[MTD] [NAND] Verify probe by retrying to checking the results match

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=ed8165c75e3dd0b2e51b92a858cabe29ba00c9cb
Commit:     ed8165c75e3dd0b2e51b92a858cabe29ba00c9cb
Parent:     37e5ffa3f15bd9a8b133ab13e9bef833b5eb33d4
Author:     Ben Dooks <ben-linux at fluff.org>
AuthorDate: Mon Apr 14 14:58:58 2008 +0100
Committer:  David Woodhouse <dwmw2 at infradead.org>
CommitDate: Tue Apr 22 21:43:06 2008 +0100

    [MTD] [NAND] Verify probe by retrying to checking the results match
    
    With modern systems using bus-hold instead of bus pull-up, it can
    often lead to erroneous reporting of NAND devices where there are
    none. Do a double probe to ensure that the result we got the first
    time is repeatable, and if it is not then return that there is no
    chip there.
    
    Signed-off-by: Ben Dooks <ben-linux at fluff.org>
    Signed-off-by: David Woodhouse <dwmw2 at infradead.org>
---
 drivers/mtd/nand/nand_base.c |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 7acb1a0..ba1bdf7 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -2229,6 +2229,7 @@ static struct nand_flash_dev *nand_get_flash_type(struct mtd_info *mtd,
 {
 	struct nand_flash_dev *type = NULL;
 	int i, dev_id, maf_idx;
+	int tmp_id, tmp_manf;
 
 	/* Select the device */
 	chip->select_chip(mtd, 0);
@@ -2240,6 +2241,26 @@ static struct nand_flash_dev *nand_get_flash_type(struct mtd_info *mtd,
 	*maf_id = chip->read_byte(mtd);
 	dev_id = chip->read_byte(mtd);
 
+	/* Try again to make sure, as some systems the bus-hold or other
+	 * interface concerns can cause random data which looks like a
+	 * possibly credible NAND flash to appear. If the two results do
+	 * not match, ignore the device completely.
+	 */
+
+	chip->cmdfunc(mtd, NAND_CMD_READID, 0x00, -1);
+
+	/* Read manufacturer and device IDs */
+
+	tmp_manf = chip->read_byte(mtd);
+	tmp_id = chip->read_byte(mtd);
+
+	if (tmp_manf != *maf_id || tmp_id != dev_id) {
+		printk(KERN_INFO "%s: second ID read did not match "
+		       "%02x,%02x against %02x,%02x\n", __func__,
+		       *maf_id, dev_id, tmp_manf, tmp_id);
+		return ERR_PTR(-ENODEV);
+	}
+
 	/* Lookup the flash id */
 	for (i = 0; nand_flash_ids[i].name != NULL; i++) {
 		if (dev_id == nand_flash_ids[i].id) {