <dhowells at redhat.com>
AuthorDate: Thu Feb 12 10:40:05 2009 +0000
Committer:  David Woodhouse <David.Woodhouse at intel.com>
CommitDate: Tue Mar 24 09:01:08 2009 +0000

    NOMMU: Add support for direct mapping through mtdconcat if possible
    
    Add support for direct mapping through mtdconcat, if possible, by attaching the
    samebacking_dev_info structure to the master.
    
    It has some restrictions:
    
     (1) It won't permit direct mapping of concatenated devices that have differing
         BDIs.
    
     (2) It doesn't support maps that span the 'gap' between devices, although it
         possibly could if the devices spanned across return compatible
         (ie. contiguous) addresses from their get_unmapped_area() ops.
    
    Signed-off-by: Gavin Lambert <gavinl at compacsort.com>
    Signed-off-by: David Howells <dhowells at redhat.com>
    Tested-by: Bernd Schmidt <bernd.schmidt at analog.com>
    Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
---
 drivers/mtd/mtdconcat.c |   47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 47 insertions(+), 0 deletions(-)

diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
index 3dbb1b3..792b547 100644
--- a/drivers/mtd/mtdconcat.c
+++ b/drivers/mtd/mtdconcat.c
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/types.h>
+#include <linux/backing-dev.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/concat.h>
@@ -684,6 +685,40 @@ static int concat_block_markbad(struct mtd_info *mtd, loff_t ofs)
 }
 
 /*
+ * try to support NOMMU mmaps on concatenated devices
+ * - we don't support subdev spanning as we can't guarantee it'll work
+ */
+static unsigned long concat_get_unmapped_area(struct mtd_info *mtd,
+					      unsigned long len,
+					      unsigned long offset,
+					      unsigned long flags)
+{
+	struct mtd_concat *concat = CONCAT(mtd);
+	int i;
+
+	for (i = 0; i < concat->num_subdev; i++) {
+		struct mtd_info *subdev = concat->subdev[i];
+
+		if (offset >= subdev->size) {
+			offset -= subdev->size;
+			continue;
+		}
+
+		/* we've found the subdev over which the mapping will reside */
+		if (offset + len > subdev->size)
+			return (unsigned long) -EINVAL;
+
+		if (subdev->get_unmapped_area)
+			return subdev->get_unmapped_area(subdev, len, offset,
+							 flags);
+
+		break;
+	}
+
+	return (unsigned long) -ENOSYS;
+}
+
+/*
  * This function constructs a virtual MTD device by concatenating
  * num_devs MTD devices. A pointer to the new device object is
  * stored to *new_dev upon success. This function does _not_
@@ -740,6 +775,8 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 
 	concat->mtd.ecc_stats.badblocks = subdev[0]->ecc_stats.badblocks;
 
+	concat->mtd.backing_dev_info = subdev[0]->backing_dev_info;
+
 	concat->subdev[0] = subdev[0];
 
 	for (i = 1; i < num_devs; i++) {
@@ -766,6 +803,15 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 				concat->mtd.flags |=
 				    subdev[i]->flags & MTD_WRITEABLE;
 		}
+
+		/* only permit direct mapping if the BDIs are all the same
+		 * - copy-mapping is still permitted
+		 */
+		if (concat->mtd.backing_dev_info !=
+		    subdev[i]->backing_dev_info)
+			concat->mtd.backing_dev_info =
+				&default_backing_dev_info;
+
 		concat->mtd.size += subdev[i]->size;
 		concat->mtd.ecc_stats.badblocks +=
 			subdev[i]->ecc_stats.badblocks;
@@ -796,6 +842,7 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 	concat->mtd.unlock = concat_unlock;
 	concat->mtd.suspend = concat_suspend;
 	concat->mtd.resume = concat_resume;
+	concat->mtd.get_unmapped_area = concat_get_unmapped_area;
 
 	/*
 	 * Combine the erase block size info of the subdevices: