Messages in this thread | | | Date | Mon, 2 Jan 2023 11:06:20 -0600 | From | Samuel Holland <> | Subject | Re: [PATCH 4/7] mtd: rawnand: sunxi: Fix ECC strength maximization |
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Hi Miquèl,
On 1/2/23 10:45, Miquel Raynal wrote: >>>> This is already accounted for in the subtraction for OOB, since the BBM >>>> overlaps the first OOB dword. With this change, the driver picks the >>>> same ECC strength as the vendor driver. >>>> >>>> Fixes: 4796d8655915 ("mtd: nand: sunxi: Support ECC maximization") >>>> Signed-off-by: Samuel Holland <samuel@sholland.org> >>>> --- >>>> >>>> drivers/mtd/nand/raw/sunxi_nand.c | 3 +-- >>>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c >>>> index 1bddeb1be66f..1ecf2cee343b 100644 >>>> --- a/drivers/mtd/nand/raw/sunxi_nand.c >>>> +++ b/drivers/mtd/nand/raw/sunxi_nand.c >>>> @@ -1643,8 +1643,7 @@ static int sunxi_nand_hw_ecc_ctrl_init(struct nand_chip *nand, >>>> ecc->size = 1024; >>>> nsectors = mtd->writesize / ecc->size; >>>> >>>> - /* Reserve 2 bytes for the BBM */ >>>> - bytes = (mtd->oobsize - 2) / nsectors; >>>> + bytes = mtd->oobsize / nsectors; >>> >>> I'm sorry but I don't think we can make this work. This change would >>> break all existing users... >> >> OK, it is not too much of an issue because I can manually specify the >> ECC parameters in the devicetree. Do you think it makes sense to fix >> this when adding new hardware variants/compatible strings? > > Actually, looking at the code again, I don't get how the above diff > could be valid. The "maximize strength" logic (in which this diff is) > looks for the biggest region to store ECC bytes. These bytes cannot > be stored on the BBM, which "mtd->oobsize - 2" tries to avoid, so we > cannot get rid of this.
Right, we cannot overlap the BBM, but the BBM is accounted for in the line below:
/* 4 non-ECC bytes are added before each ECC bytes section */ bytes -= 4;
Normally those 4 bytes are all free OOB, but for the first ECC step, those are split into 2 free bytes and 2 BBM bytes:
/* * The first 2 bytes are used for BB markers, hence we * only have 2 bytes available in the first user data * section. */ if (!section && ecc->engine_type == NAND_ECC_ENGINE_TYPE_ON_HOST) { oobregion->offset = 2; oobregion->length = 2;
return 0; }
So if we subtract 4 bytes for the each free OOB area, including the first one, and also subtract 2 bytes for the BBM, we are double-counting the BBM. I should have made my commit message clearer. But I am going to drop this patch anyway.
Regards, Samuel
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