Re: [Yaffs] bad block management

> Hi Charles,
> I am clear,
> Currently there is no YAFFS_ECC_RESULT_REFRESH, so we need to add this 
> case and the threshold as you recommend should be (refresh_threshold + ecc_strength + 1) /2, I will plan to create a patch for this.
> Do you have any proposal?
>
> Br
> White Ding
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>
> -----Original Message-----
> From: Charles Manning [mailto:cdhmanning@gmail.com]
> Sent: Thursday, August 07, 2014 5:44 AM
> To: bpqw
> Cc: yaffs@lists.aleph1.co.uk
> Subject: Re: [Yaffs] bad block management
>
> On Wed, Aug 6, 2014 at 7:26 PM, bpqw <bpqw@micron.com> wrote:
>> Hi Clarles,
>> We recommended if the bitflip over threshold we just need to refresh the block but not retire it.
>> So we doubt is it reasonable just according to the bitflips over
>> mtd->bitflip_threshold over three times to judge the block as bad block?
>>
>
> Hello White Ding
>
> I certainly understand where you are coming from here.
>
> The concern this raises is that we then lose the safety net of retiring blocks before they go bad.
>
> What we really need is two thresholds in mtd: refresh only, refresh and apply retiring logic.
>
> I suppose we could use bitflip_threshold and bitflip_strength for those, or maybe something slightly different to give more margin.
> Unfortunately the threshold and strength are often set to be the same.
>
> So I would like to use something that can be made up called, say, retire_limit.
> Where
> retire_limit = (refresh_threshold + ecc_strength + 1) /2.
>
>
> For that to work Yaffs needs another level of ECC error.
>
> How about this:
> enum yaffs_ecc_result {
>     YAFFS_ECC_RESULT_UNKNOWN,
>     YAFFS_ECC_RESULT_NO_ERROR,
>     YAFFS_ECC_RESULT_REFRESH,
>     YAFFS_ECC_RESULT_FIXED,
>     YAFFS_ECC_RESULT_UNFIXED
> };
>
> Then we can have something like, say:
>
> if errors < bitflip_threshold --> NO_ERROR else if errors < 
> retire_limit --> REFRESH else if not corrupted --> FIXED else --> 
> UNFIXED
>
> So for a concrete example, let us say we have something where:
> ecc_strength = 8, bitflip_threshold = 4 then we would have 
> retire_limit = 6
>
> So we would get the following behaviour:
>
> * 0 to 3 errors --> NO_ERROR
> * 4 to 5 errors --> REFRESH (refresh only)
> * 6 to 8 errors -->FIXED (refresh and increment chunk_error_strikes)
> * more than that --> UNFIXED.
>
> Does that make sense?
>
> Charles