Re: [RESEND PATCH v2 0/3] mtd: use ONFI bad blocks per LUN to calculate UBI bad PEB limit

From: Boris Brezillon
Date: Thu Oct 27 2016 - 15:57:03 EST


Hi Zach,

Please do not resend after only one week. Reviewing this series was on
my TODO list ;).

On Thu, 27 Oct 2016 14:13:59 -0500
Zach Brown <zach.brown@xxxxxx> wrote:

> For ONFI-compliant NAND devices, the ONFI parameters report the maximum number
> of bad blocks per LUN that will be encountered over the lifetime of the device,
> so we can use that information to get a more accurate (and smaller) value for
> the UBI bad PEB limit.
>
> The ONFI parameter "maxiumum number of bad blocks per LUN" is the max number of
> bad blocks that each individual LUN will ever ecounter. It is not the number of
> bad blocks to reserve for the nand device per LUN in the device.
>
> This means that in the worst case a UBI device spanning X LUNs will encounter
> "maximum number of bad blocks per LUN" * X bad blocks. The implementation in
> this patch assumes this worst case and allocates bad block accordingly.

That's a discussion I had with Richard a few months ago, and I didn't
know someone had already proposed a patch for that. So that's all good
news.
Indeed, I really think we should use information retrieved at flash
detection time rather than asking the user to explicitly tweak the
bad_peb_limit value for its chip.

>
> These patches are ordered in terms of their dependencies, but ideally, all 3
> would need to be applied for this to work as intended.
>
> v1:
> * Changed commit message to address concerns from v1[1] about this patch set
> making best case assumptions.
>
> [1]
> http://lkml.iu.edu/hypermail/linux/kernel/1505.1/04822.html
>
> Jeff Westfahl (3):
> mtd: introduce function max_bad_blocks
> mtd: nand: implement 'max_bad_blocks' mtd function
> mtd: ubi: use 'max_bad_blocks' to compute bad_peb_limit if available
>
> drivers/mtd/mtdpart.c | 12 ++++++++++++
> drivers/mtd/nand/nand_base.c | 34 ++++++++++++++++++++++++++++++++++
> drivers/mtd/ubi/build.c | 9 +++++++++
> include/linux/mtd/mtd.h | 1 +
> 4 files changed, 56 insertions(+)
>