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Date: Fri, 07 Jun 2013 21:03:26 +1200
From: Tony Prisk <linux@prisktech.co.nz>
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To: linux--arm-kernel@lists.infradead.org
Subject: NAND buffer allocation fails
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Could someone explain why the following situation might occur:

In drivers/mtd/nand/nand_base.c, we have:

int nand_scan_tail(struct mtd_info *mtd)
{
     int i;
     struct nand_chip *chip = mtd->priv;

     /* New bad blocks should be marked in OOB, flash-based BBT, or both */
     BUG_ON((chip->bbt_options & NAND_BBT_NO_OOB_BBM) &&
             !(chip->bbt_options & NAND_BBT_USE_FLASH));

     if (!(chip->options & NAND_OWN_BUFFERS))
         chip->buffers = kmalloc(sizeof(*chip->buffers), GFP_KERNEL);
     if (!chip->buffers)
         return -ENOMEM;
...

For some reason, the kmalloc always fails on my configuration/hardware 
(arch-vt8500: WonderMedia/VIA APC8750).

The strange thing is that if I add the NAND_OWN_BUFFERS option, and 
allocate my own buffers in the driver probe everything is fine.
Driver probe code below:

     priv->nand.buffers = devm_kzalloc(priv->dev, 
sizeof(*priv->nand.buffers), GFP_KERNEL);
     if (!priv->nand.buffers) {
         dev_err(priv->dev, "failed to allocate NAND buffers\n");
         return -ENOMEM;
     }

The devm_kzalloc does occur earlier than the nand_scan_tail alloc would 
have, but there doesn't appear to be a shortage of memory on the 
platform so I don't think it's failing for a memory shortage.

Is there any real difference between using kmalloc and devm_kzalloc to 
allocate the buffer (other than the obvious 0'ing of the buffer)?
Why would one call fail and the other succeed?

Regards
Tony Prisk