> -----Original Message-----
> From: David Brownell [mailto:[email protected]]
> Sent: Wednesday, March 25, 2009 4:26 PM
> To: Narnakaje, Snehaprabha
> Cc: [email protected]
> Subject: Re: [PATCH 1/3] MTD-NAND: Add support NAND devices up to 4K page
> size and 128bytes OOB
>
> On Wednesday 25 March 2009, Narnakaje, Snehaprabha wrote:
> > Unfortunately .eccpos is being used in the latest kernels
> > (as against 2.6.10/2.6.18) to calculate .oobavail in the
> > nand_base.c
>
> In 2.6.29 I see:
>
> /*
> * The number of bytes available for a client to place data into
> * the out of band area
> */
> chip->ecc.layout->oobavail = 0;
> for (i = 0; chip->ecc.layout->oobfree[i].length; i++)
> chip->ecc.layout->oobavail +=
> chip->ecc.layout->oobfree[i].length;
> mtd->oobavail = chip->ecc.layout->oobavail;
>
> So I don't quite follow ...
You are right, .eccpos it not a problem here. The .eccpos is used in the
default hwecc and swecc read_page/write_page/subpage APIs. For davinci-nand, we
override these APIs. For davinci, I can test without the change to eccpos[] and
see if it works (should). But it may be a problem in general for 4K page size
support, if there are other boards requiring to use hwecc and swecc APIs.
I guess, I also wanted to bring up another related problem with the patch I
submitted. I happen to change MTD_MAX_OOBFREE_ENTRIES to 16 from 8 and that is
used by oobfree in that structure. Wouldn't that also create a problem for the
IOCTL and existing binaries?
The above code for calculating oobavail uses the oobfree[].length and in our
case we exactly have 8 for a 4K page. But the way above code tries to come out
of the for loop is based on the length being zero ('i' could go beyond the
array limit). May be we can change this for loop and avoid change to the macro
below.
-#define MTD_MAX_OOBFREE_ENTRIES 8
+#define MTD_MAX_OOBFREE_ENTRIES 16
/*
* ECC layout control structure. Exported to userspace for
* diagnosis and to allow creation of raw images
*/
struct nand_ecclayout {
uint32_t eccbytes;
- uint32_t eccpos[64];
+ uint32_t eccpos[128];
uint32_t oobavail;
struct nand_oobfree oobfree[MTD_MAX_OOBFREE_ENTRIES];
};
Thanks
Sneha
>
>
> > If we can come up with another method to calculate .oobavail,
> > we could just leave the nand_ecclayout as is (similar to what
> > happened with nand_oobinfo)
>
>
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