Re: [PATCH v2] mtd: spinand: Add support for Etron EM73D044VCx

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Bert,

bert@biot.com wrote on Tue, 14 Sep 2021 22:03:49 +0200:

> On 9/14/21 7:49 PM, Richard Weinberger wrote:
> > ----- Ursprüngliche Mail -----  
> >> bert@biot.com wrote on Wed,  8 Sep 2021 22:16:19 +0200:
> >>   
> >>> This adds a new vendor Etron, and support for a 2Gb chip.
> >>> 
> >>> The datasheet is available at
> >>> https://www.etron.com/cn/products/EM73%5B8%5DC%5BD_E_F%5DVC%20SPI%20NAND%20Flash_Promotion_Rev%201_00A.pdf
> >>> 
> >>> Signed-off-by: Bert Vermeulen <bert@biot.com>
> >>> ---
> >>> v2:
> >>> - Made ooblayout_free/_ecc depend on chip-specific parameters, instead of
> >>>   hardcoded to this 2Gb chip only
> >>> - Fixed manufacturer ordering
> >>> - Fixed minor formatting issues as reported
> >>> - Removed debug comment
> >>> 
> >>>  drivers/mtd/nand/spi/Makefile |   2 +-
> >>>  drivers/mtd/nand/spi/core.c   |   1 +
> >>>  drivers/mtd/nand/spi/etron.c  | 104 ++++++++++++++++++++++++++++++++++
> >>>  include/linux/mtd/spinand.h   |   1 +
> >>>  4 files changed, 107 insertions(+), 1 deletion(-)
> >>>  create mode 100644 drivers/mtd/nand/spi/etron.c  
> >> 
> >> [...]
> >>   
> >>> +static int etron_ecc_get_status(struct spinand_device *spinand, u8 status)
> >>> +{
> >>> +	switch (status & STATUS_ECC_MASK) {
> >>> +	case STATUS_ECC_NO_BITFLIPS:
> >>> +		return 0;
> >>> +
> >>> +	case STATUS_ECC_HAS_BITFLIPS:
> >>> +		/* Between 1-7 bitflips were corrected */
> >>> +		return 7;  
> >> 
> >> Mmmh this is a bit problematic, having no intermediate value means a
> >> single bitflip will trigger UBI to move the data around as its
> >> threshold will be reached. Richard, any feedback on this?  
> > 
> > So, the NAND controller can only report "no bitflips", "some bitflips", "maximum biflips" and "no way to fix"?
> > If so, yes, this is problematic for UBI because it will trigger wear-leveling way too often.
> > On a medium aged NAND I'd expect to see STATUS_ECC_HAS_BITFLIPS almost always set. :-(  
> 
> Yes, that's all there is according to the datasheet. Can't be _that_
> unusual, since that's all the STATUS_ECC_* flags cover.

I forgot about that part which was reminded to me by Richard:

https://elixir.bootlin.com/linux/latest/source/drivers/mtd/mtdcore.c#L627
	/* default value if not set by driver */
	if (mtd->bitflip_threshold == 0)
		mtd->bitflip_threshold = mtd->ecc_strength;

So this is fine.

Thanks,
Miquèl